Bob Spooner wrote:
I have acquired a Johnson T-R switch snip

Hi,
Don't forget to include a low-pass filter
between the electronic TR switch
and the antenna. I got c.w. thumps in my stereo system
when I tried operating without a filter. I assume TVI would
be a problem without a filter, also.

The Johnson TR switch also works well when placed between
a separate receive antenna and the receiver. It actually
has a good noise figure, and provides some receive gain.
It works very nicely with a Collins 51S-1, due to its
50 Ohm output to the receiver. The 51S-1 requires a 50 Ohm
antenna for its front end tuned circuits to work as designed,
so a random length receive antenna can provide disappointing
operation otherwise.

Be careful about burning your hand - the Johnson TR switch
runs hot!

73,
Ed Knobloch

I vaguely recall that some T/R electronic switches added the bandswitch to
eliminate suckout.

73, Colin K7FM

Ive seen it proposed that you connect to the valve anode .via a high
voltage cap ...never tried . looked a bit risky with 3/4 kv of rf ..
but i suppose that would prevent the 'suck out' from the pi tank
cct .. the rx would be looking through the cct , as long as the vlave
was biased off .. not too much noise ?

G ..


On Aug 23, 1:15*am, "COLIN LAMB" wrote:
I vaguely recall that some T/R electronic switches added the bandswitch to
eliminate suckout.

73, *Colin *K7FM

On Wed, 27 Aug 2008, Graham wrote:

Ive seen it proposed that you connect to the valve anode .via a high
voltage cap ...never tried . looked a bit risky with 3/4 kv of rf ..
but i suppose that would prevent the 'suck out' from the pi tank
cct .. the rx would be looking through the cct , as long as the vlave
was biased off .. not too much noise ?

G ..

I thought that was the common form, certainly in homebrew articles
that seems to predominate. Yet, the commercial ones are likely to
be standalone, so one doesn't have to fuss with the transmitter.

I've never used one, and never given it much thought. I thought
the suckout issue was when it was connected to the plate of the
transmitter, but that's more likely because the suckout issue
was a common issue with TR switches, and I was more familiar with
connecting it to the plate of the transmitter's output tube.

One thing, it certainly was not uncommon to see articles where
the TR switch included a stage of amplification and a tuned circuit
of some sort.

Also, when connecting to the plate, they'd use a very small value
capacitor, and one article I just checked said to use an even smaller
value for a higher power transmitter. That's going to cause some sort
of loss, indeed that article mentioned one might need to add a tuned
circuit to the TR switch to compensate for the loss.

MIchael VE2BVW

On Aug 27, 5:19*pm, Michael Black wrote:
On Wed, 27 Aug 2008, Graham wrote:
Ive seen it proposed that you connect to the valve anode .via a high
voltage cap ...never tried . looked a bit risky with 3/4 kv of rf ..
but i suppose that would prevent the 'suck out' from the pi tank
cct .. the rx would be looking through the cct , as long as the vlave
was biased off .. not too much noise ?

G ..

I thought that was the common form, certainly in homebrew articles
that seems to predominate. *Yet, the commercial ones are likely to
be standalone, so one doesn't have to fuss with the transmitter.

I've never used one, and never given it much thought. *I thought
the suckout issue was when it was connected to the plate of the
transmitter, but that's more likely because the suckout issue
was a common issue with TR switches, and I was more familiar with
connecting it to the plate of the transmitter's output tube.

One thing, it certainly was not uncommon to see articles where
the TR switch included a stage of amplification and a tuned circuit
of some sort.

Also, when connecting to the plate, they'd use a very small value
capacitor, and one article I just checked said to use an even smaller
value for a higher power transmitter. *That's going to cause some sort
of loss, indeed that article mentioned one might need to add a tuned
circuit to the TR switch to compensate for the loss.

* * MIchael *VE2BVW

Yes , that was as far as I went , made a dual gate fet t/r switch, but
it needed a tuned cct , did work on the low z side but was down in
gain ...

G ..