[linrad] RE:WSE RX2500 Tx control?

[Leif Asbrink <leif.asbrink@xxxxxxxxxxxxxxxxxxxx]

Hi Stan,

> In TX mode, all RX lines should be isolated with a mechanical relay, as 
> you suggest.  Or with a PIN diode (relay) as Leif suggests.
> Also consider using  a quality double shielded coaxial cable as jumpers, 
> between the LINRAD hardware boxes, such as RG-223.
This is not always necessary.

Linrad allows you to use a separate antenna for receiving and you may
have the receiver running while transmitting. This is quite fun if
you work a distant FM repeater. You can have a couple of hundred watts
to a yagi and connect one of the Linrad rx inputs to this yagi while
you connect the other rx input to another yagi that points in the same
direction. The isolation is easily 40 or 50 dB and you can hear your
own voice back from the repeater even if it is hundred km away or more.
You will notice comments made by others while you are transmitting 
and giving appropriate answers is a bit unexpected..........

Checking what others do while your CQ machine is transmitting a
1 minute CQ can be very helpful in VHF contesting. Another application
for two antennas while you use only one of them for transmit.

When receiving, the Linrad adaptive polarisation will become an
adaptive lobe forming that will give a 3 dB S/N advantage over 
a single antenna (if both antennas are equal)

The only requirement is that you protect the WSE input from excessive
power that could destroy the input amplifier. I have not really tested
at what power level the input transistors fail for the RX144 and by
what mechanism but the safe power level should be far above +10 dBm.
There will be a specificaton when I have evaluated the performance
of the first 25 units.

The RX144 needs a preamplifier. You need a relay that protects the
preamplifier from the tx when using the same antenna for rx and tx.
That is all.

Until Linrad has a mute input you may want to put a simple relay
in the 2.5 MHz line(s) to put the RX2500 input to ground while 
transmitting in order to not hear your own transmission.
Another simple relay in the 10.7 MHz line(s) will provide
much more isolation if you need it. An inductor across the 
relay can be used to balance the relay capacitance so you can
get an extremely high isolation from a single relay.

73

Leif / SM5BSZ



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