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Re: [RFI] Low pass filter opinions

To: aa5jg@fidmail.com, rfi@contesting.com
Subject: Re: [RFI] Low pass filter opinions
From: Jimk8mr@aol.com
Date: Tue, 11 Jan 2011 21:21:47 EST
List-post: <rfi@contesting.com">mailto:rfi@contesting.com>

Do you actually have TVI to over the air TV stations? 
Since the digital transition in 2009, there are extremely few low VHF TV  
stations (CH 2-6, 54-88 MHz) on the air. Maybe 25% of the stations are on 
high  VHF (CH 7-13, 174-216 MHz).
Do you have stations that freeze up or go black when you transmit? If not,  
no problem. Squiggly lines and the like from the days of old are a thing of 
 the past with digital TV.
If you are getting into cable TV, that's another story.  It's either a  bad 
cable system where outside signals are leaking into the cable system  
(shouldn't happen) or fundamental overload which a LP filter will do nothing to 
We've come a long way from the 60's where a six meter transmitter used the  
6th harmonic of an 8 MHz crystal ( or 8th of a 6 MHz crystal) and you then 
had  to filter out the 7th or 9th harmonic from that crystal before your ham 
signal  hit your antenna.
73  -  Jim   K8MR
In a message dated 1/11/2011 8:49:28 P.M. Eastern Standard Time,  
aa5jg@fidmail.com writes:

What  have list members found to be the best low pass filters to prevent 
TVI?   I currently have a Drake TV-1000 in line but that allows RF up to 
52mhz, and  actually above that because I have used it successfully on 
for 6m  FM.  Today I borrowed a Kenwood LF-30A from a friend. I can't find 
too  many specs on it other than it has 90db of attenuation above 90mhz.  It  
didn't make any difference compared to my Drake.  I was thinking that it  
might do better since it should have a lower cutoff frequency.

I see  that Drake also made a TV3300 filter that is rated at 80db above 
41mhz.   And the ICE filters get good reviews on eham.net.  So, any opinions as 
to  what low pass filters work best?

73s John  AA5JG

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