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Old 21-Dec-2011, 5:25 AM   #4
ghz24
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Join Date: May 2011
Location: Central Illinois U.S.
Posts: 72
Some where I heard a NM of 15 as minimum for low vhf (but I can't find the reference)

Quote:
Rarely does a preamp help low band VHF reception.
I thought that 15 NM had to do partly from the estimated noise floor of the tuner. IIRC that was 7 or 8 dB for low vhf and 5-6 for uhf for an "average" tuner.
So (even if it's hooked directly to the tuner) how does having a noise floor of 1 or 2 for a low noise amp not better than the stock tuners sensitivity?
And (since I would mast mount not hook directly to the tuner) how is it not an improvement to have the noise sensitive components 15-40+ feet and a house wall/roof away from the noisy interior of the house?
Are these benefits drowned out by some other factor?
I know a lot of consumer antennas have high SWR on low VHF frequency
and even SWR of 2 can raise the "effective" noise floor by 3+ dB.
(for digital signals only) due to vector magnitude error.
And amplified garbage is garbage but there is evidence that a high quality (pre) amp can help stabilize SWR and counter this effect at least some.
On my channel 4 lcd monitor, fans(ac) and microwave oven interfere with reception that I've seen for sure.
My primary plan to get channel 4 includes a "custom cut" short boomed yagi (modeled at 10 dBi ) and mounting an old digital converter box (tuned only to 4 and with the output switch set to channel 4 ) in a grounded metal box on the tower to avoid noise and overcome some cable loss.
Then joinntenna or a/b switch the analog 4
My current antenna is about 6 dBi (by rough modeling)
plan A should improve signal by ~6dB
I was thinking I wouldn't need an amp (other than the one in the tuner)
My NM is 15-16
I hope these measures will prove adequate as this borders on heroic
plan b is truly heroic and would be best avoided.
I used some calculation to arrive at needing 10 dBi.
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