[Elecraft] RX Ant K3 Preamp vs External Preamp

[Edward R Cole]

Indeed!

Most eme'rs encounter this issue some point in their operation.

I started out on 144-MHz with only 100w on CW.  Then began use of 
digital in 2003.  But it was not until I started running above 800w 
in 2011 that I began to see preamp failure.  I like my preamps to not 
see RF over 0 dBm (1mw) so that implies the need for 61.8 dB 
isolation if running 1500w.  Initially I was using a coax relay with 
only 45-dB isolation.  So I upgraded to better relays (spec > 
80-dB).  But there are two other paths for RF to reach the 
preamp:  1) thru the dc power leads (solved by using RG-58 for my 
power leads), 2) poor shielding in coax jumper from relay to preamp 
(solved by using double-shielded RG-142).

I also use a sequencer for controlling relay and amp transfer to 
transmit (to avoid hot-switching the relay).

These are probably good arguments for using the internal preamp in a 
K3S or PR6 at the K3.  Internal TR switching protects them.

73, Ed

but the 6M antenna on which I would use it is within 10 ft of two
antennas with which I run legal limit, and I have concerns that it would
survive up there. :) My compromise is 7/8-in hard line for those
antennas, which minimizes the loss, and thus the advantage of a
mast-mounted preamp.

73, Jim K9YC


73, Ed - KL7UW
   http://www.kl7uw.com
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