[amsat-bb] Re: Surplus cavity bandpass filters from the AO-10 era?

i8cvs domenico.i8cvs at tin.it
Wed Apr 27 13:46:31 PDT 2011

----- Original Message -----
From: "Bill Dzurilla" <billdz.geo at yahoo.com>
To: <amsat-bb at amsat.org>
Sent: Wednesday, April 27, 2011 7:00 PM
Subject: [amsat-bb] Surplus cavity bandpass filters from the AO-10 era?

> In attempting to make a list of ham equipment I have owned in the past, I
> recalled with fondness a surplus cavity bandpass filter I used with OSCAR
> 10.  At the time, in the 1980s, these were cheap and quite popular with
> satellite users.  I was living in downtown New Orleans, and the filter,
> which was mounted at the antenna next to the mast-mounted preamp, totally
> eliminated my problems with birdies and local cross-mod.
> Does anyone recall this filter and perhaps have a photo or info?
> 73, Bill NZ5N

Hi Bill, NZ5N

What you describes is exacly what I did for AO-10 and AO-13 mounting between
the 2 meter antenna and the preamplifier input a big passband cavity for FM
repeaters tuned on 145.900 MHz satellite center frequency and another
similar cavity tuned as a notch filter to 145.200 MHz to suck the strong
local signals desensing my receiver due to QRO Hams using high power for
local QSO's in FM.

I still use the above setup to receive VO-52 and OSCAR-7 and it works very
well. In addition I have homemade Norton circuit 2 meter preamplifiers
having high dinamic range and  2 meter convertes using MCL double balanced
mixers having very high -1 dB compression point  to reduce overload and
intermodulation distorsion from very strong nearby signals.

To show local friends how it was nice to work satellites with the above
setup I remember I was able to receive OSCAR-13 at 145.950 MHz in SSB
and simultaneously  retransmit this signal at 145.200 MHz FM using 10 watt
over another 2 meters antenna on my roof without to desense OSCAR-13

Actually no way to receive satellites in 2 meters band using a commercial
receivers or tranceivers here in the bay of Naples wich is full of powerfull
FM users ! !

73" de

i8CVS Domenico

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