View Single Post
Old 6-Apr-2019, 12:57 AM   #6
rabbit73
Retired A/V Tech
 
Join Date: Aug 2012
Location: S.E. VA
Posts: 2,550
Quote:
Originally Posted by Johnsonbrits View Post
Both Fox Channel 10 (transmits on real channel 7 VHF-High) and PBS KAET Channel 8 (transmits on real Channel 3 VHF-Low) transmitters are located at Porter Mountain about 8 miles away. Due to HOA requirements the antenna is installed in the attic at 115 degrees azimuth towards Porter Mountain.

http://www.tvfool.com/?option=com_wr...903872956fdaf7

I probably went over the top and bought/installed a Winegard 8200U in the attic together with (from memory) a Channel Master Pre-Amp. I get good reception with FOX on real channel 7 but can only occasionally lock into PBS on real channel 3.
Hello, Peter; welcome to the forum.

You need some kind of antenna for K03FB on VHF-Low channel 3. There aren't many choices; the 8200 was a good choice.

The signals will be attenuated by the attic location, but if you can receive K07OJ that is running only 33 watts ERP, you should be able to receive K03FB running 300 watts ERP.

Quote:
While performing physical checks of the antenna I noticed that with the antenna combiner cartridge removed that resistance between the UHF terminals was >200 ohms but for VHF the resistance is <2 ohms which does not seem right to me? Physical inspection (in a very tight attic space) revealed no issues including high resistance between the VHF antenna rods and the central antenna rod used for mounting which is what I expected.
Resistance measurements with a DC ohmmeter are inconclusive when you are working with RF.
Quote:
I may be chasing a "non-issue" since FOX on real channel 7 comes in without problems.
You do have an issue, but we haven't figured it out yet.

There could be a problem with the antenna that allows it to receive 7 better than 3, or it could be, as ADTech mentioned, you have electrical interference on VHF-Low that raises the noise floor and reduces the SNR of 3.

I favor the second possibility because I have made noise measurements for indoor antenna locations that indicate much stronger signals are needed on VHF-Low than on VHF-High for good reception. Noise can come from LED and CFL lamps, electric motors, battery chargers, and switchmode power supplies (AC adapter) for laptops.



Quote:
Question: Is there an electrical diagram for the Winegard 8200 antenna available?
Not that I know of.

Quote:
Lastly, I've read that a Pre-amp does not help for VHF-Low channels and would do better with it removed? Thoughts?
On VHF-Low, a preamp makes the signal and the noise stronger, so you end up right where you started with no improvement.

Try it.

Which CM preamp are you using?
__________________
If you can not measure it, you can not improve it.
Lord Kelvin, 1883
http://www.megalithia.com/elect/aeri...ttpoorman.html

Last edited by rabbit73; 6-Apr-2019 at 4:07 PM.
rabbit73 is offline   Reply With Quote