On Tuesday 09 Aug 2005 22:11, you wrote:
Hi Dave
> > I have a problem with a really near 430Mz transmitter (my own) that is
> > breaking though to the TV. The Transmitter isn't off tune and as far as I
> > Know or can see, it isn't producing any side transmissions or birdies.
>
> I had similar problems with my 2-meter transmissions affecting all the TVs
> in the house.
>
> The root of the problem was the use of a cheap Radio Shack TV signal
> amplifier and distribution box. The strong local signal was overdriving
> the amplifier (probably a 1- or 2-transistor broadband design) and causing
> it to distort every signal passing through it.
>
> You may be running into a similar problem, even if you don't have a
> separate distribution amplifier. TV tuner circuits are often optimized
> for weak-signal conditions, and may not have a high enough IP3 to hold
> off a strong local signal. This "fundamental overload" can't be cured
> at the transmitter, as you clearly understand - you have to keep the strong
> signal out of the electronics which were being overdriven.
>
> > So, My question is, does anyone know of a really good filter design or
> > commercial filer that will block 430.625 so that it dosn't appear in the
> > downlead to the TV.
>
> You'll need a notch or bandstop filter, or a set of paralleled bandpass
> filters, to allow the TV frequencies through and block the 430 MHz signal.
> A notch or bandstop will probably be the best way to go.
>
> The solution I found (after searching around for quite a while) is
> a notch filter made by the Tin Lee company in Canada. They specialize
> in TV filters of various sorts, and their selection is much richer
> than I was able to find via any local supplier.
Thanks for the quick answer - I will look at the site.
Wonder what the deliver time is to the UK :-)...
>
> The one I bought was one of their CR7 models - a band-stop
> type which knocks out everything from 130 MHz to 175 MHz.
> Mounted right up at the antenna, it does a beautiful job...
> the overload/interference problem has gone away entirely.
>
> I suggest that you contact them at www.tinlee.com, and give them
> the details of the frequency range(s) you want to pass and which
> you wish to notch out. They may have a stock model which will
> do what you want, they have some tunable models, and if all
> else fails I'm sure they can build you a custom trap against
> the frequency you're concerned about.
>
> You could try building a coaxial-trap notch (e.g. a quarter-wave
> open section of coax, or a half-wave shorted section of coax,
> connected in parallel with the feedline) but this might have
> adverse effects on other frequencies.
I did try that route , but unless I was doing it wrong, It didn't seem to have
any effect, so I am down to a notch filter or/and a single channle filter,
these (unless you know) are made so that they only pass the TV channels in my
area (they are setup specifically), but they cost £150 as fas as I know...
>
> 73,
Thanks again
73's
Steve
>
> Dave AE6EO
--
O o
_\_ o
\\/ o\ .
//\___=
''
RHCT 603005411793211
RHCE 804005830215073
Tue, 09 Aug 2005 22:28:50 +0100
22:28:50 up 3:52, 1 user, load average: 2.00, 2.55, 2.43
You have not converted a man because you have silenced him.
-- John Viscount Morley
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