Nate, you're usually on the money with your observations, but I have to disagree here. I think I recall seeing "circuit descriptions" in service manuals which mention low-pass filtering to keep ultrasonics out of audio power amps. If you pick off a signal ahead of the audio PA in a radio, this could be an issue.
It probably wan't such a big deal back when most stuff was built with discrete components, but I was looking into using an LM386 audio amp in an ultrasound project a few years ago, and discovered it would make rated gain at 300 kHz. In short, if the IF frequency is passing from a receiver to a controller, I don't blame either manufacturer. The squelch circuit probably uses a simple high-pass filter. Anything more would be over-engineering for the application, so it's perfectly appropriate to address this through a recommended user mod. 73, Paul, AE4KR ----- Original Message ----- From: Nate Duehr To: Repeater-Builder@yahoogroups.com Sent: Tuesday, June 03, 2008 3:25 PM Subject: Re: [Repeater-Builder] Re: 455khz filter for Mastr II discriminator audio Willis M. Hagler wrote: > Well, I don't have many answers for you. I am new in this field and > trying to learn and am sharing what I have heard from others who claim > to have had this problem with a Mastr II. The gentleman at Pacific > Research who manufactures the controller has write up on this in their > manual but since I'm not the expert here I'm unable to tell if it's > not applicable to the Mastr II without asking the question. Sitting here scratching my head... PR usually does good engineering work, but I'd have to agree with someone else's recent comment. If their squelch circuit even looks at 455 KHz at all, I don't think I'd use their squelch... you've probably done the right thing using a real squelch line from the rig to "fix" the problem you were experiencing. Why would a squelch care about noise that's so high in the spectrum it's RF???? You don't mean 455 *Hz*, do you? Even then... that's also a sucky place to look for receiver noise. Something's wrong there... Nate WY0X
