I: [amsat-bb] 23cm TX converters with 435 MHz IF

["i8cvs" <domenico.i8cvs@xxxxxx>]

----- Original Message -----
From: i8cvs <domenico.i8cvs@tin.it>
To: John P. Toscano <tosca005@tc.umn.edu>; Wayne Estes W9AE
<w9ae@earthlink.net>
Cc: AMSAT-BB <amsat-bb@amsat.org>
Sent: Tuesday, April 02, 2002 3:41 PM
Subject: R: [amsat-bb] 23cm TX converters with 435 MHz IF


>
> ----- Original Message -----
> From: John P. Toscano <tosca005@tc.umn.edu>
> To: Wayne Estes W9AE <w9ae@earthlink.net>
> Cc: <amsat-bb@AMSAT.Org>
> Sent: Tuesday, April 02, 2002 8:24 AM
> Subject: Re: [amsat-bb] 23cm TX converters with 435 MHz IF
>
>
> > Wayne Estes W9AE wrote:
> >
> > > I'm looking for commercially made (or kit) 23cm TX converters that
> > > use a 435 MHz IF.  The only one I can find is the Kuhne MKU13OTX
> > > with the 70IF option . . .
> >
> > That's the only one I've come across in my searching.  I decided to go
> > with a Down East Microwave 1268 transmitting converter with a 28 MHz
> > IF.  Their web site only says it may be a future product, but I spoke
> > with them on the phone recently and they are building one for me, so
> > I guess the future has arrived.
> >
> > The 28 MHz IF will work fine with my FT-847 and not interfere with
> > my MMDS downconverter at 122 MHz (on the 2 meter antenna connector).
> > Of course, if you are using a 2M/70cm only satellite radio, such as
> > one of the Icoms (820, 821, 910), that may not work for you.
> >
> > 73 de KB0ZEV
>
> Hi KB0ZEV,
>
> You must be very careful using 28-30 MHz IF for a transmit converter
> 1968 -1970 MHz because the image falls into 1268 - (28 x 2 ) = 1212 MHz
> and unless you have a very sharp interdigital filter after conversion you
> will get a lot of power at 1212 MHz in to the antenna.
>
> 1212 MHz is allowed to Aeronautical Navigation Services and it is possible
> to interfere with it.
>
> 28-30 MHz IF for 23 cm was widely used in Europe 25 years ago
hard-filtering
> the image after convertion but  28 MHz IF was abandoned in favour of
> 144 MHz because using such IF the image falls in to 1268-( 144 x 2 )=980
MHz
> wich requires less filtering after convertion to reject it from the
antenna.
>
> 73" de i8CVS Domenico
>

In addition to the above:

Using 28-30 MHz IF for a transmit converter 1268-1270 MHz the LO (local
oscillator ) is 1268-28= 1240 MHz and it is very difficult to reject it from
the output by almost 30 dB unless very sharp filters are used after mixing.

The unwanted image frequency at 1212 MHz and the LO at 1240 MHz to be
removed from the 1268 MHz wanted output make the 28-30 MHz  IF
inconvenient.

73" de i8CVS Domenico


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