[Premium-Rx] 6790 filters

[Michael O'Beirne]

Gents

A propos Bob's email (below) is there any mileage in removing the 455kHz 
filters and fitting them to a HB "piggyback" PCB mounted directly above the 
space formerly occupied by the filters?  One could then incorporate proper 
relay switching and any other frills on the new PCB without trying to modify 
the existing PCB extensively.

Proper relay switching is used for the IF filters of the Marconi H2540 and 
H2541 and the Eddystone 1650 and there is no sign of filter leakage.

I have never experienced dry switching.

I know that DIL relays can be unreliable and they are a pain in the 
posterior in the cramped sub-octave filter unit of the Plessey PR2280.  The 
UK MOD usually specify that a whetting DC current must be applied at about 
5mA to keep the relay contacts in low level signal circuits in good form.

73s
Michael
G8MOB

----- Original Message ----- 
From: "Bob Betts" <rwbetts at sbcglobal.net>
To: <premium-rx at mailman.qth.net>
Sent: Friday, August 17, 2012 3:15 PM
Subject: Re: [Premium-Rx] 6790 filters


Charles:
I agree with that. We have been through that several times with various R&D 
designs.
Depending on the frequencies, filter loop imedances and other variables, 
solid state switching can come with unwanted results. I suppose there are 
some newer diodes that have lower capacitance and other more desirable 
characteristics, but for the most part we have avoided them.
A recent project with headend amps and bandpass filter switching would never 
have passed spec without the use of relays. Admittedly, the requirements 
were kind of tight, but then, that's a good thing...especially when working 
around the front end of a receiver where compromises are not good..

If anyone has any modern data on newer s/s devices or techniques to 
accomplish this kind of switching - I'm am all ears, and would love to learn 
about it.

Bob

.