Well, just didn't get around to it yesterday. I'd actually almost suggest the PA18 for its better noise performance but the calculated signal power of KMOS would cause a violation of a rule I made for our sales staff: If there's any "green" on the plot, do not use the PA18. That would either eliminate it completely or, at least, for the north-pointing 91XG unless KMOS was notched out. By that time, things are quickly getting out of control in terms of complexity plus I didn't look at post 2020 channel assignments. FWIW, the power supply and inserter shipped with the Juice is more than capable to supply two of them simultaneously. The amp usually pulls 120-140 mA at 12 volts and the supply is rated at 400 mA output.

I don't think so. He pointed out a factor I hadn't considered. I happen to ALWAYS view these installations as experiments with no expectation as to the outcome. Sometimes they work out okay, sometimes they fail miserably. Usually, they work so-so with some wierd issues due to the problems inherent with combining signals in an uncontrolled manner.

Thank you for the clarification.
A good way to view them.
I couldn't get my head wrapped around what he said:
Is he talking about "noise" that is from the internal NF of each preamp, or he is talking about other "noise" that is added to the NFs of the preamps from the mis-aimed antenna?

I am inclined to believe Tower Guy because he has extensive RF experience and knowledge, but I would have to demonstrate it to myself to see what would happen and I don't think I have the necessary equipment.

If one antenna and preamp was receiving channel A with an SNR of 18 dB, and the second antenna (aimed in a different direction) and preamp was receiving channel B also with an SNR of 18 dB, would the SNRs of both signals then be 15 dB after combining because of the NFs adding together, or would the result be difficult to predict because of the contribution of other "noise" from the antenna not properly aimed at the desired channel?

That paragraph is exactly correct.

Thank you for the clarification.

I think I understand how the notch filter (or attenuator) on the output of the antenna not aimed at the desired channel will help, but is there any other way of combining that would retain the SNRs of the antennas not combined for the OP other than single channel amps as in a headend?

Is combining after the power inserters using two coax lines, equivalent to combining after the preamps using just one coax line as far as results are concerned?

Combining the Ouput of Two Preamps can Reduce Weak Signal Sensitivity
 

I assembled what equipment I had on hand to investigate what happens when the output of two preamps are combined with a splitter in reverse.

Equipment used:

Blonder Tongue HAVM-1UA Agile Modulator - 470-806 MHz, output ~ +30dBmV
Sadelco DisplayMax 800 Signal Level Meter (SLM)
Sadelco 719E Signal Level Meter (SLM)
2 Channel Master 7777HD Preamps
RCA TVPRAMP1R Preamp to increase sensitivity of SLMs
2-way splitter used as a combiner
3 20dB fixed attenuators
1 10dB fixed attenuator
1 6 dB fixed attenuator

For a test signal, I used the video carrier of analog channel 20 from the modulator.

The 6 dB attenuator was used to adjust the sensitivity of the SLM to keep the readings centered on one range of the SLM to avoid switching to another range. The noise floor of the measurement system was well below the noise from the 7777HD, so the NF of the RCA preamp could be ignored.

http://forum.tvfool.com/attachment.p...1&d=1440873529

I made the first measurements with the DisplayMax 800 SLM, on the right in the photo. The modulator signal is quite stable within 0.1 dB, and the SLM has 0.1 dB resolution. However, I had a problem measuring the random noise from the CM7777HD because the SLM digital display would follow the rapid changes, making it difficult to read. I switched to the 719E SLM (on the left) and its slower response was able to average the noise reading for me. The noise was measured on a nearby channel not used by the modulator.

http://forum.tvfool.com/attachment.p...1&d=1502665287

http://forum.tvfool.com/attachment.p...7&d=1498343132

I then added a combiner and the second CM7777HD. I do have two modulators, but not enough attenuators to feed a weak signal to the second 7777HD. This shows the affect of the noise from the second CM7777HD on the SNR of the CH 20 signal:

CONCLUSION:

My equipment isn't lab grade, but I have enough confidence in my measurements to conclude that combining the output of two preamps with a splitter in reverse causes a loss of sensitivity that can have a critical negative affect on marginal signals near the digital cliff.

Hello,

I wanted to show off a bit. I completed erecting my tower. I am receiving all channels I expected. What surprised me is I didn't need a preamp to get all those channels. 35 miles is the closest tower and 70 miles is the farthest. I appreciate everyone's help along the way. I'm thinking about what else I can play with. Maybe something with FM or FTA.

https://forum.tvfool.com/attachment....7&d=1553180949

https://forum.tvfool.com/attachment....1&d=1553180974

What a great looking setup! How high is your tower? Is that a project box or a rotor I see up there?

Thanks! It's a 50' Rohn 25G with a 10' mast. The box is a demarcation box for coax connections. It made weather proofing the connections easier. It's big enough to house a preamp if I need to when the trees leave. I had to play with different length coax cable connections to deal with multipath interference.

Wow that's too much on that tower and is the tower grounded
and when you use a Gray box's that size I can believe the insert loss
And you should have the uhf on top and the seller's below.
Multipath.is becuse of the box??stand back and tack a good look
at where it sits and when you put your VHF in the same box.
Is not good that is why you keep the vh F out of reach.frum the uhf.
And that is why you are getting multipath and if you are looking for true vh F
you should use a separate feed line for vhf.AND use an A/B switcher frum VHF/UHF!!!
and the uhf antenna Direct 91x are too far apart that should be 3ft apart and the feed line frum the ANTENNA to the T connections should be 3ft long,and the ANTENNA Direct 91x
Should be faced the same way and the same for the seller's LAB antennas too that can all so creat MULTIPATH as well It looks like you have a good mess too fix well I had the same set up but the other way around and with the title sistom for the 91xg!!!and no MULTPATH
Prblem'S and the hi vh F 1500miles of RECEIVE range with a channel master 7777amp
And for CABLE I used RG8u frum the ANTENNA to the amp's board and close to the ANTENNA as possible for best results!!!and a good rotor too tern all 4.ANTENNAS
And the uhf RECEIVE range with a 45+45dbg,Johansson anp kit 200miles of RECEIVE range SIGNAL strength of 100%on A 150ft tower and no dropouts with my inverted V antenna for the HAM band use and my spectrometer for all my needs.

I consulted directly with Rohn before constructing. The weight and windload are well within specifications. The tower is guyed and grounded to specifications.

What does the size of the demarcation box have to do with insertion loss?

The VHF Channels are much weaker than the UHF Channels in my area. Also, the spacing needed for VHF antennas is higher than UHF. After much trial and error, this is the configuration that fit my needs.

The box is plastic and the coax is shielded. I am not ganging the antennas to boost signal. I am receiving VHF and UHF from two separate directions.

My DVR has 4 separate tuners. I realize an A/B switch would result in the best signal, but that is not the best solution for my needs.

I am not ganging the antennas to boost signal. I am ganging to achieve one input to my distribution amp.

I used solid copper core RG6 and I do not have a preamp. I do not see the need to use more expensive cable when, in my case, it is not necessary. How do you connect RG8 50 ohm wire to your TV?

Ok so know what about a uhf at 45dbg/vhf35dbg.Johansson anp kit WHERE you
Do not need a combinder? Or a T connections to add a vhf/uhf ANTENNAS

I know about the Johansson Amp Kit but the splitter rabbit73 and ADTech recommended for combining works just fine in my case. No reason to spend the money on an amp kit. In the case of OTA TV, I am looking for a signal that is "good enough" meaning strong enough not to drop out while viewing/recording. I do not need the signals to be at 100%. That may change once the leaves start coming out on the trees. I am above the trees, but since I'm 2edge on all signals but one, this has affected me in the past with prior setups. I will know in less than a month if this will be the case with the new setup.

Thanks Joe!

It could be Nice change a few things
And yes look'S that'S a lot of money involved
And the best ANTENNA and a NICE TOWER!!
And what A shame on the RECEIVE range
But with a few changes and a good tweak!!
And defentle no dropouts and all channels
Day or night and then you will have
One He'll of an ANTENNA set-up!!!!
Let's tweak it and have no dropouts single!!!!
Just like ten Hours of work.

That is why you have MULTIPATH!!
HI Gain antenna when stacking them
Have to be TRUE in line with one another
not off set,same with the ANTENNA Direct 91st
an OTHER HIGH gaIN antenna when stacking them they have to stay true
Not off set it makes MultiPATH, maybe you can adjust your antenna 'S
And to tune the ANTENNA 's but you have to get rid of the DISTRIBUTION AMP.
Hi GaIN antenna do not like them they all so creating MULTIPATH.
And they say not to use them on hi gain ANTENNA like the 91xg&seller's lab!
HI Gain!!! And why you should use a good amp I know you do not want too spend more money!! But when stacking ANTENNAs the amp is used to tune the ANTENNA's iT's
Just not about the dbg,it all so tunes. The antenna.

I do not know if you're obtuse or trolling, but I will attempt to explain to you what I believe everyone else who has read this thread has understood.

I went in to this to achieve the goal of getting all channels available in my area to combine in to one input on my DVR (TiVo). I understand why I have multipath and the inherent problems with this setup. While not ideal, this set up is performing flawlessly with no dropouts and all available channels. There are NO amount of tweaks or changes that would make ANY noticeable difference to the end user to enhance the experience. 100% signal vs. 85% signal does not matter in this case. I do not know how else to put it. As ADTech said, every antenna installation is an experiment.

I had a blast over the last 3 years getting to this point and have learned some things on the way. I did all the work myself with the help of my 8 year old son. Nothing you suggest will make anything about this experience better. I am done responding to you now. Have a nice day.

No tweaks are needed, Ken; it's an excellent installation just the way it is.

Let the man have his joy; he earned it.

rabbit