[NLRS] VHF low pass filters?

[Chris Elmquist]

Another consideration is whether your own TV equipment has any issues.
If you can demonstrate that your own TV is unaffected, then this helps
focus where the problem lies.

The suggestions about preamps are very good.  Many people are using
"digital antennas" which have embedded preamps in the enclosure and
they may not even know it (or know what a preamp is).  The clue is if
there is a power injector on the coax leading to the antenna--  as this
supplies the DC to run the preamp which may be inside the antenna housing.
Often these antennas are flat panel-like assemblies or round radomes--
not traditional yagi style designs.  And they are made pretty cheap and
very likely to suffer saturation from strong, out-of-band RF nearby.

How far out from Shoreview is the problem TV located?  If the TV is
already getting marginal signal, it will be pretty easy for your RF to
swamp it even if your signal is out-of-band.  The TV owner may need to
move up to a higher gain, narrower beam-width antenna (ie, a real yagi)
or at the very least, ensure he is pointing optimally at Shoreview in
order to get stronger signal in the TV band and reject your stuff.

Good luck.  Keep us posted.

Chris N0JCF

On Wednesday (01/02/2013 at 08:40AM -0600), Ed WB0VHF wrote:
> 
> 
> Kirk,
> 
> Another thought would be to check with the League (either or both the web and call) to see what tvi resources they have.
> 
> GL & 73,
> Ed
> WB0VHF
> 
> 
> Sent from my HTC
> 
> ----- Reply message -----
> From: w0zq at aol.com
> Date: Wed, Jan 2, 2013 08:29
> Subject: [NLRS] VHF low pass filters?
> To: <nlrs at mailman.qth.net>
> 
> 
> 
> 
> Tough one Kirk.  Here are my thoughts.
> 
> If you can arrange it, have him watch his TV while your transmit.  
> 
> Questions to ask are:
> 
> Does the interference happen on all channels or just some?   
> If its some, which ones and are these channels still the over-the-air VHF channels .... UHF channels are OK?   This means figuring out where each channel is actually transmitting (freq wise that is)
> If all channels are affected then check to see if his over-the-air UHF antenna has a preamp .... it may be built into the antenna or perhaps he is using an (additional?) external preamp downstream.  You are most likely swamping (blocking) the preamp.  Some of these preamps have adjustable gain .... try turning the gain down if its adjustable.  I have not done this myself, but it may be possible to put a high pass filter between the antenna and the preamp, or the UHF antenna manufacturer may have such an option.  Again, I don't recall where all the over-the-air TV stations are transmitting (in terms of freq) these days.  
> 
> I doubt the problem is on your end so there is not much that you can do other than to try dropping your transmit power to see if there is a threshold that is reasonable ..... for example maybe 400 watts doesn't cause a problem, etc.   
> 
> If the problem is that his antenna preamp is being overloaded, you can point this out to him and suggest that he switches to cable .... more of a sales job here than a technical one.  Again, it most likely not your fault that his powered UHF antenna preamp is of such a design that its easiely overloaded (if that is what it is).
> 
> 73, Jon
> W0ZQ
> 
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-- 
Chris Elmquist