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Old 3-Nov-2014, 7:01 PM   #31
Antennas Direct Tech Supp
Join Date: Jan 2010
Posts: 2,932
A few observations about the most recent discussions.

Tivo's statement of the required SNR, as rabbit73 already noted, is bogus. They were quoting QAM information, not ATSC. A perfectly tuned ATSC transmission plant rarely does better than 35 dB or so. However, since the Roamio does have four tuners, it would be safe to assume that they have integrated an input amplifier followed by a four port splitter into the front end of the tuner so as to best avoid splitter loss while doing their best to maintain a low input noise figure and a reasonable input signal power capacity.

I was surprised to see improvements in signal strength and the RS Uncorrected numbers across the board
I'm not. That's why I suggested the configurations previously, to get rid of system configuration errors that were degrading the SNR.

Is there any risk damaging a TV tuner sending that much signal to a single tuner?
Nope. Tuners are equipped to handle a lot more than your system can possible feed to it.

Upon receiving your coordinates, they resolve to the northeast corner of your roof where aerial photos show a satellite dish installed. I've surmised that you're using that existing mount for the 91XG.

Based on your coordinates, you're about 200' below the rim of a steep hillside across the creek valley. The signal path to KRBK crosses the highest elevation near the intersection of N 3rd and E. Indian Valley Dr. then drops towards you, then finally into the valley. It has been my experience and observation that the closer one is to the terrain obstacle causing the diffraction of the signal, the more inaccurate is the guesstimate of received signal strength from the TVFool simulation engine. I suspect that the signal forecasts for KRBK's signal is probably too optimistic.

In all, the one change I'd recommend making will be exceptionally difficult and that's getting the 91XG up to the peak of the roof of the second story instead of down low on the old satellite mount at the back of the garage. That would likely get you an additional 20+' of elevation and I'd expect it to help tremendously with your reception of KRBK. I'd also expect a serious level of difficulty getting it up there.

Today, 10-1 fluctuated off the 0 RS Uncorrected to around 60 which caused some of those picture issues I described early in this thread.
It is VHF being received by a simple not-very-directional dipole. Most likely due to impulse or electrical noise from nearby.

33.1 KSPR real channel 19 is your strongest signal. It could be getting close to an overload point somewhere in your system.
I think he's fine as long as he doesn't amplify the C2V's output. If we accept the simulator's estimate of about -25 dBm at the antenna, add in 8 dB for antenna gain, subtract 1-2 dB for the insertion loss of both the AC7 and integrated U/V combiner, subtract 3 dB of coax loss (about 50'), and subtract the Roamio's tuner noise figure (??), we're still well under -20 dBm signal power at the inputs to the individual tuners which would be expected to tolerate maximum signals up to nearly 0 dBm.
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Last edited by ADTech; 3-Nov-2014 at 8:29 PM.
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