I have acquired a Johnson T-R switch and during testing at 3.5+ MHz. and
about 100W into a good dummy load, with the receive port terminated with 51
ohms I'm seeing an initial level on the order of four volts peak before the
6BL7 shuts off and reduces the level. Is this normal? If not, what is
normal?
Thanks. 73, Bob AD3K

On Aug 20, 9:37*am, "Bob Spooner" wrote:
I have acquired a Johnson T-R switch and during testing at 3.5+ MHz. and
about 100W into a good dummy load, with the receive port terminated with 51
ohms I'm seeing an initial level on the order of four volts peak before the
6BL7 shuts off and reduces the level. *Is this normal? If not, what is
normal?
Thanks. 73, Bob *AD3K

Bob,I haven`t used one of these in years ,But, I think that 4 volts at
rec terminals would be acceptable ..At 4 volts on rec terminals not
enough current would flow to do any damage to the input circuit..High
voltage to rec terminals ,like lightning surges etc are the ones that
do damage.. GL Harold W4PQW

"Bob Spooner" wrote in message
...
I have acquired a Johnson T-R switch and during testing at
3.5+ MHz. and about 100W into a good dummy load, with the
receive port terminated with 51 ohms I'm seeing an initial
level on the order of four volts peak before the 6BL7 shuts
off and reduces the level. Is this normal? If not, what is
normal?
Thanks. 73, Bob AD3K
Are we talking about RF here?


--
---
Richard Knoppow
Los Angeles, CA, USA

Bob,I haven`t used one of these in years ,But, I think that 4 volts at
rec terminals would be acceptable ..At 4 volts on rec terminals not
enough current would flow to do any damage to the input circuit..High
voltage to rec terminals ,like lightning surges etc are the ones that
do damage.. GL Harold W4PQW

Harold, Thanks for your reply. It puts things in perspective. 73, Bob AD3K

"Richard Knoppow" wrote in message
...

Are we talking about RF here?

Yes. I was triggering the scope on the transmit RF and looking at the RF on
the output of the receive port across 51 ohms. 73, Bob AD3K

Bob Spooner wrote:
"Richard Knoppow" wrote in message
...
Are we talking about RF here?

Yes. I was triggering the scope on the transmit RF and looking at the RF on
the output of the receive port across 51 ohms. 73, Bob AD3K



That about +16dBm. Shouldn't do any real harm. Healthy signal but
non-destructive.

Bob Spooner wrote:
I have acquired a Johnson T-R switch and during testing at 3.5+ MHz. and
about 100W into a good dummy load, with the receive port terminated with 51
ohms I'm seeing an initial level on the order of four volts peak before the
6BL7 shuts off and reduces the level. Is this normal? If not, what is
normal?
Thanks. 73, Bob AD3K


Now that you're reassured about receiver safety, please let me know
about your experiences with that Old-timey switch. Years ago, I used
a similar one with my Hallicrafters HT-37 and Drake 2B. I found that
the Xmtr's resonant tank circuit produced a null that went through the
T-R switch, and pulled down the 2B's sensitivity. I eventually
abandoned the Electronic switch for a relay.

Jerry, W9NPI

"afcsman" wrote in message
. ..
Now that you're reassured about receiver safety, please let me know about
your experiences with that Old-timey switch. Years ago, I used a similar
one with my Hallicrafters HT-37 and Drake 2B. I found that the Xmtr's
resonant tank circuit produced a null that went through the T-R switch,
and pulled down the 2B's sensitivity. I eventually abandoned the
Electronic switch for a relay.

Jerry, W9NPI
Jerry,
I've seen references to an article in QST about changing the length of the
coax between the transmitter and the switch when that happens. I used a
homebrew version of the T-R switch in the early to mid 70's with a Valiant
II and HQ-170A and never noticed a problem. But then I don't remember ever
checking to see if the receive sensitivity went up when I detuned the tank
circuit. If I run accross the information about which issue contains the
article giving the analysis, I'll post it here. One thing that can be a
problem when using the T-R switch with modern amplifiers that aren't class C
is that amplifier noise will get into the receiver if the amp isn't biased
off during receive. I've seen this on the scope while doing tests using my
JST-245. I'm planning to use it with a Collins 310B, so noise shouldn't be a
problem.
73, Bob AD3K

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