|
Hi Folks,
?
I don't expect any of you to waste a lot of brain cells on this idea, but I thought I'd run it by you to see if you experts might have an idea for me to try:
?
I'm rebuilding a Johnson Valiant I, and after it's complete, I plan to use it on the 160, 80 and 40 meter bands as an AM/CW station along with my Collins R-388 (51J-3) receiver. ? I've never been a fan of Dow-Key relays as a means of switching antennas from transmit mode to receive mode. Ever since I was a novice back in the Sixties, I've always liked using an electronic TR switch. ?Break-in CW used to be sort of fun back then, and there's no clacking of relays on voice modes. ?The problem with most TR switch designs is the lack of receiver muting capability. ?The best TR switch ever built was the Johnson 250-39, and I have 3 of them! ?They work like a dream for T/R switching, but there's no way to mute the receiver during transmit.
?
The R-388 just happens to have a terminal strip on the back that is connected to a 12 VDC T/R relay inside the receiver. ?When closed, the relay shorts out the front end and kills the B+ to the later stages to mute the receiver. ?This relay could easily be changed to a faster, quieter relay if needed. ?The challenge is - how to activate the relay?
?
Now my brainstorm .... ?The TR switch uses the RF signal to grid-block a 6BL7 dual triode during transmit, and as soon as the transmit signal goes away, the 6BL7 reverts to being a common cathode RF amp. ?Is there any way to use the grid current in the tube to drive a FET or something similar, which could then be used to activate the break-in relay in the receiver? ?I've mulled this idea around for a while, and run it by some local guys, who mostly just did an eye-roll and told me to just use a Dow-Key and put up with the howls from the receiver. ?Well, that's a possibility on CW, but certainly not on voice.
?
Am I crazy? ?Deluded? ?A wishful thinker? ?I know the technology is there - I just don't know how to use it!
I don't know how to attach a PDF of the TR switch schematic, but most of you probably have it anyway.
?
Please tell me what you think.
Thanks!
Mike, WB0LDJ
mharmon at att dot net
|
Mike:
This sounds like a great project.? If
you haven't already done so, you might want to locate a copy of
the Heathkit HW-16 manual and schematic; this was a full QSK
vacuum tube transmitter-receiver which was thought to have
excellent QSK in its day.
Good luck!
Mike N4MWP
On 2/17/25 01:38, Mike Harmon wrote:
toggle quoted message
Show quoted text
Hi Folks,
?
I don't expect any of you to waste a lot of brain cells on
this idea, but I thought I'd run it by you to see if you
experts might have an idea for me to try:
?
I'm rebuilding a Johnson Valiant I, and after it's
complete, I plan to use it on the 160, 80 and 40 meter bands
as an AM/CW station along with my Collins R-388 (51J-3)
receiver. ? I've never been a fan of Dow-Key relays as a means
of switching antennas from transmit mode to receive mode. Ever
since I was a novice back in the Sixties, I've always liked
using an electronic TR switch. ?Break-in CW used to be sort of
fun back then, and there's no clacking of relays on voice
modes. ?The problem with most TR switch designs is the lack of
receiver muting capability. ?The best TR switch ever built was
the Johnson 250-39, and I have 3 of them! ?They work like a
dream for T/R switching, but there's no way to mute the
receiver during transmit.
?
The R-388 just happens to have a terminal strip on the back
that is connected to a 12 VDC T/R relay inside the receiver.
?When closed, the relay shorts out the front end and kills the
B+ to the later stages to mute the receiver. ?This relay could
easily be changed to a faster, quieter relay if needed. ?The
challenge is - how to activate the relay?
?
Now my brainstorm .... ?The TR switch uses the RF signal to
grid-block a 6BL7 dual triode during transmit, and as soon as
the transmit signal goes away, the 6BL7 reverts to being a
common cathode RF amp. ?Is there any way to use the grid
current in the tube to drive a FET or something similar, which
could then be used to activate the break-in relay in the
receiver? ?I've mulled this idea around for a while, and run
it by some local guys, who mostly just did an eye-roll and
told me to just use a Dow-Key and put up with the howls from
the receiver. ?Well, that's a possibility on CW, but certainly
not on voice.
?
Am I crazy? ?Deluded? ?A wishful thinker? ?I know the
technology is there - I just don't know how to use it!
I don't know how to attach a PDF of the TR switch
schematic, but most of you probably have it anyway.
?
Please tell me what you think.
Thanks!
Mike, WB0LDJ
mharmon at att dot net
|
Hi Mike.? I also use a T/R switch with my Johnson Ranger and RME 6900 receiver.? I use my Winkeyer USB to solve the muting problem on CW.? It has a facility to activate a PTT output, designed to turn on an amplifier.? You can adjust the timing of the PTT activation so that the PTT line comes active before the first code element is sent.? I use that PTT line with an external relay to mute the receiver.??
?
73, Floyd - K8AC
|
Hi, Mike,
?
I share your thoughts.
?
I was thinking of rectifying the voltage from the "Probe" port on the TR Switch to turn on a transistor, which would apply a control voltage across a small relay. The relay would switch in a potentiometer in series with the receiver Standby switch to control the allowed RF gain on transmit for monitoring my signal. An R/C circuit with a 2nd variable resistor on "break" to adjust the time constant might act as an "AGC" function for more pleasant listening.
?
I'm actually hoping just to get my homebrew 6DQ6 TX / Drake 2B RX combo working in time for Novice Rig Roundup and Classic Exchange.
?
73,
Jeff
W8KZW
|
Hmmm.
Interesting idea !
Please allow me to share two thoughts.
If you sense voltage across the key rather than at the “Probe” port, you’ll preclude any even small delay in reducing receiver gain.
Using a pot in series with the receiver Standby switch could be problematical depending what receiver you’re using.? Reducing the voltage enough to lower the gain/volume enough could and likely would stop the oscillator(s) in the receiver.
Assuming a tube-type receiver, opening the cathode of the first RF stage if there is one, or if there isn’t one, opening the cathode of one or more IF amplifiers or putting a pot there to allow for just the slightest conduction by the tube(s) likely would do better for you.
In my novice days for a year or so when I was a student with no money to spend on ham radio to speak of, I used a Knight T-50 with an NC-57B.? Lowering the gain of the receiver’s RF stage when the transmitter was keyed worked well for me.
Also, if all the B+ goes through your pot (including the audio output stage) your pot will have to be more than the garden-variety 2-watt carbon pot.
Just musing out loud!
You’re on it!!
73 and Good Luck!
Mike/
________________________________ ? Mike Langner
929 Alameda Road NW
Albuquerque, NM 87114-1901
(505) 898-3212 home/home office
(505) 238-8810 cell
mlangner@...
?
toggle quoted message
Show quoted text
From: [email protected] <[email protected]> On Behalf Of jeffbauman via groups.io
Sent: Tuesday, March 4, 2025 3:23 PM
To: [email protected]
Subject: Re: [EFJohnson-Amateur-Radio] Feasibility Study?? I was thinking of rectifying the voltage from the "Probe" port on the TR Switch to turn on a transistor, which would apply a control voltage across a small relay. The relay would switch in a potentiometer in series with the receiver Standby switch to control the allowed RF gain on transmit for monitoring my signal. An R/C circuit with a 2nd variable resistor on "break" to adjust the time constant might act as an "AGC" function for more pleasant listening. I'm actually hoping just to get my homebrew 6DQ6 TX / Drake 2B RX combo working in time for Novice Rig Roundup and Classic Exchange.
|
Hi Mike,
I’ve been thinking of alternative ways of doing what I wanted to accomplish. ?As constructed, the Collins R-388 receiver has a terminal strip on the rear apron that is connected to a DC relay inside the receiver, in series with a front panel switch labeled “Break-In”. ?When activated, this relay does two things:
1. ? It shorts out the receiver front-end 2. ?It disconnects B+ from the receiver audio circuits.
I have a few 900 V FETs, so I am thinking of using a FET to kill the B+ to the audio circuits. ?The TR switch should take care of the front end.
That way, I could eliminate the relay in the receiver altogether and use a DC signal from the TR switch to trigger the FET. ?Heck, I could even add a bipolar switch to ground the RF input, and then I could be sure that I didn’t have any RF bleed-through from the TR switch.
The DC control line from the TR switch to the receiver would be triggered by the incoming transmit RF.
What do you think?
toggle quoted message
Show quoted text
On Mar 4, 2025, at 17:10, Mike Langner via groups.io <mlangner@...> wrote:
? Hmmm.
Interesting idea !
Please allow me to share two thoughts.
If you sense voltage across the key rather than at the “Probe” port, you’ll preclude any even small delay in reducing receiver gain.
Using a pot in series with the receiver Standby switch could be problematical depending what receiver you’re using.? Reducing the voltage enough to lower the gain/volume enough could and likely would stop the oscillator(s) in the receiver.
Assuming a tube-type receiver, opening the cathode of the first RF stage if there is one, or if there isn’t one, opening the cathode of one or more IF amplifiers or putting a pot there to allow for just the slightest conduction by the tube(s) likely would do better for you.
In my novice days for a year or so when I was a student with no money to spend on ham radio to speak of, I used a Knight T-50 with an NC-57B.? Lowering the gain of the receiver’s RF stage when the transmitter was keyed worked well for me.
Also, if all the B+ goes through your pot (including the audio output stage) your pot will have to be more than the garden-variety 2-watt carbon pot.
Just musing out loud!
You’re on it!!
73 and Good Luck!
Mike/
________________________________ ? Mike Langner
929 Alameda Road NW
Albuquerque, NM 87114-1901
(505) 898-3212 home/home office
(505) 238-8810 cell
mlangner@...
? ? I was thinking of rectifying the voltage from the "Probe" port on the TR Switch to turn on a transistor, which would apply a control voltage across a small relay. The relay would switch in a potentiometer in series with the receiver Standby switch to control the allowed RF gain on transmit for monitoring my signal. An R/C circuit with a 2nd variable resistor on "break" to adjust the time constant might act as an "AGC" function for more pleasant listening. I'm actually hoping just to get my homebrew 6DQ6 TX / Drake 2B RX combo working in time for Novice Rig Roundup and Classic Exchange.
|
For break-in, I’m thinking that opening and closing circuits with the lowest voltage and least current along with not having capacitors that need to discharge to fully mute the receiver would be best.
I’m assuming you don’t want to monitor the transmitter using the receiver at greatly reduced sensitivity/gain during break-in operation
So, shorting out the front end AND killing the audio makes sense. Real world, with a properly operating T-R switch, you shouldn’t have to short the antenna terminals.? I do, however, always place an NE-2 (B2-A) lamp across receiver antenna terminals just for safety.
Shorting out the audio signal to the audio stage might do what you want to accomplish with lots less wear-and-tear on relay contacts, I would think.
I operate with very fast break in – not “semi-break-in,” so I can hear between letters if the other station sends a string of dots to get my attention.
Depending on how fast the break-in operation you prefer operates, what you’re suggesting could work well.
My only concern would be if the relay’s designed for as many operations as break-in creates compared with non-break-in cw or with phone.
Just my thoughts!
Mike/
__________________________________________ ? Mike Langner
929 Alameda Road NW
Albuquerque, NM 87114-1901
(505) 898-3212 home/home office
(505) 238-8810 cell
mlangner@...
?
toggle quoted message
Show quoted text
From: [email protected] <[email protected]> On Behalf Of Mike Harmon
Sent: Wednesday, March 5, 2025 6:10 PM
To: [email protected]
Subject: Re: [EFJohnson-Amateur-Radio] Feasibility Study?? Hi Mike, I’ve been thinking of alternative ways of doing what I wanted to accomplish. ?As constructed, the Collins R-388 receiver has a terminal strip on the rear apron that is connected to a DC relay inside the receiver, in series with a front panel switch labeled “Break-In”. ?When activated, this relay does two things: 1. ? It shorts out the receiver front-end 2. ?It disconnects B+ from the receiver audio circuits. I have a few 900 V FETs, so I am thinking of using a FET to kill the B+ to the audio circuits. ?The TR switch should take care of the front end. That way, I could eliminate the relay in the receiver altogether and use a DC signal from the TR switch to trigger the FET. ?Heck, I could even add a bipolar switch to ground the RF input, and then I could be sure that I didn’t have any RF bleed-through from the TR switch. The DC control line from the TR switch to the receiver would be triggered by the incoming transmit RF.
On Mar 4, 2025, at 17:10, Mike Langner via groups.io <mlangner@...> wrote:
? Hmmm.
Interesting idea !
Please allow me to share two thoughts.
If you sense voltage across the key rather than at the “Probe” port, you’ll preclude any even small delay in reducing receiver gain.
Using a pot in series with the receiver Standby switch could be problematical depending what receiver you’re using.? Reducing the voltage enough to lower the gain/volume enough could and likely would stop the oscillator(s) in the receiver.
Assuming a tube-type receiver, opening the cathode of the first RF stage if there is one, or if there isn’t one, opening the cathode of one or more IF amplifiers or putting a pot there to allow for just the slightest conduction by the tube(s) likely would do better for you.
In my novice days for a year or so when I was a student with no money to spend on ham radio to speak of, I used a Knight T-50 with an NC-57B.? Lowering the gain of the receiver’s RF stage when the transmitter was keyed worked well for me.
Also, if all the B+ goes through your pot (including the audio output stage) your pot will have to be more than the garden-variety 2-watt carbon pot.
Just musing out loud!
You’re on it!!
73 and Good Luck!
Mike/
________________________________ ? Mike Langner
929 Alameda Road NW
Albuquerque, NM 87114-1901
(505) 898-3212 home/home office
(505) 238-8810 cell
mlangner@...
? ? I was thinking of rectifying the voltage from the "Probe" port on the TR Switch to turn on a transistor, which would apply a control voltage across a small relay. The relay would switch in a potentiometer in series with the receiver Standby switch to control the allowed RF gain on transmit for monitoring my signal. An R/C circuit with a 2nd variable resistor on "break" to adjust the time constant might act as an "AGC" function for more pleasant listening. I'm actually hoping just to get my homebrew 6DQ6 TX / Drake 2B RX combo working in time for Novice Rig Roundup and Classic Exchange.
|
OK – noting that you’re thinking of using the HV FET to open the B+, I would ask two questions, please.
If you’re inclined to do it this way, might you consider just killing the audio output state’s screen grid voltage instead??
And I’d wonder about what if the FET fails. If the only place it could send B+ if it shorts is the T-R switch, there’s likely no harm done.? If the circuit you choose could be damaged by the application of B+ in the event of an FET failure, Murphy’s Law says, “if it can fail, it will fail.”? I guess this caution comes from my many trips up New Mexico mountaintops because as Murphy says, the more consequential a failure will be the more likely a failure will take place!
And how fast is the relay ?? Using transistors as switches and eliminating the relay altogether would seem to be the way to go. I think you’re on to something here!!
Just a couple more thoughts!
Mike/
K5MGR
___________________________________________ ? Mike Langner
929 Alameda Road NW
Albuquerque, NM 87114-1901
(505) 898-3212 home/home office
(505) 238-8810 cell
mlangner@...
?
toggle quoted message
Show quoted text
From: [email protected] <[email protected]> On Behalf Of Mike Harmon
Sent: Wednesday, March 5, 2025 6:10 PM
To: [email protected]
Subject: Re: [EFJohnson-Amateur-Radio] Feasibility Study?? Hi Mike, I’ve been thinking of alternative ways of doing what I wanted to accomplish. ?As constructed, the Collins R-388 receiver has a terminal strip on the rear apron that is connected to a DC relay inside the receiver, in series with a front panel switch labeled “Break-In”. ?When activated, this relay does two things: 1. ? It shorts out the receiver front-end 2. ?It disconnects B+ from the receiver audio circuits. I have a few 900 V FETs, so I am thinking of using a FET to kill the B+ to the audio circuits. ?The TR switch should take care of the front end. That way, I could eliminate the relay in the receiver altogether and use a DC signal from the TR switch to trigger the FET. ?Heck, I could even add a bipolar switch to ground the RF input, and then I could be sure that I didn’t have any RF bleed-through from the TR switch. The DC control line from the TR switch to the receiver would be triggered by the incoming transmit RF.
On Mar 4, 2025, at 17:10, Mike Langner via groups.io <mlangner@...> wrote:
? Hmmm.
Interesting idea !
Please allow me to share two thoughts.
If you sense voltage across the key rather than at the “Probe” port, you’ll preclude any even small delay in reducing receiver gain.
Using a pot in series with the receiver Standby switch could be problematical depending what receiver you’re using.? Reducing the voltage enough to lower the gain/volume enough could and likely would stop the oscillator(s) in the receiver.
Assuming a tube-type receiver, opening the cathode of the first RF stage if there is one, or if there isn’t one, opening the cathode of one or more IF amplifiers or putting a pot there to allow for just the slightest conduction by the tube(s) likely would do better for you.
In my novice days for a year or so when I was a student with no money to spend on ham radio to speak of, I used a Knight T-50 with an NC-57B.? Lowering the gain of the receiver’s RF stage when the transmitter was keyed worked well for me.
Also, if all the B+ goes through your pot (including the audio output stage) your pot will have to be more than the garden-variety 2-watt carbon pot.
Just musing out loud!
You’re on it!!
73 and Good Luck!
Mike/
________________________________ ? Mike Langner
929 Alameda Road NW
Albuquerque, NM 87114-1901
(505) 898-3212 home/home office
(505) 238-8810 cell
mlangner@...
? ? I was thinking of rectifying the voltage from the "Probe" port on the TR Switch to turn on a transistor, which would apply a control voltage across a small relay. The relay would switch in a potentiometer in series with the receiver Standby switch to control the allowed RF gain on transmit for monitoring my signal. An R/C circuit with a 2nd variable resistor on "break" to adjust the time constant might act as an "AGC" function for more pleasant listening. I'm actually hoping just to get my homebrew 6DQ6 TX / Drake 2B RX combo working in time for Novice Rig Roundup and Classic Exchange.
|
Mike,
Have you ever heard of a Johnson Signal Sentry? ?I just found out about them today, and the operation sounds intriguing. ?Apparently, the gadget mutes the receiver during transmit and sends an audio “sidetone” to the phones or speaker.
I’ve never used one or even seen one, but now I’m going to try to find one to check it out. ?I’m not a rabid CW op (I just barely managed to pass the Extra Class CW test years ago), but I like the concept of QSK.
Actually, I’ve been licensed since 1968, but haven’t been on CW for years. ?I spend way more time at the bench building or repairing gear.
I’m currently in the process of “re-kitting” a Johnson Valiant I that I plan to use as an AM/CW rig on 160/80/40m with my Collins R-388 receiver.
I just love to tinker and build things, and the QSK project is just a challenge for my engineering expertise!
Wish me luck! 73, Mike, WB0LDJi
toggle quoted message
Show quoted text
On Mar 5, 2025, at 19:49, Mike Langner via groups.io <mlangner@...> wrote:
? OK – noting that you’re thinking of using the HV FET to open the B+, I would ask two questions, please.
If you’re inclined to do it this way, might you consider just killing the audio output state’s screen grid voltage instead??
And I’d wonder about what if the FET fails. If the only place it could send B+ if it shorts is the T-R switch, there’s likely no harm done.? If the circuit you choose could be damaged by the application of B+ in the event of an FET failure, Murphy’s Law says, “if it can fail, it will fail.”? I guess this caution comes from my many trips up New Mexico mountaintops because as Murphy says, the more consequential a failure will be the more likely a failure will take place!
And how fast is the relay ?? Using transistors as switches and eliminating the relay altogether would seem to be the way to go. I think you’re on to something here!!
Just a couple more thoughts!
Mike/
K5MGR
___________________________________________ ? Mike Langner
929 Alameda Road NW
Albuquerque, NM 87114-1901
(505) 898-3212 home/home office
(505) 238-8810 cell
mlangner@...
? ? Hi Mike, I’ve been thinking of alternative ways of doing what I wanted to accomplish. ?As constructed, the Collins R-388 receiver has a terminal strip on the rear apron that is connected to a DC relay inside the receiver, in series with a front panel switch labeled “Break-In”. ?When activated, this relay does two things: 1. ? It shorts out the receiver front-end 2. ?It disconnects B+ from the receiver audio circuits. I have a few 900 V FETs, so I am thinking of using a FET to kill the B+ to the audio circuits. ?The TR switch should take care of the front end. That way, I could eliminate the relay in the receiver altogether and use a DC signal from the TR switch to trigger the FET. ?Heck, I could even add a bipolar switch to ground the RF input, and then I could be sure that I didn’t have any RF bleed-through from the TR switch. The DC control line from the TR switch to the receiver would be triggered by the incoming transmit RF.
On Mar 4, 2025, at 17:10, Mike Langner via groups.io <mlangner@...> wrote:
? Hmmm.
Interesting idea !
Please allow me to share two thoughts.
If you sense voltage across the key rather than at the “Probe” port, you’ll preclude any even small delay in reducing receiver gain.
Using a pot in series with the receiver Standby switch could be problematical depending what receiver you’re using.? Reducing the voltage enough to lower the gain/volume enough could and likely would stop the oscillator(s) in the receiver.
Assuming a tube-type receiver, opening the cathode of the first RF stage if there is one, or if there isn’t one, opening the cathode of one or more IF amplifiers or putting a pot there to allow for just the slightest conduction by the tube(s) likely would do better for you.
In my novice days for a year or so when I was a student with no money to spend on ham radio to speak of, I used a Knight T-50 with an NC-57B.? Lowering the gain of the receiver’s RF stage when the transmitter was keyed worked well for me.
Also, if all the B+ goes through your pot (including the audio output stage) your pot will have to be more than the garden-variety 2-watt carbon pot.
Just musing out loud!
You’re on it!!
73 and Good Luck!
Mike/
________________________________ ? Mike Langner
929 Alameda Road NW
Albuquerque, NM 87114-1901
(505) 898-3212 home/home office
(505) 238-8810 cell
mlangner@...
? ? I was thinking of rectifying the voltage from the "Probe" port on the TR Switch to turn on a transistor, which would apply a control voltage across a small relay. The relay would switch in a potentiometer in series with the receiver Standby switch to control the allowed RF gain on transmit for monitoring my signal. An R/C circuit with a 2nd variable resistor on "break" to adjust the time constant might act as an "AGC" function for more pleasant listening. I'm actually hoping just to get my homebrew 6DQ6 TX / Drake 2B RX combo working in time for Novice Rig Roundup and Classic Exchange.
|
Could you be talking about the Johnson T/R switch? I have one of those and am in the process of setting up an AM station with a Viking I transmitter and this switch. Right now I am trying to decide which receiver from the era I want to rebuild to go with it. I am laid up right now and unable to run down to the shack to get more info on it but I will attach a schematic here. Unable to access the manual from here.
----- Original Message -----
Date: 03/05/25 21:45 Subject: Re: [EFJohnson-Amateur-Radio] Feasibility Study? Mike,
Have you ever heard of a Johnson Signal Sentry? ?I just found out about them today, and the operation sounds intriguing. ?Apparently, the gadget mutes the receiver during transmit and sends an audio “sidetone” to the phones or speaker.
I’ve never used one or even seen one, but now I’m going to try to find one to check it out. ?I’m not a rabid CW op (I just barely managed to pass the Extra Class CW test years ago), but I like the concept of QSK.
Actually, I’ve been licensed since 1968, but haven’t been on CW for years. ?I spend way more time at the bench building or repairing gear.
I’m currently in the process of “re-kitting” a Johnson Valiant I that I plan to use as an AM/CW rig on 160/80/40m with my Collins R-388 receiver.
I just love to tinker and build things, and the QSK project is just a challenge for my engineering expertise!
Wish me luck! 73, Mike, WB0LDJi
On Mar 5, 2025, at 19:49, Mike Langner via groups.io <mlangner=[email protected]> wrote:
? OK – noting that you’re thinking of using the HV FET to open the B+, I would ask two questions, please.
If you’re inclined to do it this way, might you consider just killing the audio output state’s screen grid voltage instead? ?
And I’d wonder about what if the FET fails. If the only place it could send B+ if it shorts is the T-R switch, there’s likely no harm done. ?If the circuit you choose could be damaged by the application of B+ in the event of an FET failure, Murphy’s Law says, “if it can fail, it will fail.” ?I guess this caution comes from my many trips up New Mexico mountaintops because as Murphy says, the more consequential a failure will be the more likely a failure will take place!
And how fast is the relay ? ?Using transistors as switches and eliminating the relay altogether would seem to be the way to go. I think you’re on to something here!!
Just a couple more thoughts!
Mike/
K5MGR
___________________________________________ Mike Langner
929 Alameda Road NW
Albuquerque, NM 87114-1901
(505) 898-3212 home/home office
(505) 238-8810 cell
mlangner@...
Hi Mike,
I’ve been thinking of alternative ways of doing what I wanted to accomplish. ?As constructed, the Collins R-388 receiver has a terminal strip on the rear apron that is connected to a DC relay inside the receiver, in series with a front panel switch labeled “Break-In”. ?When activated, this relay does two things:
1. ? It shorts out the receiver front-end 2. ?It disconnects B+ from the receiver audio circuits.
I have a few 900 V FETs, so I am thinking of using a FET to kill the B+ to the audio circuits. ?The TR switch should take care of the front end.
That way, I could eliminate the relay in the receiver altogether and use a DC signal from the TR switch to trigger the FET. ?Heck, I could even add a bipolar switch to ground the RF input, and then I could be sure that I didn’t have any RF bleed-through from the TR switch.
The DC control line from the TR switch to the receiver would be triggered by the incoming transmit RF.
On Mar 4, 2025, at 17:10, Mike Langner via groups.io <mlangner@...> wrote:
? Hmmm.
Interesting idea !
Please allow me to share two thoughts.
If you sense voltage across the key rather than at the “Probe” port, you’ll preclude any even small delay in reducing receiver gain.
Using a pot in series with the receiver Standby switch could be problematical depending what receiver you’re using. ?Reducing the voltage enough to lower the gain/volume enough could and likely would stop the oscillator(s) in the receiver.
Assuming a tube-type receiver, opening the cathode of the first RF stage if there is one, or if there isn’t one, opening the cathode of one or more IF amplifiers or putting a pot there to allow for just the slightest conduction by the tube(s) likely would do better for you.
In my novice days for a year or so when I was a student with no money to spend on ham radio to speak of, I used a Knight T-50 with an NC-57B. ?Lowering the gain of the receiver’s RF stage when the transmitter was keyed worked well for me.
Also, if all the B+ goes through your pot (including the audio output stage) your pot will have to be more than the garden-variety 2-watt carbon pot.
Just musing out loud!
You’re on it!!
73 and Good Luck!
Mike/
________________________________ Mike Langner
929 Alameda Road NW
Albuquerque, NM 87114-1901
(505) 898-3212 home/home office
(505) 238-8810 cell
mlangner@...
I was thinking of rectifying the voltage from the "Probe" port on the TR Switch to turn on a transistor, which would apply a control voltage across a small relay. The relay would switch in a potentiometer in series with the receiver Standby switch to control the allowed RF gain on transmit for monitoring my signal. An R/C circuit with a 2nd variable resistor on "break" to adjust the time constant might act as an "AGC" function for more pleasant listening.
I'm actually hoping just to get my homebrew 6DQ6 TX / Drake 2B RX combo working in time for Novice Rig Roundup and Classic Exchange.
|
Anyone contemplating using the EF Johnson T/R
switch with anything other than a tube-type receiver should read
Tom Rauch W8JI's comments:
Not wanting to inadvertently ruin an expensive SDR
receiver,? I designed my own version of an SDR protector,?
drawing from the MFJ and other designs.?? It's worked flawlessly
for a number of years but? there is a 3dB loss due to the
splitter.? For HF use, that's never a problem since the noise
floor is the limiting factor when using any modern receiver.
73, Bob W9RAN
|
Hi Sully ,
No, I have (3) of the Johnson TR switches. ?I’m talking about a device called the Signal Sentry. ?It’s basically a keying monitor, but it has other benefits as well.
I’d like to find one in working condition to experiment with.
73,
toggle quoted message
Show quoted text
On Mar 6, 2025, at 09:42, Robert Nickels via groups.io <ranickels@...> wrote:
?
Anyone contemplating using the EF Johnson T/R
switch with anything other than a tube-type receiver should read
Tom Rauch W8JI's comments:
Not wanting to inadvertently ruin an expensive SDR
receiver,? I designed my own version of an SDR protector,?
drawing from the MFJ and other designs.?? It's worked flawlessly
for a number of years but? there is a 3dB loss due to the
splitter.? For HF use, that's never a problem since the noise
floor is the limiting factor when using any modern receiver.
73, Bob W9RAN
|
Mike Dinolfo
Floyd - K8AC
Mike Langner
Sully - KE0RKM