Joe,
Did you mean "offset" when you said stability? I'd agree that 1/2, to a
few Hertz would be annoying. In testing here, and as shown in practice,
simple systems sound better if run at about 10 - 20 Hz offset. This
makes the beating more tolerable without being able to be reproduced
(very well) by the listening speaker. This is also why it is nice to
have high pass filtering in the listening receivers. Radios with PL
filters do nicely, something like the Com-Spec TS-64's PL filter works
well. Unfortunately, many made for ham rigs don't have adequate (if
any) high-pass filtering even if the radio has PL decode. Simulcast
Systems are one area that benefit from Total HPF of a PL filter, where
Notch Filtering would do no good for the Simulcast beats in the very low
frequency range; <60 Hz.
Of course, at 10 Hz offset, a few Hz. of instability at each transmitter
could result in something very annoying; as the two drifting
transmitters could come within a few Hz. of one another or worse yet,
zero beat.
I remember one particular instance many years ago where we did testing
of two transmitters that were close together and run at 67 Hz offset.
You could decode this PL tone when you heard both transmitter sites, but
they didn't have HSO's and drifted enough that PL decoding was not reliable.
Kevin Custer
mch wrote:
>To work well, you will need more than 'a few Hz' stability. Even 1/2 Hz
>is very noticable and annoying.
>
>Joe M.
>
>Thomas Oliver wrote:
>
>
>>You will need the three transmitters to have uhso (high stab oscilators) to
>>keep them within a few hz of each other, you will have to delay the audio
>>so all three transmitters transmit the audio at the same time. I do not
>>know what effect the multipath from buildings will have on the recieved
>>signal. I think it is worth a shot.
>>
>>tom n8ies
>>
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