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
help.
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
52.525mhz
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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