Originally Posted by Larry Kenney
A neighbor asked me about getting an antenna for OTA. He's got a Dish Network 722 and wants to record using the OTA input. The problem is, he wants to be able to record stations that are 3/4 mile away to the west on Sutro Tower, 5 miles away to the south on Mt. San Bruno, 35 miles away to the southeast in the South Bay and a station that's 45 miles to the north and not have to worry about where the antenna is pointing.
I didn't have a good answer. I told him that with a fixed antenna pointed to the south he would get most of the stations, but probably not all of them. The ones 3/4 mile away would be strong enough to come in off the side and the ones 5 miles away to the south would be good and strong, but the stations 35 and 45 miles away would maybe come in, maybe not.
I set my 10-7-13 - 4228 combo pointed south and we took a look at what we actually received. What I told him was pretty close to being right. All Sutro and Mt. San Bruno stations were solid, although one of the Sutro stations was only at 70%. Three out of the five from the southeast were pretty strong. The other two and the station to the north that's 45 miles out were "No Signal".
I was wondering... do any of you know if there is an omni-directional antenna that will receive stations up to 45 miles away that could be used for instances like this? Multipath, I guess, could be a big problem with such an antenna but is there one that's available to try?
Thanks for your input.
I entered your neighbors approx. location into TVFool...it's near corner
of Douglas St and 19th St in Eureka Valley, CA (give or take a few tenths):http://www.tvfool.com/modeling/tmp/0.../Radar-All.png
At that location, signals to North just miss nearby Buena Vista Peak
and pass over the Presidio high lands. The signal SE passes right over
the hills on Hunter's Point. Otherwise, local terrain isn't a problem.With an OMNI antenna,
extremely high signals from Sutro Towers
will generate Adjacent/Next Adjacent/Next-Next Adjacent/Etc
Interference plus Intermod Products, so you shouldn't expect
to receive signals anywhere close to "normal" sensitivity levels,
so fergit about anything below about NM=10-15 (give or take).
And you should use a Variable RF Attenuator to reduce signal
levels so you can optimize the remaining dynamic range.
[Inserting 10 dB of attenuation, reduces Intermods by 30 dB.]
Unfortunately, input attenuation doesn't help the Adjacent (etc)
Channel problem. In order to receive a weaker adjacent channel,
strong channels need to be no more than 33 dB
than the desired, which is violated by Ch7/8 and Ch34/35, etc.
[In TVFool, Adjacent Channel problems are tagged with an "a".]
Next Adjacent (N+/- 2), Next-Next Adjacent (N+/- 3), etc, etc
need to have no more than 40-50 dB
These are per CECB Converter Box Specs (mandatory) and
ATSC A/74 Receiver Guidelines, non-mandatory, so YMMV....
[These are NOT tagged in TVFool.]
So Ch7 probably prevents reception of Ch9/10 (KVIE/KXTV from 55/57-deg).
And Ch29 probably prevents reception of Ch27 (KTSF from 177-deg).
And Ch38 probably prevents reception of Ch36 (KICU from 120-deg).
And Ch39 probably prevents reception of Ch41 (KKPX from 177-deg).
And Ch45 probably prevents reception of Ch49/50/51 (From 120-deg).
That eliminates all of the stations at about 62-mi range NE towards 56/57-deg
(not 45-mi)....which you don't need anyway since they're all duplicates.
Four stations at about 36-mi range SE towards 120/120-deg are in the
iffy reception zone wrt signal levels and Adjacent/Next Adjacent Channel
Interference probably blocks reception. Ch14 and Ch34 are Spanish
language stations that might not be of interest to your neighbor.
He also may or may not be interested in KICU (Ch36) and KQEH
(PBS Ch50, aka KQED-Plus).
That only leaves nearby Sutro Towers, K14MW-D (Ch3 from 325-deg)
which is fairly strong and three stations from San Bruno Towers (177-deg).
Note that in addition to Lo-VHF Ch3, there are three Hi-VHF stations:
extremely strong Ch7 from Sutro Towers and Ch8/12 from San Bruno Towers.So an OMNI antenna should get the two local Towers plus probably Ch3.
You should NOT use any amplifiers.....except possibly a low Gain Distro Amp,
IF NECESSARY...which is preceded by that Variable RF Attenuator.
A multiple antenna system might be able to add some of the above
"blocked" channels...but it would help to know which ones are a priority.