Topband: Single antenna port xcvr but want to employ separate receive antenna

[Lennart Michaelsson]

Hi JC et al, just to add to the comments of JC:
First of all it is a matter of switching timing. Always disconnect a
separate RX antenna and short the rx entry to ground before the TX chain
(with or without amp) starts to operate.
Second: Get rid of any reradiation from the TX antenna which will otherwise
destroy the the reception.
Len
SM7BIC

-----Ursprungligt meddelande-----
Från: Topband [mailto:topband-bounces at contesting.com] För JC N4IS
Skickat: den 13 januari 2014 17:33
Till: 'James Rodenkirch'; 'Top Band Contesting'
Ämne: Re: Topband: Single antenna port xcvr but want to employ separate
receive antenna

Hi James

There are several solutions for a separated receive port. However let me
comment on some details,

1- Small Delta loop. To be a receiver antenna the antenna gain need to be
less than 20 db, why ? simple. Connect a power meter and a 50 ohms load on
the Small  Delta loop and measure how much power is captured from the TX
antenna, I know several guy the burn the RX port on ICOM and YAESU radios
using transmit antennas as receiver and injecting 100W into the RX port when
transmitting with a legal limit amplifier.  Port isolation and RF protection
must be the first concern for any solution. If the antenna used for RX is
resonant on the same TX band , you  can really burn you RX front end. 

2- Switch speed. The receive port need to switch fast than TX port. 20ms is
not enough, most small frame relays switch around 20ms , To play safe it is
necessary < 10 ms. Another thing to consider.

3- The RX antenna only will add some SN if it adds some directivity,
otherwise the attenuator at -20db will  do the same job.

4-  Isolation, on low bands if you have s9+10db noise and only 50 db
isolation between the RX and TX port, the signal from the TX antenna will be
add to you RX signal degrading the signal to noise and reducing side and
back nulls form the RX antenna.

I can list another several reason to the subject but the T/R switch is a
very important part of the receiver system if you want to have some
improvement on the signal noise. 
I sent one RTR-1 to T6LG to use with a good Preamp from KD9SV and a Delta
Flag antenna using twisted pair. Without the RTR-1 the system would not
perform well as it did.

Just my two cents.

Regards
JC
N4IS

-----Original Message-----
From: Topband [mailto:topband-bounces at contesting.com] On Behalf Of James
Rodenkirch
Sent: Monday, January 13, 2014 8:36 AM
To: Top Band Contesting
Subject: Topband: Single antenna port xcvr but want to employ separate
receive antenna

Have my vertical working great and have a small Delta-loop low band receive
antenna BUT the Ten Tec Jupiter doesn't have a separate receive antenna like
a K2, for instance (I borrowed a K2 to try out but the buttons/controls are
to small for me to operate as I have a severe case of peripheral neuropathy,
courtesy of Agent Orange).So, I am up and running and will be in the CQ 160
contest at the end of January but have no means, currently, of switching
rapidly 'tween the top loaded vertical and loop. A T/R switch won't "do it"
for me....so looking at a DX Engineering RTR-1A but sure don't like the
price!!http://www.dxengineering.com/parts/dxe-rtr-1a
Anyone have an RTR-1 or 1A that is excess to their needs and willing to sell
OR have another idea of how I can employ a separate receive antenna when I
have one antenna port?
Thank you, in advance, for any replies....off line replies work for me.
72/73, Jim Rodenkirch K9JWV 		 	   		  
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