# Optimum MoCA tx/rx power?



## tapokata (Apr 26, 2017)

I have a very simple two node MoCA network established between a Bolt and a non-vox (MoCA 1.1) Mini. The MoCA channel is set to automatic, which the Network troubleshooting screen reports as channel 15. The Bolt establishes the network, as television reception is OTA.

The PHY transmit link rate is 290 mbps between the Bolt and the Mini; the PHY receive link rate is 280 mbps. The transmit power is shown as -27.00 dbM, and the estimated receive power is around -49 dbM. The rx power is at the minimum expected for E band, per the MoCA specification, but my understanding is that TiVo uses the D band?

My the MoCA network is two nodes, running to a single 2:1 splitter, although the cable leads on both legs are about 50' in length. There is a POE filter installed on the input end of the splitter.

Is -27 dbm the best that I can expect for transmit power? And does -49dbM indicate this is an E band or D band usage? Any tips on how I could improve on reducing the transmit power?

I have attached a simple topographic view of my OTA MoCA network.

Thanks in advance -


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## krkaufman (Nov 25, 2003)

You're not going to get better than that. -30dBm is the maximum power reduction in the spec and I've only seen -27 dBm in actual use.

You're most definitely in great shape.

p.s. A quick test would be to hook the Mini up directly to the BOLT's coax port and check the MoCA stats. (You'd temporarily lose the TV signal during the test, of course, but it'd give you an idea of the best stats possible.)


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## tapokata (Apr 26, 2017)

Thanks for your reply!

That's a great idea on the direct hookup- I might try that one day. For the moment, I think I'll let sleeping dogs snore. I've changed the network around in a few different configurations, but want to let this settle in for a while. Maybe one day I'll test out the direct connection. It might prove interesting as a benchmark.

Thanks again-


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## tapokata (Apr 26, 2017)

I had a few minutes this morning, so I tried the direct hookup. I used a 6 inch length of RG6 coax- I can't imagine a real-world connection being any shorter- and cabled directly between the Bolt and the Mini. I also connected the Mini to another HDMI port on the TV set, so that I could look at network diagnostic results from both. 

The reported results are the same at I see from a 100' coax MoCA loop: Tx power reporting on both the Bolt and the Mini is -27.00m dBm. Interesting, the Rx power estimate is close to the spec, reporting at -29 dBm. Link rate speeds are 290 mbps Tx, and 285 mbps Rx. Looks like that's the best that can be expected between a Bolt and a MoCA 1.1 Mini.


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## tapokata (Apr 26, 2017)

Not to dig up an old thread, but found a curiosity yesterday. At the insistence of my better half, frustrated with streaming app lockups, I transposed the Bolt and Mini locations. This required adding the Tivo Bridge. The Bolt is running as a MoCA client. The Mini, for whatever reason, does not play well on ethernet- frequent V87 dropped connections, so the plan was to split the coax and keep it on MoCA, as shown:








Previously, with only one splitter in the attic between the Bolt and Mini, the transmission power was steady at -27 dbM on channel 15 (auto). In this new configuration, the transmit power increases significantly, to +3 dbM.

I wouldn't think that the splitters were directional, regarding MoCA, but when I inverted the second splitter, the transmit power decreased to -22 dbM, configured as shown below:









Anyhow, learn something new every day. The Mini is back on MoCA, and is much happier. The bride has uninterrupted Netflix/Hulu/Prime via the Bolt, so all is well.


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## tapokata (Apr 26, 2017)

So I cleaned up the coax plant yesterday- I ran a short RG6 lead from a location near my router, to the home run point in my attic. I added a Holland GHS 3-Pro unbalanced 1:3 MoCA rated splitter, replacing the 1:2 in the attic, and removing the second 1:2 splitter in the cabinet. I then moved the Tivo Bridge to the new coax lead, adjacent to the router. In doing so, I consolidated from two 1:2 splitters to a single 1:3, and essentially took the ethernet switch out of the MoCA equation. PHY rates are in excess of 275 mbps from the Mini, and 680 mbps from the Bolt (to the Bridge). Transmit power levels from both are at -27 dBm (the same power level when cabling the bolt to the mini directly over a 6" coax cable).

I am assuming somebody out here will correct me, but I used the lower db loss splitter port for the connection to the Bolt, as the Bolt is the primary OTA tuner from the antenna, and I wanted to keep the RF attenuation on that leg to a minimum.

Not too far down the road, I think I want to upgrade the Mini to a Mini Vox- not for the voice features, but for the connection speed improvements. Hoping the TiVo decides to put them on sale, at some point.

Anyhow, the attachment shows the new MoCA topography.


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## snerd (Jun 6, 2008)

Your new configuration looks clean and straightforward. Gotta love all the detail, with loss for each coax segment and connector. Best diagram I've seen posted to TCF. You're right to connect the Bolt through the -3.9dB port in order to minimize OTA signal loss.

I'm baffled by the data that you reported in post #5, because inverting the splitter that feeds the Mini *should* have done two things: 1) reduce overall loss between the Mini and the Bridge, as desired, and 2) significantly weakened the signal between the Bolt and Mini, requiring increased TX power rather than reduced TX power.

I'm guessing there may have been a problem with a bad/loose coax connector or bad splitter port that caused the problems with the Mini, since the original configuration looked a lot like your most recent diagram, except for swapping a 3-way splitter in place of two 2-way splitters.

You seem to like tweaking your setup for optimal performance, so below I'll describe a trick to get a tiny bit less loss on your OTA signals while significantly boosting the MoCA signals. Of course, "if it ain't broke, don't fix it" always applies, and your latest configuration should work quite well.

Caveat: what I'm describing below is a special configuration that only applies to a coax plant that allows the MoCA signals to be (mostly) isolated from the OTA signals. This trick is best described as a modification to the prior configuration that used two 2-way splitters.

Step 1: replace the splitter in the attic with a diplexer that has the IN/OUT port connect to the Bolt, the VHF/UHF port connected to the antenna (with or without the PoE filter, which isn't doing much in this new scenario), and the SAT port going to the Living Room. This reduces the OTA signal loss from 3.5dB through a 2-way splitter to about 1.5dB through the diplexer, and separates the OTA/MoCA signals so that no OTA signal power is sent to the Living Room.

Step 2: replace the splitter in the Living Room with this "joiner". Don't be fooled by the marketing hype that calls this a "splitter", because it behaves much differently than a true splitter. With a true splitter, RF power flows between the input port and the output ports, while the output ports are (mostly) isolated from each other. The goal of a true splitter is to distribute signals between the input port and the output ports while avoiding unwanted reflections that can interfere with reception. This joiner simply connects all three ports a single point and lets the RF signals flow in whatever way the laws of physics allow. In practice, when a device sends signals toward this joiner, about 11% of the RF power is reflected while 44% of the RF power passes to each of the other two legs. Although the reflected power in an RF system is a normally frowned upon, MoCA devices are specifically designed to compensate for the ill effects of reflections, and in fact a PoE filter intentionally introduces reflections into the coax plant to improve MoCA performance. So, in a network that has the MoCA signals isolated from the OTA signals, the MoCA signals benefit from eliminating many of the losses associated with splitters.

Some numbers: In any MoCA network, the total signal loss between a specific pair of (tx,rx) devices can vary depending on which splitters and coax segments are involved. For example, in your newest configuration, based on your numbers, the loss when data is sent from the Bolt to the Mini consists of -3.3dB coax, -3.9dB up through splitter, -0.5dB reflecting off PoE filter, -7.7dB down through splitter, -3.3dB coax to Mini, for a total loss of -18.7dB. The path between the Bolt and Bridge has a total loss of -17.7dB (1dB less loss in coax), while the loss from the Bridge to the Mini is -22.5dB.

Using the tricks listed above, the loss from antenna to Bolt is reduced by about 2.4dB (-3.9dB for splitter reduced to -1.5dB for diplexer), while the loss between the Bridge and Mini is reduced from -22.5dB to a mere -8.8dB (-2.0dB Bridge-coax, -3.5dB "joiner" insertion loss, -3.3dB coax-Mini). Bolt to Mini loss is reduced to -10.1dB.

Final Caveat: I haven't actually tried this, since I'm forced to mix MoCA and cable signals. This trick works best with only 3 MoCA devices that are isolated from any OTA or cable signals. I don't recommend using a joiner for any other purpose, especially when a true splitter is needed.


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## tapokata (Apr 26, 2017)

Hmmmmm.... interesting. I had to read this a few times, and had to take a shoe off to help with the ciphering :dizzy:, but I think I get it. 

The earlier version, with the bridge in a cabinet in the living room adjacent to the Mini, is not what I'd like to go back to- I was picking the ethernet up at that point via a switch on a fast ethernet link from my router. The latest version eliminates the switch, and keeps the "home run" point in the attic.

So, reading your fine post again... would the attached work as you intend? Note the changes in the attic section- also, any recommendation on the diplexer? Holland seems to offer two different models- the one illustrated has a slightly higher dB rejection level (40 dB vrs 35 dB).

The other minor change is the Mini- I have a Mini VOX that has MoCA 2.0 on order...

Thanks for the feedback!


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## tapokata (Apr 26, 2017)

I've attempted to work out the plant loss comparison. If the attached table is accurate, the dB gains would be:

+2.4 on the antenna leg to the Bolt
+12.4 from Mini to Bridge
+5.1 from Bolt to Mini
+5.1 from Bolt to Bridge

I know that the the TX power won't get any better than it is, currently. With a 6" cable and no splitters or other insertions, the best that the Bolt and Mini could do was -27 dBm. 

The slight improvement on the antenna leg is the equivalent of removing ~ 35' of coax from the leg.

Even if the gains are overstated, it's still substantial enough to be worth a try. I'll need to order the diplexer and joiner. 

Once more, into the attic....


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## snerd (Jun 6, 2008)

tapokata said:


> So, reading your fine post again... would the attached work as you intend? Note the changes in the attic section- also, any recommendation on the diplexer? Holland seems to offer two different models- the one illustrated has a slightly higher dB rejection level (40 dB vrs 35 dB).
> 
> The other minor change is the Mini- I have a Mini VOX that has MoCA 2.0 on order...
> 
> Thanks for the feedback!


Your diagram looks fine, assuming that you didn't intend for the shape of the diplexer to reflect port locations. Physically, the IN/OUT port is on one side while the VHF/UHF and SAT ports are on the opposite side.

The DPD2 is what I've used. It is readily available and inexpensive. I suspect any *satellite* diplexer would work, but higher rejection is probably better as long as the insertion loss is low.


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## tapokata (Apr 26, 2017)

Correct- the diplexer port locations are not as actual- my schematic skills are somewhat limited . 

Also, in looking over the Holland specs for the MoCa GHS-PRO-M 1:3 splitter, the insertion loss is a bit higher in the MoCA D band (1125-1675 Mhz)- 6.0 dB / 11.0 dB, compared to the OTA frequency range insertion loss of 3.9 dB / 7.7 dB, so the gains should be a skosh better

I've just ordered a DPD2 and the joiner. I'll log some PHY and Tx rates for all nodes, before and after, and post those results for the crowd.

Thanks for the intriguing idea, and for checking my work!


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## snerd (Jun 6, 2008)

tapokata said:


> I've attempted to work out the plant loss comparison. If the attached table is accurate, the dB gains would be:
> 
> +2.4 on the antenna leg to the Bolt
> +12.4 from Mini to Bridge
> ...


I believe the dB gains should be +7.1 for both the Bolt to Mini and Bolt to Bridge. Counting losses is different when using a diplexer rather than a splitter. With the splitter, the PoE filters is the mirror, and the MoCA signals pass through the splitter twice, first up through the splitter to reach the PoE/mirror then back down through the splitter after reflecting off the PoE/mirror. Technically, it might be more accurate to count PoE loss twice due the the reflection, but we can ignore that since the PoE losses are the least of our worries.

With the diplexer setup, the joiner is the mirror, so the PoE filter really only impacts OTA signals. Since the PoE is no longer acting as a mirror, signals only pass through the diplexer once, so the insertion loss of the diplexer only needs to be counted once. In reality, the higher frequency MoCA signals will almost certainly experience more loss than the OTA signals, when passing through the diplexer. So, after for the PoE and diplexer losses, we get back an extra 2.0dB. Also, to be completely fair, this analysis has ignored losses due to RF energy absorbed by the joiner, as well as return loss (power reflected when signals hit the ports). I'm guessing these joiner losses are insignificant, since there are no actual components (inductors, capacitors, resistors, ferrites) like there are in splitters and diplexers, and components absorb more RF power than short bare wires in the joiner.

Another little tidbit has to do with the fraction of the MoCA signal that is reflected back toward the transmitting device. When the Bolt is sending, the net signal reflected by the PoE plus splitter is -8.3dB (-3.9dB + -0.5dB + -3.9db), which means that 14.8% of the RF power going into the splitter comes back toward the Bolt. In comparison, joiner alone reflects only 11.1% of the RF power (-9.5dB), net signal reflected by the joiner plus diplexer is -12.5dB (-1.5dB + -9.5dB + -1.5dB), which is only 5.6% of the RF power going into the diplexer. So, the diplexer/joiner reduces the amount of RF signal that is wasted by being relfected back toward the Bolt. When the Bridge is sending, the splitter/PoE case has -15.9dB return (-7.7dB + -0.5dB + -7.7dB) or 2.6%, while the bare joiner returns 11.1% (-9.5dB). So, when using the diplexer/joiner, the Bolt has less returned power but the Bride has more returned power.

If you want to really build this, then you might consider a joiner like this or that to connect directly to the diplexer, eliminating the short coax. One worry with these joiners -- some reviews on Amazon say that these are poor quality and the male end may fail while merely being attached to the diplexer. Perhaps the CESS are better quality, I've never bought any of these so I don't really know from personal experience. If you do shop around, be sure the get F-type and not SMA which are smaller and won't work.


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## snerd (Jun 6, 2008)

tapokata said:


> Correct- the diplexer port locations are not as actual- my schematic skills are somewhat limited .
> 
> Also, in looking over the Holland specs for the MoCa GHS-PRO-M 1:3 splitter, the insertion loss is a bit higher in the MoCA D band (1125-1675 Mhz)- 6.0 dB / 11.0 dB, compared to the OTA frequency range insertion loss of 3.9 dB / 7.7 dB, so the gains should be a skosh better
> 
> ...


Glad to "help" but I hope you'll think of it as more of an (amusing?) experiment. I'll be very surprised if the PHY rates change significantly, since your numbers are already as good as it gets. Of course, going to a Mini Vox changes everything. It sounds like your Tx power is already minimum, so other than changes to Rx power, the only meaningful improvement might be better reception on marginal OTA channels.


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## tapokata (Apr 26, 2017)

Thanks. I've been told that the rule of thumb for a butt connector (female-to-female) is an insertion loss of 0.5dB. I considered the styles you suggest, but opted for the all female style that you first proposed- as I'm a bit obsessive about this, I torque the F connectors on splitters, taps, etc to 20 pound-inch of force, and any f-connector on an electronic device (like the Mini or Bolt) to 10 pound-inches. The short cable splice isn't going to throw things too far out of balance, and as always, I'll build and test that cable prior to installation, with an overall length of about 3". 

And while it probably wouldn't be needed, I will still keep the POE filter on the UHF\VHF port of the diplexer. Belts and suspenders, and all that.

Yeah, it's an amusing experiment, and likely just gilding a lily. Given the longish coax runs (the antenna lead comes off the roof, runs to the middle of the attic, then down a chase to a crawlspace beneath the floor, and back up to outlet location for the Bolt), saving a few dB in the plant is a worthy endeavor. That said, I may end up testing it, but revert to the splitter solution, as from a "future proof" solution, the one detriment in this configuration is OTA signals are limited to essentially one receiving location. That's not a showstopper at the moment, as I am only using the TiVo devices for OTA tuning. Down the road, there might come a day when having OTA RF available on all leads is a need.

The various bits and pieces won't start to arrive until sometime in the next week. I'll post the results when I get it pulled together. The improvements for the OTA won't likely show up as a big number change, as the RF Gain control in the Bolt basically normalizes near everything to a "72" on the signal strength scale, but I will test that as well.


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## snerd (Jun 6, 2008)

tapokata said:


> Thanks. I've been told that the rule of thumb for a butt connector (female-to-female) is an insertion loss of 0.5dB. I considered the styles you suggest, but opted for the all female style that you first proposed- as I'm a bit obsessive about this, I torque the F connectors on splitters, taps, etc to 20 pound-inch of force, and any f-connector on an electronic device (like the Mini or Bolt) to 10 pound-inches. The short cable splice isn't going to throw things too far out of balance, and as always, I'll build and test that cable prior to installation, with an overall length of about 3".


Clearly you've thought through a lot of tradeoffs. Being a bit obsessive can help avoid frustration whenever RF is in play.



> And while it probably wouldn't be needed, I will still keep the POE filter on the UHF\VHF port of the diplexer. Belts and suspenders, and all that.


Funny you should mention that. I thought about suggesting that you ditch the PoE to minimize OTA losses, but after checking the specs on your PoE I decided the 80dB isolation was probably more beneficial than the tiny improvement to the OTA signals. Kind of a shame to waste such a good PoE.



> Yeah, it's an amusing experiment, and likely just gilding a lily. Given the longish coax runs (the antenna lead comes off the roof, runs to the middle of the attic, then down a chase to a crawlspace beneath the floor, and back up to outlet location for the Bolt), saving a few dB in the plant is a worthy endeavor. That said, I may end up testing it, but revert to the splitter solution, as from a "future proof" solution, the one detriment in this configuration is OTA signals are limited to essentially one receiving location. That's not a showstopper at the moment, as I am only using the TiVo devices for OTA tuning. Down the road, there might come a day when having OTA RF available on all leads is a need.


Completely agree. Either way you go, there should be plenty of headroom for the MoCA signals, so OTA is likely the weakest link.



> The various bits and pieces won't start to arrive until sometime in the next week. I'll post the results when I get it pulled together. The improvements for the OTA won't likely show up as a big number change, as the RF Gain control in the Bolt basically normalizes near everything to a "72" on the signal strength scale, but I will test that as well.


I look forward to seeing the results. Thanks for doing the experiment!


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## tapokata (Apr 26, 2017)

It's a sickness. The diplexer and joiner won't be here until late next week, but already scheming about adding Motorola MM1000 Bonded MoCA 2.0 adapters to the plant (they run about $60 each, rather than $150/pair of actiontec bonded 2.0 adapters), thus running the Bolt and Mini VOX in Gb-ethernet client mode. Bonded MoCA 2.0 devices have a PHY (link) rates of 1.2 Gbps, and MAC rates of 1.0 Gbps, compared to a little over half of that for the MoCA 2.0 single channel used on the Bolt and Mini.

_mwah-ah-ha....._


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## krkaufman (Nov 25, 2003)

tapokata said:


> Bonded MoCA 2.0 devices have a PHY (link) rates of 1.2 Gbps, and MAC rates of 1.0 Gbps, compared to a little over half of that for the MoCA 2.0 single channel


Unless you're setting-up the bonded/extended MoCA adapters in pairs with direct coax links to establish Turbo mode, you should set expectations to something short of *800 Mbps* for an effective rate between the bonded/extended MoCA 2.0 nodes. And you'll need 3 MM1000's, replacing the TiVo Bridge, if you want the same throughput to the router from either device, as well. (Standard MoCA 2.0's effective rate is half of that, 400 Mbps.)

Unless you have other devices co-located with the BOLT or Mini VOX that you're looking to service with the bonded/extended MoCA rates, I'd think standard MoCA 2.0 would suffice for just the TiVo boxes.


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## krkaufman (Nov 25, 2003)

tapokata said:


> Given the longish coax runs (the antenna lead comes off the roof, runs to the middle of the attic, then down a chase to a crawlspace beneath the floor, and back up to outlet location for the Bolt), saving a few dB in the plant is a worthy endeavor. That said, I may end up testing it, but revert to the splitter solution, as from a "future proof" solution, the one detriment in this configuration is OTA signals are limited to essentially one receiving location.


Accepting that using a diplexer as described limits the OTA signal's distribution, you can implement the diplexer bypass around the main splitter irrespective of the joiner portion of the proposed solution. You'd be looking at Option 3 in the attached diagram, rather than Options 1 or 2.


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## tapokata (Apr 26, 2017)

Hmm. Thanks. Would the N-Way splitter add back additional insertion loss on the MoCA legs? A Holland GHS-3BPro-M lists an insertion loss of -10dB at each port for the MoCA frequency, so a leg to leg splitter jump would add -20dB in loss, correct? I believe the joiner would be -3.5dB, and the diplexer @ -1.5dB. The caveat, of course, is OTA RF on only one leg, but as currently configured the only OTA device on the plant is the Bolt.

As for MM1000 fever dream, yes, I'm aware that I'd need three devices for the configuration, replacing the TiVo ECB. I'm not likely to drop another $200 for speed improvement that's likely perceptible (the wife would surely look side-eyed in my direction), but it's the equivalent of finding ways to add horsepower to my automobile, despite having no intention of ever taking it to the track. I am curious to see the difference (if any) in PHY and TX / RX dBm rates between the splitter and diplexer/combiner option.

For OTA RF on all three down legs, I'd likely run a variation option 2, with a 1x2 N-way splitter, rather than a 3-way. The 1x2 Holland has an insertion loss for MoCA at -6.0dB, or -12.0dbB jumping two ports (such as Mini to the ECB), or -18dB from the Bolt to either the ECB or the Mini (keeping a single up split to the Antenna keeps the splitter insertion loss at -3.9dB, but RF on the other two legs would be double that. Staying with an unbalanced splitter would -7.5dB to -7.8dB in insertion loss for OTA RF on the other two legs. A balanced splitter would be -6.0 to -6.8dB per leg for all three.

The theoretical loss, including from the coax runs, using the diplexer/combiner arrangement is from -8.8dB to -12.6dB, depending on the leg. On the dual splitter option, the loss is -14dB to -25.6dB. The current 1x3 unbalanced holland splitter has a theoretical loss of -14dB to -28.3. The lowest loss in all three choices is for the run to the OTA antenna (and doesn't add back the pre-Amp increase, which covers the plant loss on the OTA leg).


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## snerd (Jun 6, 2008)

tapokata said:


> Hmm. Thanks. Would the N-Way splitter add back additional insertion loss on the MoCA legs? A Holland GHS-3BPro-M lists an insertion loss of -10dB at each port for the MoCA frequency, so a leg to leg splitter jump would add -20dB in loss, correct? I believe the joiner would be -3.5dB, and the diplexer @ -1.5dB. The caveat, of course, is OTA RF on only one leg, but as currently configured the only OTA device on the plant is the Bolt.


Yes, that's the tradeoff. The magic of the diplexer/joiner is that it avoids the high losses incurred by the splitters, but only works (cleanly) on the MoCA side of the diplexer. If you're up for doing another experiment, after trying the diplexer/joiner, you could swap the diplexer for a 2-way splitter and test the OTA reception at all of your endpoints. In such a configuration, the OTA signals at the Bolt should still be pretty clean, but reception might be spotty at the Bridge and/or Mini. The problem with the joiner is that it acts as a mirror at all frequencies, so it causes standing waves throughout the coax plant. At any given frequency, the impact of the standing waves will depend on the lengths of the coax segments and stuff like that.

Crazier still would be to forego the diplexer and use a 4-way joiner like this while keeping the PoE on the antenna leg. The reflected power increases from 11.1% to 25%, so you can view the action of the 4-way joiner as taking in RF power from any port and sending it back out equally in all four directions at 1/4 the power. (this "equal reflection" property only applies to the 4-way joiner).



> For OTA RF on all three down legs, I'd likely run a variation option 2, with a 1x2 N-way splitter, rather than a 3-way. The 1x2 Holland has an insertion loss for MoCA at -6.0dB, or -12.0dbB jumping two ports (such as Mini to the ECB), or -18dB from the Bolt to either the ECB or the Mini (keeping a single up split to the Antenna keeps the splitter insertion loss at -3.9dB, but RF on the other two legs would be double that. Staying with an unbalanced splitter would -7.5dB to -7.8dB in insertion loss for OTA RF on the other two legs. A balanced splitter would be -6.0 to -6.8dB per leg for all three.





> The theoretical loss, including from the coax runs, using the diplexer/combiner arrangement is from -8.8dB to -12.6dB, depending on the leg. On the dual splitter option, the loss is -14dB to -25.6dB. The current 1x3 unbalanced holland splitter has a theoretical loss of -14dB to -28.3. The lowest loss in all three choices is for the run to the OTA antenna (and doesn't add back the pre-Amp increase, which covers the plant loss on the OTA leg).


Something seems off with those numbers. Mathematically, an unbalanced 3-way splitter is just two 2-way splitters combined in a single package, so the numbers should come out almost identical. Assuming you already have a 3-way splitter, there would be no benefit to converting to a dual-splitter configuration, since the extra coax and ports just add more potential failure points.

You might want to use a balanced 3-way splitter (e.g. Holland GHS-3BPRO-M) to improve the worst case MoCA loss by about 2dB, and get a more even distribution of OTA signal.


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## krkaufman (Nov 25, 2003)

tapokata said:


> For OTA RF on all three down legs, I'd likely run a variation option 2, with a 1x2 N-way splitter, rather than a 3-way. The 1x2 Holland has an insertion loss for MoCA at -6.0dB, or -12.0dbB jumping two ports (such as Mini to the ECB), or -18dB from the Bolt to either the ECB or the Mini ...


The above numbers seem to be assuming the nodes hanging from the secondary 2-way splittter would talk to each other directly ... "jumping two ports" ... which would require using the splitter's output port isolation loss figure to determine the loss budget between the nodes. This path's total loss could be compared to the loss associated with the path that reflects off the "PoE" MoCA filter (not forgetting the filter's insertion loss), and the path with the lesser loss would be what the MoCA gear should settle upon.

The following slide illustrates the "PoE" MoCA filter difference, though you probably really want to review the whole presentation (Doug MacLeod's 'MoCA Basics' presentation) ... or at least pages 13-22 dealing with loss budget calculation.






​


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## tapokata (Apr 26, 2017)

Thanks... I think a light bulb went on here- the isolation factor isn't included. So I've attached two documents- the first (_db loss coax plant_)is my simple math on the insertion loss for the various options, as compared to the currently installed unbalanced splitter. I had done this without consideration to the isolation numbers. The only splitter port that uses the RF frequency loss is the leg running to the antenna (the Bolt is the only RF tuner connected in the plant), and that number reflects loss from 600-1000MHz, as until the 2020 FCC "re-pack" there are still a couple of local OTA stations broadcasting above 600MHz. All of the other splitter insertion loss numbers are for the MoCA frequencies.

The balanced 3-way has a higher loss for the OTA RF leg, then passing through one of the 1x2 balanced splitters... and my goal for considering the diplexer/joiner option is to reduce the insertion loss.

The second (_insertion loss specs)_ is a summary of the specs, cribbed from the Holland catalog. (Edited, as I just noticed the last paragraph with the MoCA doc). I'll review and revise the budget... It should go without saying, but I appreciate the education from you folks (I'm a retired printer, not an Electrical Engineer)- it's been informative. You guys are great, and I've learned a great deal here. I do appreciate your consideration, and I apologize if I've been annoying...


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## tapokata (Apr 26, 2017)

Ok, I'm reviewing all of this- and thank you. A (edited) questions:

1.) (edited) Nevermind my first question. It was about installing an additional POE filter, but I realized it would block frequency traffic where it shouldn't be restricted...

2.) Should I at all be concerned about "Return Loss" in the budget loss plan for the OTA antenna feed? The Holland specs list both an input and output return loss of 20dB up to 1000 MHz; there's no loss spec at the MoCA frequency levels.

Thanks!


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## snerd (Jun 6, 2008)

tapokata said:


> 2.) Should I at all be concerned about "Return Loss" in the budget loss plan for the OTA antenna feed? The Holland specs list both an input and output return loss of 20dB up to 1000 MHz; there's no loss spec at the MoCA frequency levels.


Return Loss is the fraction of RF power that is reflected back from whatever port is accepting the power, so it represents RF power that is returning to the source, and it is counted as a loss since that power can't reach the intended receiver. More dB is *usually* better, but MoCA systems with a PoE filter will have overall return loss that is a comparitively high percentage (low dB) because of the mirror effect of the PoE filter (or joiner). 20dB means that 1% of the RF power is reflected back, and 30dB means that 0.1% of the RF power is reflected back.

Holland probably doesn't spec return loss for MoCA frequencies because the reflected power from the PoE filter usually swamps out the power reflected by the splitter, so it isn't relevant.


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## tapokata (Apr 26, 2017)

How would I account for the return loss in an OTA loss budget? If the return loss is 20dB, am I adding that in with the other insertion loss and cable loss? Sorry to be so thick-headed.. thanks.


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## snerd (Jun 6, 2008)

krkaufman said:


> The above numbers seem to be assuming the nodes hanging from the secondary 2-way splittter would talk to each other directly ... "jumping two ports" ... which would require using the splitter's output port isolation loss figure to determine the loss budget between the nodes. This path's total loss could be compared to the loss associated with the path that reflects off the "PoE" MoCA filter (not forgetting the filter's insertion loss), and the path with the lesser loss would be what the MoCA gear should settle upon.


RF Nitpick: MoCA gear doesn't actually choose between two different signals. At any single frequency, the signal due to the port isolation will combine with the signal that passes through the splitters and reflects off the PoE filter. A MoCA receiver can only see the combined signal, and the relative phase of those two portions will determine whether they add constructively or destructively. The net loss will have a magnitude in dB than ranges anywhere from the sum of the two dB values to the difference between the two dB values, depending on the relative phases. If the two parts are nearly equal in magnitude with a phase difference that results in destructive interference, reception may fail because the combined signal will is too weak to detect. In such a case, the MoCA system will adapt to prefer frequencies with constructive interference while avoiding frequencies with destructive interference.

Soapbox: In my opinion, Holland's (and other) "MoCA splitters" are more of a marketing gimmick than an actual benefit, and my discussion of constructive/destructive interference above explains why they might do more harm than good. WIth a proper setup that uses a PoE filter at the top of the splitter tree, it would be better to have infinite port isolation so that the MoCA receiver always has a clean signal that is free of constructive/destructive interference from multiple signal paths. That simplifies the proper calculation of path loss and avoids the possibility that destructive interference will reduce the signal rather than improve it.


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## snerd (Jun 6, 2008)

tapokata said:


> How would I account for the return loss in an OTA loss budget? If the return loss is 20dB, am I adding that in with the other insertion loss and cable loss? Sorry to be so thick-headed.. thanks.


Quick answer: just ignore it.

Long answer: a 20dB return loss is equivalent to 99% of the power making it into the port, so if you want to think in terms of "port insertion loss" then the number would be -0.044 = 10*log10(0.99). However, you don't actually need to make an adjustment, because the insertion loss numbers already account for the fact that some of the RF power doesn't make it through the splitter, and the energy absorbed inside the splitter is generally much larger than the tiny bit that bounces off the port without getting in.


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## snerd (Jun 6, 2008)

tapokata said:


> Thanks... I think a light bulb went on here- the isolation factor isn't included.


Yeah, the real problem accounting for that involves constructive/destructive interference as discussed above, and the reality is that you can't really combine them because the MoCA adapters will tend to ignore frequencies that just happen to destructively interfere and select frequencies that just happen to constructively interfere, and you have no meaningful control over those frequencies.



> So I've attached two documents- the first (_db loss coax plant_)is my simple math on the insertion loss for the various options, as compared to the currently installed unbalanced splitter. I had done this without consideration to the isolation numbers.


The "Mini to Bridge" column of the "tiered splitter plan" ignores the #1 splitter and the PoE filter, as if the signals were being reflected at the input port of #2 splitter. In reality, the signal from the Bridge to the Mini will go up through the #2 splitter, then up through the #1 splitter, reflect off the PoE filter, then down through both splitters to reach the Mini. The net result will be -1dB compared to the 1x3u splitter. The 1x3u splitter might actually be a tiny be better than using two 2-way splitters, since the extra coax and connectors and such have a small impact, but the 1dB difference might be mostly due to roundoff error from the spec sheets. The internals of the 1x3u splitter really do look just like two tiered 2-way splitters.


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## tapokata (Apr 26, 2017)

Got it, thanks. I'm convinced that the tiered splitter plan isn't worth looking at. It looks like I'll have four different test scenarios to run:

a.) "baseline"- that will be a straight coax cable (less than 1') from the TiVo ECB to the new Mini VOX. That keeps the Bridge in play, as it will be in the plant. I will record Tx Power, Est Rx power, Tx PHY and Est Rx PHY rates

b.) current unbalanced splitter configuration, with above data points reported from the Bolt to the Mini Vox, Bolt to Bridge, and Mini VOX to Bridge

c.) diplexer/joiner configuration, with same data points.

d.) Krkaufman's 3x1 splitter and diplexer configuation, using the unbalanced splitter.

I'll also check OTA signal strength at the Bolt, such as it is, under all three OTA scenarios, recording the initial strength readout, final strength readout after two minutes, and peak readout as reported by the Bolt. These numbers are somewhat dubious, in that the automatic gain control in the Bolt basically adjusts everything to "72" on the scale (you'd think the TiVo engineers would have a sense of humor, and had a "Spinal-Tap" like scale that adjusts everything to "11"). 

I'll test OTA strength on three different RF channels- a Hi-VHF station at 186MHz minimum (Channel 9, actual), a UHF station (Channel 35, actual) at 602 MHz maximum (the max frequency allowed after the FCC "re-pack" in 2020) and the current UHF station max at 680Mhz (Channel 48, actual).

That ought to keep me busy. The Mini VOX won't arrive for a couple of days, and the joiner a few days after that, and the diplexer either by the end of this week, or early next.

Thanks to all for my continuing education. It's been informative.


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## tapokata (Apr 26, 2017)

The test results are in (*TL/DR version*: _Three plant configuration options: (a) splitter (b) diplexer and splitter, (c) diplexer and combiner. Diplexer use appears to improve local signal strength as reported- results taken with a shaker of salt. MoCA power rates are unchanged. PHY link rates are slightly degraded by use of combiner, although likely not significant. OP has chosen to remain with configuration (b): diplexer and unbalanced 3-way splitter._)

The premise: Will a change in a relatively straightforward coax plant, (a) improve MoCA PHY rates and lower transmission power and/or (b) improve OTA signal reception at the TiVo Bolt.

Plant Configuration: Three coax drops connected to a home run location in the attic: (1) Mini Vox, (2) TiVo Bridge, and (3) TiVo Bolt in OTA mode. The down-lead to the home run location is from a roof top mounted antenna and preamplifier, providing in-band OTA services to the Bolt. The Bolt is acting as primary tuner box for the entire household, distributing service to a Mini Vox. Bolt has no ethernet available at the immediate location, only MoCA; Mini Vox has fast ethernet & MoCA; Bridge provides MoCa services to plant from a location adjacent to network router.

The original configuration utilized a 3-way unbalanced splitter in the attic:










The next option was to add a diplexer and additional PoE filter, isolating the Bridge and Mini Vox from in-band frequencies. This is the model suggested by krkaufman:










The last option was suggested by snerd, which replaced the unbalanced splitter with a 3-way 75 OHM combiner. This configuration is NOT recommended for down leads with in-band OTA frequencies.










A brief note on the OTA configuration. The antenna is located ~ 20 miles from the primary broadcast towers supporting the metropolitan area. The Noise Margins, as reported by TV Fool, are relatively strong, and the use of the pre-amp is intended to make up for the insertion loss associated with long cable runs (the coax lead from the roof, which runs through the attic, down an interior chase to the crawlspace, and back up to the jack location can be as much as 120').

The TV Fool report NM does not take into consideration any local vegetation impediments, but the LOS signal path from my antenna takes this through the canopy of a 70+ year old London Plane Sycamore (think big lobed leaves, maple like in shape, but about the size of your palm). The canopy spreads over 40 feet, and the nearest edge is about 40 feet from the antenna. Needless to say that the signal is pristine in the winter, but during the other three seasons, the application of any wind creates significant multi-path problems. From anecdotal viewing experience, this interference occurs only on two frequencies... both of which will change in two years when the FCC repack is completed... so you see, I have hopes. The tree is a heritage tree (can't be removed or altered without city planning commission approval) in a neighbor's yard, and is far to tall for me to get an LOS position short of erecting a huge free standing tower, or adding on a multi-story addition to the house.

TVfool report and Google maps photo cropped from AntennaWeb page, are as follows. The transmitter band for the primary stations (in yellow) passes through the tree to the bottom of the photo:









It's also worth noting that the use of a pre-amplifier with strong broadcast signals can result in overload of the tuner- not enough to cause damage, but can cause some interference, drop outs, or signal blinds. I found some planning docs on-line that allow you to plug in antenna gains, ERP ratings, distance, channel frequency, etc- the yields the estimated signal power (dBm) at the tuner input; the results are that -10 dBm is the maximum power presented, and -15 dBm or lower as optimum levels. These planning docs are included in the master workbook that I can forward by request, but reducing the insertion loss on the in-band lead did not create an overload situation.

The channel data is summarized in the following table:










I collected all of the relevant data I could find regarding insertion losses for devices in the coax plant. The fixed losses, described by drop and down-lead, don't include the variable equipment for the test. The IL numbers are calculated, and do not include any loss or noise factor from the pre-amp, nor the (unreported) noise/loss from the TiVo Bolt.









These fixed losses were then inserted into another document that calculates the total loss, based on the option:








As shown, the use of the reduces the insertion loss on the in-band leg (Antenna to Bolt) by about 2.8 dB. The use of the signal combiner reduces the insertion loss on the MoCA legs by 11 to 17 dB. With those differences, I felt it was worthwhile to proceed with the test.

So the test methodology was simply to observe and record the PHY and power rates shown on the network settings pages of the Bolt and the Mini Vox, with an "overnight" interval before recording the results, and 24-hour in-service period for each configuation.

The in-band signal strength test, such as it is, was performed by putting the bolt into antenna signal strength test mode, then keying in the test frequency. I observed the initial strength graph number, then recorded that same number after 2 minutes, as well as the peak. The two in-band tests were done in mid-morning (about 10 AM local time), when the winds were calm. The antenna bearing to the tower was consistent with the Tvfool report.

The recorded results are in the following tables:

(a) In-band reported signal strength numbers:









(b) MoCA PHY rates and Power numbers:









The "baseline" testing was done using a 3' length of RG6 coax, connecting the Mini Vox and the Bridge- in an attempt to provide a ceiling value for any expected changes. The Est Rx Power number is not what was expected- in fact, I changed out the cable (using a manufactured cable the first time, and a home built cable the second) with no change in result. I could speculate that the estimates are unduly influenced by reflections form the close proximity of the devices, but I really don't know.

The PHY and Power rate differences for the three options are not large enough to be material, although the use of the combiner yielded slightly lower PHY rates, although again not enough to affect viewing performance.

The diplexer use did improve reported signal strength, but there are a zillion caveats to this test, chief among those is the use of an Automatic Gain Control by the Bolt, which brings most strong-ish signals to a "72" maximum- about "30" off from the Hitchiker's Guide to The Galaxy constant.

Your mileage, of course, will vary considerably, as the loss calculations are specific to this location.

As for now, I'm going to stay with "option B", running the diplexer and unbalanced splitter configuration.

Sorry for the long diversion.


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