Re: Full QSK for a uBITX

Vince Vielhaber

According to the voltage chart on the next page, that junction is going to have a large negative voltage on it. That would stop the transmit from going to the receiver.


On 08/07/2019 07:35 PM, Jerry Gaffke via Groups.Io wrote:
Here's a manual for the Argosy, T/R switching (and SWR metering) is on
page 51:
The full transmit RF waveform goes through C1, diode D4 ensures the
bottom of that
waveform is at DC ground, diode D3 then rectifies it to create a DC
voltage across C2 that
is equal to the peak-to-peak voltage of the transmitted RF. The notes
then say that this
relatively high DC voltage available during transmit is used to reverse
bias diodes D1 and D2
such that no transmit signal goes through them to the RCV connector
(which then goes into
the receiver front end).

I'm still staring at it, almost have it figured out.
But D1,D2 look to me like they would be forward biased during transmit,
which would not work at all.

Note that the PIN diodes at D1,D2 are called out as 1n4007's.
And that this transceiver works up through 30mhz.

Another thing to note, the final remains connected to the antenna during
shunting some of the receive energy to ground.
Some of the other T/R switches use additional PIN diodes to isolate the
from the antenna during receive.

Jerry, KE7ER

On Wed, Aug 7, 2019 at 01:37 PM, John Seboldt K0JD wrote:

This is quite interesting, with a nice sophisticated full-tilt
switch. Interestingly, the Ten Tec Argosy (50W) derives the high
voltage back bias from the RF itself with some silicon diodes and
filter capacitors, so providing a full high-voltage power supply is
a bit of an overkill.

John K0JD

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