The harmonics are not just VHF, they are HF. If you are on 7 MHz the TR switch will generate 14, 21, 28, and so on.?
I'm not saying that is a problem that will "bite" everyone, but it will certainly be there. I forgot exactly what I measured but this is even a problem when solid state diodes are used to generate voltage for relay transfers and other things.
When the grid is rectifying RF the harmonics from the clipped waveform couple directly back via C2 into the transmission line. Whether someone notices a problem depends on how well the antenna radiates a bothersome harmonic.
As for the output voltage, every tube radio I have seen (and many solid states) would take that okay. It could be reduced if necessary.? ?
73 Tom
|
Thanks, Tom!
?
I am encouraged to know I should be OK with the 3.5V to the RX. As I can increase my TX output to 20 watts, that should make the RX even happier by cutting off a bit more signal than 10 watts.
?
As I'm not overly excited about making the bias changes you mentioned, I think I'll wrap it all back up and enjoy what's left of Novice Rig Roundup!
?
Also, I do run a Drake low pass filter in line after the TR switch.? I probably have the world's biggest collection of low pass filters, so it is good to get some use out of at least one of them.
?
I am so happy you took the time to comment here, Tom.? Thanks again.
?
73,
Jeff
W8KZW
|
The capacitors will not be perfect, they will have leakage. Usually it is a slow-charge leakage. Some years ago, probably the 1980s when I was doing a QSK switch for Heathkit, I looked at the Johnson TR switch. One thing is it puts significant harmonics on the feedline. Anything coupled to the line that clips, unless through a low pass or bandpass filter or properly buffered, will back feed harmonics into the line.? Do not expect this switch to cut off signal to the receiver into fractional volt levels. It cannot do that unless pass through good signals are limited in level, and that will cause increased IMD.? ? ? You said:
? About 10 watts into the TX jack and then on to a 50Ω dummy load from the Antenna jack
? Yields about 9.8 Vpp / 3.5 Vrms? across 50Ω into my scope (thankfully not my receiver)
? 3.5V is only 1/4 watt.? That is perfectly fine on old tube radios. Many solid state radios will take that.? It is unlikely you can change a few simple parts and make this work much different. It has to rectify in the first grid to develop cut off bias.? You might try a hard fixed cathode bias on the second cathode instead of? the cathode resistor. The cathode resistor tends to keep the second stage in conduction. As the cathode current decreases so does the cut off bias on that stage. If you used a resistor from HV and a Zener and held the cathode at a steady positive voltage the rectified negative grid voltage from the first stage would have an easier time getting the second stage into hard cut off.? Looking at the characteristic curves of the 6BL7 and guessing you have 250V anode, you need a net grid bias of -30V to cut the tube off.? You aren't going to get that without some circuitry assistance.? ? If the cathode bias was +10 V fixed you would need an additional -20 on the grid to cut the tube off. This is all just wild guesses in numbers but it is the general idea. Effective tube bias would be negative grid voltage differential to positive cathode fixed bias (even when cut off), so if you had +15 on the cathode and -15 on the grid you would have an effective bias of 30 volts.? The problem using a fixed cathode resistor in both stages is as the plate current drops from adding negative grid bias, the cathode positive goes away.? ?
|
Re: WTB - Johnson Signal Sentry
Hello Mike. I have one but have never tried to connect it.? There are a few little dings in the paint, but overall, it looks pretty good.? I can send a few photos if you like.
73, Russ. KW6T
I am looking for a Johnson Signal Sentry, Part No. 250-25.
?
Thanks!
Mike Harmon, WB0LDJ
mharmon at att dot net
|
Re: Free for USPS Postage, Valiant 1 panel meter
toggle quoted message
Show quoted text
Hello ?? Free for USPS Postage, probably Medium Flat rate box, to the lower 48.Insured. Let us know how much insurance you need for this meter.
We use lots of bubble wrap !!
This meter is not tested. Known Issues: Top edge of the movement housing has been chipped ( someone tried to remove the meter cover with a crowbar). ??? Movement SEEMS free needle movement but, as noted, not tested full scale.
Photo available
Thank You
Ashley
?
?
Thank You
Kiss-Electronics
Ms Ashley Hall
183 N 5th PL.
Cornelius, Oregon
97113
?
?
W7DUZ
?
?
On Wednesday, January 1, 2025 at 05:30:47 AM PST, Group Notification < [email protected]> wrote:
|
Re: Free for USPS Postage, Valiant 1 panel meter
Hello ?? Free for USPS Postage, probably Medium Flat rate box, to the lower 48.Insured. Let us know how much insurance you need for this meter.
We use lots of bubble wrap !!
This meter is not tested. Known Issues: Top edge of the movement housing has been chipped ( someone tried to remove the meter cover with a crowbar). ??? Movement SEEMS free needle movement but, as noted, not tested full scale.
Photo available
Thank You
Ashley
?
?
Thank You
Kiss-Electronics
Ms Ashley Hall
183 N 5th PL.
Cornelius, Oregon
97113
?
?
W7DUZ
?
?
|
Update:
?
The output of the TR switch to the receiver is a bit more manageable driving it with 30 watts (see photo) than with the 10 watts I ran in my previous post:
?
?
Assuming the maximum safe input to my tube-type receiver is +10 dBm, now -13 dBm should be OK.
?
But I was hoping to use my TR switch with my homebrew 10W rig. Am I wrong to think that increasing R1 would move the bias to drive V1 to turn off output to the receiver at a lower transmit power level?
?
?
Jeff
?
?
|
WTB - Johnson Signal Sentry
I am looking for a Johnson Signal Sentry, Part No. 250-25.
?
Thanks!
Mike Harmon, WB0LDJ
mharmon at att dot net
|
Work to be done ...
?
? About 10 watts into the TX jack and then on to a 50Ω dummy load from the Antenna jack
? Yields about 9.8 Vpp / 3.5 Vrms? across 50Ω into my scope (thankfully not my receiver)
?
Any suggestions? The filter caps (C12) are new. I guess I could live with the waveform, but not the amplitude.
Jeff
W8KZW
|
Johnson Viking Valliant 1 For Sale
For Sale: Johnson Viking Valiant 1
?
? ? ?This radio is in good overall shape and appears to be complete. ?It is untested.?? Condition is commensurate with age with some “patina”, especially on the rear panel.?? All knobs move easily.? It has been in dry storage for 10+ years.
?
? ? ?There appears to be extra switch on the front panel placed there by the prior owner.? Additionally, there appears to be one 6-pin tube missing, and another was replaced by what appears to be an R/C network.
??
? ? Because of the above, the radio is being sold for “parts-only”, although I believe that it would be a very good base for a high-fidelity AM transmitter.?
?
? ?Asking $75.00, pick-up or meet-up in Metro-west Boston. ?Other delivery and meet -up arrangements are possible.? I would like to see it go to a good home.?
?
73,
Gene K1NR
|
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
|
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
|
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.
|
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.
|
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.
|
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.
|
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.
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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@...
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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.
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Hi, Mike,
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I share your thoughts.
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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.
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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.
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73,
Jeff
W8KZW
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Thanks for the reply, Mike.
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Both sections of C12 were horrible. I had restuffed the can with new caps which explains the OPEN and supports your theory.
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Jeff
W8KZW
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Russ Williams
Sully - KE0RKM
Mike Langner