[Elecraft] K3 front-end protection

[wayne burdick]

Hi Toby,

[NOTE: I'm so busy that I'm answering about one e-mail a day, now, and 
yours is it  :)  Normally someone else will answer, or the answers will 
end up in the FAQ later on.]


> 1) A friend of mine with a big 160m station killed his RX front end 
> because too much power was coming back on his beverages and the rig's 
> RX antenna input was not grounded / disconnected during transmission 
> by the transceiver.
>
> Are the K3 antenna inputs which might be used for RX only antennas 
> protected against too much power coming back via the RX antenna?

All antenna ports have gas-discharge tubes, and the RX-only ports also 
have carrier-operated relays.

We also monitor the SWR bridge in receive mode (forward/reflected 
power). If a signal large enough to cause front-end damage appears in 
the main T-R path (a "reverse transmit" condition), we quickly open the 
PIN diode path to the receiver, typically in less than 1 ms. The path 
will recover equally fast when the huge external signal disappears. 
Obviously this situation is to be avoided, which is why such stations 
often use external band-pass filters.


> 2) At our contest QTH when we work multi between some of the antennas 
> we also have a lot of power coming back - roughly 20W in the worst 
> case combination of beams and bands (without the extra band passes).
>
> How strong is the RX front end of the K3? How much power can it handle 
> without releasing its smoke?

See above. At a certain power level the RX path will be opened (and the 
audio muted) to avoid exposing the preamp, mixer, and down-stream 
stages to multi-watt signals.

73,
Wayne
N6KR

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