[hpsdr] [Hpsdr] Call for Comments - ALEX - Duplex Operation

[Tony Langdon]

At 07:32 AM 7/26/2007, Graham Haddock wrote:

>What kinds of duplex operation are you contemplating?
>
>1.) Simultaneous transmit and receive through two different band
>transverters for satellite communications.

I'm most likely to be doing the above.


>2.) Test equipment mode, ie, VNA or spectrum analyser with tracking
>oscillator.

So useful I'm likely to use this mode too.

>Question:  In duplex satellite type of operation, can we assume that the
>MERCURY and PENELOPE are always on different frequencies? If so, what
>is typical, and specifically, what is the T-R spacing from the viewpoint
>of the
>Mercury and Penelope (not what the antennas see) ?

Unfortunately, because of the bands used in traditional transverters 
and the location of the satellite sub bands, they could be very 
close, for instance:

Mode A - Uplink 145.800 - 146.000 Downlink - 29.300 - 29.500

With the most common 2m transverter (116 Mhz L.O.), this becomes:

Uplink (at transceiver) - 29.800 - 30.000 MHz
Downlink - 29.300 - 29.500

Separation can be anything between 300 kHz and 700 kHz, depending on 
the exact frequencies of the passbands.

Mode B or J - worst case (using two transverters), the frequencies 
can overlap.  This is the case when the 70cm side is in the range 
435.800 - 436.000, also 437.800 - 438.000 is possible (assuming 
transverters designed for a 10m IF in all cases).  These cases 
correspond to an IF of 29.8 - 30.0 MHz (the VHF side is the same as 
for Mode A above).

With some modification to the transverters (i.e. using a different LO 
crystal), these conflicts can be avoided, by moving the IF outside 
the ham bands, which should be practical for Mercury and Penelope.

73 de VK3JED
http://vkradio.com


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