OTA Geniuses... Help Me out with upgraded preamp

[Cokeswigga]

Here is my current Setup:

Winegard HD-9095 with AP-4700 Preamp.

I live in southwest riverside, and I have my antenna aimed at Los Angeles' Mt. Wilson Antenna farm. It's about a 70 mile journey as the bird flys from my antenna to the transmission antennas

I am able to tune in all L.A. Channels.

Primarily these are the stations of interest
Channel***********UHF**** Strength with AP4700****Strength with 4800
002-1 (CBS Digital)***60***********96********************94
004-1 (NBC Digital)***36***********79********************73
007-1 (ABC Digital)***53***********77********************56
011-1 (Fox Digital)****65**********78********************74

I just bought an AP4800 (higher gain pre-amp)
I was hoping that with the 4800, I would get better signal strength on all the channels.

Instead I saw the opposite. I lost a few points. No big deal, I attributed it to the increased noise of the pre-amp or something.

But what really caught my eye what I totally lost channel 53 (kabc-DT 007-1)

Now, here's a little history.
I used to have a Dish Network 811.
With the 811 I had all kinds of problems tuning in ABC.
What I found was that I turned my antenna 90 degrees to the west and point it at a nearby mountain, I could get kabc, but at a low signal (~60). So I attributed the inability to tune in KABC to multipath from the mountain. BUT it only affected this one channel!!! None of the other channels had any problem of signal issues.

So I turned my antenna back to pointing straigh at mt wilson, and just accepeted that I would have to move or blow up the mountain, or wait until a better ota receiver came out.

Low an behold, a little patience paid off. (and since blowing up a mountain would probably piss off a bunch of people), I upgraded to the Dish Network 622... which has a much better OTA receiver. All of a sudden I was able to tune KABC without any trouble.

Now today..... my questions are:

1.) Why did I not see much of change at all on all the channels with a higher gain pre-amp?

2.) Why does the higher gain pre-amp significantly effect the one channel (possible multipath)?

3.) Why does only the one channel have this problem with multipath??


Or am I totally off my assumptions..


Any help would be greatly appreciated.

Thanks

 

[Tower Guy]

Now today..... my questions are:

1.) Why did I not see much of change at all on all the channels with a higher gain pre-amp?

2.) Why does the higher gain pre-amp significantly effect the one channel (possible multipath)?

3.) Why does only the one channel have this problem with multipath??

Thanks

1.) You didn't see much of a gain with a higher gain preamp because the noise of the system did not go down. You already had enough gain with the AP-4700 to overcome the loss of the lead-in and override the noise in your receiver. The signal strength meter on a HDTV set is really a measurement of relative bit error rate, not absolute signal strength.

2.) A higher gain preamp is more likely to overload than a preamp with less gain. It's likely that your moving the antenna caused another unknown signal to drop in signal strength, hence reducing the overload caused by that signal.

3.) I doubt that it was multipath to start with. See #2. The fact that KABC-DT got much worse with a higher gain preamp is a strong indication that your preamps are overloaded.

I like your choice of the AP-4700. My AP-4700 worked better than the highly rated HDP-269 until I put a UHF only filter before the HDP-269.

The likely candidate for the unknown signal is KVCR; analog 24, digital 26.

 

[Cokeswigga]

Towerguy... thanks for the feedback!

2.) A higher gain preamp is more likely to overload than a preamp with less gain. It's likely that your moving the antenna caused another unknown signal to drop in signal strength, hence reducing the overload caused by that signal.

My antenna doesn't have to move in order to switch out the pre-amps, I left both pre-amps physically mounted on the mast and simply swaped the lines. Additionally, the signal strength on the other channels did not change much at all. (maybe they lost a point or two, but that could be just random. KABC lost 20 points

3.) I doubt that it was multipath to start with. See #2. The fact that KABC-DT got much worse with a higher gain preamp is a strong indication that your preamps are overloaded.

So do you think I have too much of a signal coming in on that channel?
Do you think an attenuator for that frequency will help?

The likely candidate for the unknown signal is KVCR; analog 24, digital 26.

Can you please elaborate on this?
please feel free to get technical.

Thanks for you help

 

[Tower Guy]

Towerguy... thanks for the feedback!


Can you please elaborate on this?
please feel free to get technical.

Thanks for you help

I'm guessing because your location is not explicit, but here's my thinking. (You may PM me if you are willing to devulge your address.)

KVCR on channels 24 and 26 needs to be attenuated before the preamp. You could do this with a single Jointenna for channel 25. (tuned halfway between 24 and 26) The Jointenna would be mounted between the antenna and the preamp. The input for the channel 25 antenna would be connected to a 75 ohm termination.

You probably won't be able to see KVCR with this set-up. If you wanted to do so, a second Jointenna on channel 26 and a second smaller antenna aimed at KVCR-DT could be added after the preamp.

Perhaps another antenna model would place KVCR in a null when it is aimed at Mt. Wilson.

Another way to eliminate one signal is to stack two antennas horizontally such that the signals from the front add, (in phase) but the inteferring signals subtract. (out of phase) Notice the directions and depths of the nulls in this configuration of Channel Master 4228's. http://www.hdtvprimer.com/ANTENNAS/16bay.html
To design that type of installation your exact location would be needed. The nulls can be steered somewhat by changing the horizontal distance between the antennas. You can calculate the ideal spacing using trig functions. The out of phase condition can be met with a 180 or 540 degree phase shift. Theoretically, 900 degrees would work too, but the antennas would be excessively spaced. When you do the math remember that the wavelength is different on channel 26 than channel 53. The out of phase condition needs to be on channel 24/26.

I have looked for a detailed explanation of this method on-line but have not been able to find it. I have actually done this myself so I know that it works.

My application was on a hilltop near Utica, NY. Channel 13 in Albany could be seen with the antenna aimed East, the audio from channel 13 in Rochester could be heard when aimed West. Two yagi antennas stacked about 2 wavelengths apart could get either 13 depending on aiming.

 

[Cokeswigga]

Lemme see if I have this correct
You are proposing two solutions:

1.) use a terminated jointenna to Attenuate channel 24-26 (you think this is the culprit channel

2.) using some advanced antenna stacking and/or selection the resulting desctructive interference will "attenuate" channels 24-26

can you elborate as to why you think the channel 24-26 transmission is the problem

Am I correct in guessing that you think that KVCR (24 and 26) is being picked up by the antenna (off axis) and is interferring with KABC (53)

 

[Cokeswigga]

I found the spec sheet for my attenna, there does not appear to be any significant off-axis lobes

http://www.winegard.com/offair/pdf/HD9095P.pdf

 

[gdarwin]

I use the same antenna. I have found it works best without a pre-amp. I have it feeding 4 receivers without a problem. Try without the amp to see what happens.

 

[Cokeswigga]

I did try it and it works great without the preamp.... thanks everyone

I am still intersted in entertaining ideas on improving signal strength, as sometimes during bad weather my signals drop down in the 60's where it pixelates and loses signal.

Do you think antenna stacking will cause overload

 

[Jim5506]

Perhaps your pre-amp was too strong for the tuner(s). Might try a Winegard HDP-269, only 12 dB with high overload resistance.

Stacking identical antennas gains you 3dB at best.

 

[lunkie]

Wondering what the signal strenght readings are without the preamp? Moving the antenna up / down a couple of feet (if possible) could help. Also if you go to the Fcc web site "http://www.fcc.gov/mb/audio/includes/78-mapinfo.htm" click the "tv query" link, read the directions carefully for filling out the form, it will give you a wealth of info for each station call sign you enter. Check how much xmitter power each dtv station is using and it's footprint. the power output and radiation patterns of each station may vary and could explain the differences.

 

[Rick0725]

I have been experimenting with the same issue as above ongoing for several months. jointennas as traps, special made traps, various preamps and distribution amps.

but first, the general sign of overload is signal strength going down as you point towards the tower and going higher as you point away and signal level going down various amounts on different channels.

I have an issue where ch 24/25 interferes with ch14 which is of lower power in an amplified setup. when ch 24/25 goes off the air the issue on 14 goes away. the interference also affects others channels in the uhf spectrum and mostly weak/low power...ch 22, 35,40,60 come to mind.

-traps did not help the situation. there were too many points of interfering channel ingress and could not filter every point.

-lower gain high output preamp helped the situation (hdp-269)

-bypassing vhf, fm, and only amplifying uhf also helped.

-just ordered a uhf band pass filter and will place it before the hdp 269 to see if it helps the situation.

the issue is most likely over amplification worsening the effects of co channel interferences.

trapping will not necessarily improve the situation as you like and would be trial and error.

I am still intersted in entertaining ideas on improving signal strength, as sometimes during bad weather my signals drop down in the 60's where it pixelates and loses signal.

my suggestion would be using an hdp 269 preamp of lower gain and high overload tolerance amplifying uhf and passing vhf/fm. the ap4700 may be ok but the unit has higher gain and would be a risk. I tried the ap 4700 here and had to punt and go back to the hdp269 and amplifying only uhf.

 

[Cokeswigga]

Wondering what the signal strenght readings are without the preamp? Moving the antenna up / down a couple of feet (if possible) could help. Also if you go to the Fcc web site "http://www.fcc.gov/mb/audio/includes/78-mapinfo.htm" click the "tv query" link, read the directions carefully for filling out the form, it will give you a wealth of info for each station call sign you enter. Check how much xmitter power each dtv station is using and it's footprint. the power output and radiation patterns of each station may vary and could explain the differences.

My signal strengths without the pre-amp were similar to those of those with the AP-4700.

THe AP-4800 were lower all around

This is why I elected to remove the pre-amp from the antenna.

 

[lunkie]

Sounds like your antenna is doing a good job at pulling the sations in for being 70 miles out. Just for fun I went to the fcc web site to look at the xmitters, interesting info. KABC runs 182kw, KCBS runs 469 kw, KNBC runs 665 kw and KTTV runs 1000kw, all DTV. Although all are on Mt Wilson the heights vary a great deal, KABC is about the lowest, in height and power. There may be a reflection issue causing some signal canceling. If you can rotate your antenna and pick up KABC off a mountain, well??? With uhf antennas just changing position a few feet can make a big difference, good or bad. Is anyone else in your area trying to watch OTA DTV. Might ask them about their signal quality. Otherwise I'd say your sytem is doing an outstanding job for being 70 miles out, and you can overload the system with a preamp to boot!

 

[Cokeswigga]

Sounds like your antenna is doing a good job at pulling the sations in for being 70 miles out. Just for fun I went to the fcc web site to look at the xmitters, interesting info. KABC runs 182kw, KCBS runs 469 kw, KNBC runs 665 kw and KTTV runs 1000kw, all DTV. Although all are on Mt Wilson the heights vary a great deal, KABC is about the lowest, in height and power. There may be a reflection issue causing some signal canceling. If you can rotate your antenna and pick up KABC off a mountain, well??? With uhf antennas just changing position a few feet can make a big difference, good or bad. Is anyone else in your area trying to watch OTA DTV. Might ask them about their signal quality. Otherwise I'd say your sytem is doing an outstanding job for being 70 miles out, and you can overload the system with a preamp to boot!

yeah I guess I shouldn't complain, I have a lot of things going for me:

1.) LA has all their transmitters in the same place
2.) There are pretty strong
3.) they are high up
4.) I live on a hill
5.) I can get all the channels


No one else in my area has an antenna, so I don't know.


I'm just a tech junkie, and it's interesting to me

I did play with the antenna a lot when I first set it up.
raising it made a HUGE difference from 0' above the roof to 10' above the roof was awesome!