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

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

----- 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


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