[BC] SCA Bandwidth and crosstalk...

[Burt I. Weiner]

First off, I can't imagine the bandwidth of the tank causing the 
"high Frequency" roll off within the SCA itself.  Some tilt, 
maybe.  As far as minimizing the cross talk goes, one of my tricks is 
to remove the modulation from the SCA and under normal main channel 
programming conditions try tuning the transmitter for minimum Main 
Channel to SCA crosstalk.  Basically you are tuning for synchronous 
noise but not just in the main channel world.  You need to do the 
same thing for signals up to 100 kHz.  Grid circuits are particularly 
prone to causing cross talk.  You will most likely trade off a slight 
amount of efficiency for minimum crosstalk.  Be sure that all of the 
tuned circuits are a bit over-coupled in order to get the necessary 
bandwidth.  That should head you in the right direction for a start.

Burt


At 10:00 PM 8/2/2006, you wrote:
>From: wpio fm radio <wpio at gate.net>
>Subject: [BC] Henry Radio 3 KW - blame for SCA crosstalk?
>To: "Broadcasters' Mailing List" <broadcast at radiolists.net>
>Message-ID: <44D178CC.8030509 at gate.net>
>Content-Type: text/plain; charset=ISO-8859-1; format=flowed
>
>We're testing the 92khz subcarrier, and have two disturbing
>symptoms:
>
>1. There is main to sub crosstalk (even with stereo gen off)
>2. It sounds like all the treble highs are being rolled off.
>
>(I know it's 4 KHz tops anyway)
>
>The Henry Transmitters are a one of a kind tank circuit.
>
>Could the Henry be the blame for 1 or 2 above?
>
>RH

Burt I. Weiner Associates
Broadcast Technical Services
Glendale, California  U.S.A.
biwa at earthlink.net
K6OQK