Amplifier T/R Keying problem

[William Stewart-2]

I have a problem trying to key a "homebrew" amplifier with my K2 (S/N 5251).
I am using the two-transistor T/R circuit from the "Mods" web page, and the
T/R relay pulls in as expected, however there is an annoying "thump" in the
received audio when the T/R returns to the receive state. I am using the
separate receive antenna (Rx) input. If I disconnect the receive antenna
line from the amp, there is no thump. If I trigger the T/R relay driver
circuit manually, there is no thump.  It seems that there is some
interaction between the receiver unmuting and the T/R relay going to the
"receive" state simultaneously that causes this thump. Any experience or
ideas?

 

Thanks,

 

Bill Stewart

WU0R

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[Don Wilhelm-3]

Bill,

I know of no interaction between the K2 RANT and the receiver muting time.

Before looking at the receiver muting, I suggest that you look at the
amplifier T/R relay dropout time first - for instance if there is a sizable
capacitor across the coil (bigger than .001 uf) it may be holding the relay
in too long.

The other thing to look at is your receive antenna.  Test it by simply
disconnecting the receive antenna (with RANT still active) to see if
something associated with the antenna itself is producing the thump.
If the receive antenna is picking up a charge (or has RF energy on it)
during your transmissions, that energy must be dissipated when going back to
the receive state.  You could try adding an RF Choke across the receive
antenna if you do not have one there already.

OTOH, you may just want to circumvent the problem by increasing the 8R HOLD
time in the K2 menu until the thump disapears.

These are only guesses about the probable causes. Should you want to dig
into the exact cause of the thump, you will need would need a dual trace
'scope triggering on the trailing edge of the T/R signal to find out exactly
what is happening.

73,
Don W3FPR

> -----Original Message-----
>
> I have a problem trying to key a "homebrew" amplifier with my K2
> (S/N 5251).
> I am using the two-transistor T/R circuit from the "Mods" web
> page, and the
> T/R relay pulls in as expected, however there is an annoying
> "thump" in the
> received audio when the T/R returns to the receive state. I am using the
> separate receive antenna (Rx) input. If I disconnect the receive antenna
> line from the amp, there is no thump. If I trigger the T/R relay driver
> circuit manually, there is no thump.  It seems that there is some
> interaction between the receiver unmuting and the T/R relay going to the
> "receive" state simultaneously that causes this thump. Any experience or
> ideas?
>
> Bill Stewart
>
> WU0R
>
>

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