Topics

T/R Switching


Jim, ND9M / VQ9JC
 

As a recent joiner of 4SQRP, I'm looking forward to getting back into building my own stuff. The NS-40 seems to be a popular and well designed rig, and my plan is to use my FT-857 for the RX side. Otherwise, the 857 is my day-to-day rig, and I have to protect it. (For QRP use, I drop the drive down and measure the output on an external wattmeter.)
 
So here's a newbie query from an old time ham (me!) who should know the answer but doesn't: What is everyone else who uses separate TX and RX units doing to mute their RXs when the TXs are doing their thing? A rule of thumb was given me a few days ago that there must be at least 40 dB attenuation to protect the RX front end, but that's also going to depend on what the TX power is to start with.
 
My old Hallicrafters RXs could handle a bit of a pop at QRP levels when I did manual switching. I'm a bit leery however about subjecting the "newfangled" 857 to similar treatment. I never had a Dow key which would've done nicely for the boat anchors, but - assuming I could put my hands on one - would a Dow key with its mechanical relay have fast enough response time to protect the 857's front end?
 
What other alternatives are currently in play?
 
Tks/73,
 
Jim, ND9M / VQ9JC


Rich Fowler <k8meg@...>
 

Hi Jim,

My suggestion would be the 4SQRP Magicbox. It will perform all the magic you want including T/R switching, muting, sidetone, etc. Look for it on our favorite qrp site under kits.

Good luck!
Rich


--- On Wed, 2/13/13, Jim, ND9M / VQ9JC wrote:

From: Jim, ND9M / VQ9JC
Subject: [4sqrp] T/R Switching
To: 4sqrp@...
Date: Wednesday, February 13, 2013, 11:06 AM

 

As a recent joiner of 4SQRP, I'm looking forward to getting back into building my own stuff. The NS-40 seems to be a popular and well designed rig, and my plan is to use my FT-857 for the RX side. Otherwise, the 857 is my day-to-day rig, and I have to protect it. (For QRP use, I drop the drive down and measure the output on an external wattmeter.)
 
So here's a newbie query from an old time ham (me!) who should know the answer but doesn't: What is everyone else who uses separate TX and RX units doing to mute their RXs when the TXs are doing their thing? A rule of thumb was given me a few days ago that there must be at least 40 dB attenuation to protect the RX front end, but that's also going to depend on what the TX power is to start with.
 
My old Hallicrafters RXs could handle a bit of a pop at QRP levels when I did manual switching. I'm a bit leery however about subjecting the "newfangled" 857 to similar treatment. I never had a Dow key which would've done nicely for the boat anchors, but - assuming I could put my hands on one - would a Dow key with its mechanical relay have fast enough response time to protect the 857's front end?
 
What other alternatives are currently in play?
 
Tks/73,
 
Jim, ND9M / VQ9JC


Gary <countyhunterw4gns@...>
 

  Howdy Jim, long time no speak !  I use this and am quiet happy: 
 
 http://www.4sqrp.com/MagicBox.php   Enjoy QRP, it’s loads of fun, and the 4 state people are EXTREMELY nice.
 
Gary-W4GNS
 
 
What other alternatives are currently in play?
 
Tks/73,
 
Jim, ND9M / VQ9JC


Wayne Dillon
 

Hi Jim,
One of the solutions which springs to mind is the "Magic Box" an excellent example of one of the 4SQRP kits, check it out on the website. One other solution I have used in the past is a single transistor driven C/O driving a relay, don't forget to put a couple of back-to-back diodes across the RX input to help limit what the RX sees. I can't guarantee it's safety with the good ole '857 though. There will be others on here who will no doubt offer more accurate and up-to date advice. Do ckeck out the "Magic Box" though, as a standalone solution to T/R switching it's neat.
72/3 es God Bless de Wayne - KC0PMH

On Wed, Feb 13, 2013 at 10:06 AM, Jim, ND9M / VQ9JC <Claryco@...> wrote:
 

As a recent joiner of 4SQRP, I'm looking forward to getting back into building my own stuff. The NS-40 seems to be a popular and well designed rig, and my plan is to use my FT-857 for the RX side. Otherwise, the 857 is my day-to-day rig, and I have to protect it. (For QRP use, I drop the drive down and measure the output on an external wattmeter.)
 
So here's a newbie query from an old time ham (me!) who should know the answer but doesn't: What is everyone else who uses separate TX and RX units doing to mute their RXs when the TXs are doing their thing? A rule of thumb was given me a few days ago that there must be at least 40 dB attenuation to protect the RX front end, but that's also going to depend on what the TX power is to start with.
 
My old Hallicrafters RXs could handle a bit of a pop at QRP levels when I did manual switching. I'm a bit leery however about subjecting the "newfangled" 857 to similar treatment. I never had a Dow key which would've done nicely for the boat anchors, but - assuming I could put my hands on one - would a Dow key with its mechanical relay have fast enough response time to protect the 857's front end?
 
What other alternatives are currently in play?
 
Tks/73,
 
Jim, ND9M / VQ9JC




--
http://www.qsl.net/kc0pmh/   Under construction but please visit anyway.
 
QRP -  EFFICIENCY AND SKILL, NOT POWER. 
 
I'm British by birth but American by CHOICE!

Jesus came to pay a debt He didn't owe because we owe a debt we cannot pay...

The Lord bless you and keep you
The Lord make His face shine upon you, and be gracious unto you
The Lord lift up his contenance upon you and give you peace.

God Bless from Wayne Dillon - KC0PMH

Joshua 24:14-15
2 Cor 5:17
1 Jn 2:17
 

4 State QRP Group NCS - 40m & 160m
4SQRP #95
FPQRP #342 (Flying Pigs QRP Club)
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Nick-WA5BDU
 

Good question.  I do a lot of fooling with different boatanchor matchups.  I built this RF sensing antenna switcher from Solid State Design for the Radio Amateur a few years ago that serves me well.  It has adjustable drop out, so it's semi-break-in.  But no provision for muting so I ride the AF & RF gains.

For little QRP RX and TX boards, I might just use an SPDT toggle switch to swap between TX and RX and maybe get those phones off my ears a bit before transmitting.

But like you said, you'd like to protect a more modern rig.  The old BAs were tough. With some kind of SPDT arrangement whether relay or toggle switch, you're never going to have the TX connected directly into the RX input.  Worst case, slow switching will have the TX deadheaded for a few ms but I don't know that you'd couple excess RF into the receiver doing that.  Maybe if you're on 80 or 40 you can afford to have the preamp off and even a bit of attenuation turned on for an extra measure of protection.  A bandaid fix for sure, I admit.  However, I have a K3 and if it senses excess RF into the receiver, it will start automatically taking such steps.

If your switch or relay had an extra pole, you could use it to ground the RX antenna input during transmit.  That still leaves you with that switching time vulnerability though.  The only thing I can think of for that is some kind of sequencer, like a microcontroller.  Or as others have said:

Something like the magic box would be the Cadillac solution, of course.

72-

Nick, WA5BDU


On 2/13/2013 10:06 AM, Jim, ND9M / VQ9JC wrote:
 

As a recent joiner of 4SQRP, I'm looking forward to getting back into building my own stuff. The NS-40 seems to be a popular and well designed rig, and my plan is to use my FT-857 for the RX side. Otherwise, the 857 is my day-to-day rig, and I have to protect it. (For QRP use, I drop the drive down and measure the output on an external wattmeter.)
 
So here's a newbie query from an old time ham (me!) who should know the answer but doesn't: What is everyone else who uses separate TX and RX units doing to mute their RXs when the TXs are doing their thing? A rule of thumb was given me a few days ago that there must be at least 40 dB attenuation to protect the RX front end, but that's also going to depend on what the TX power is to start with.
 
My old Hallicrafters RXs could handle a bit of a pop at QRP levels when I did manual switching. I'm a bit leery however about subjecting the "newfangled" 857 to similar treatment. I never had a Dow key which would've done nicely for the boat anchors, but - assuming I could put my hands on one - would a Dow key with its mechanical relay have fast enough response time to protect the 857's front end?
 
What other alternatives are currently in play?
 
Tks/73,
 
Jim, ND9M / VQ9JC




Todd K7TFC
 

Jim,

Here's a link to a QSK circuit that uses reed relays. You find find it'll suitt your purpose.


73,

Todd
------------------------------------------------------------------------------------
K7TFC / Medford, Oregon, USA / CN82ni / UTC-8
------------------------------------------------------------------------------------
QRP (CW & SSB) / EmComm / SOTA / Homebrew / Design


On Wed, Feb 13, 2013 at 7:29 PM, Nick-WA5BDU <nick-wa5bdu@...> wrote:
 

Good question.  I do a lot of fooling with different boatanchor matchups.  I built this RF sensing antenna switcher from Solid State Design for the Radio Amateur a few years ago that serves me well.  It has adjustable drop out, so it's semi-break-in.  But no provision for muting so I ride the AF & RF gains.

For little QRP RX and TX boards, I might just use an SPDT toggle switch to swap between TX and RX and maybe get those phones off my ears a bit before transmitting.

But like you said, you'd like to protect a more modern rig.  The old BAs were tough. With some kind of SPDT arrangement whether relay or toggle switch, you're never going to have the TX connected directly into the RX input.  Worst case, slow switching will have the TX deadheaded for a few ms but I don't know that you'd couple excess RF into the receiver doing that.  Maybe if you're on 80 or 40 you can afford to have the preamp off and even a bit of attenuation turned on for an extra measure of protection.  A bandaid fix for sure, I admit.  However, I have a K3 and if it senses excess RF into the receiver, it will start automatically taking such steps.

If your switch or relay had an extra pole, you could use it to ground the RX antenna input during transmit.  That still leaves you with that switching time vulnerability though.  The only thing I can think of for that is some kind of sequencer, like a microcontroller.  Or as others have said:

Something like the magic box would be the Cadillac solution, of course.

72-

Nick, WA5BDU


On 2/13/2013 10:06 AM, Jim, ND9M / VQ9JC wrote:
 

As a recent joiner of 4SQRP, I'm looking forward to getting back into building my own stuff. The NS-40 seems to be a popular and well designed rig, and my plan is to use my FT-857 for the RX side. Otherwise, the 857 is my day-to-day rig, and I have to protect it. (For QRP use, I drop the drive down and measure the output on an external wattmeter.)
 
So here's a newbie query from an old time ham (me!) who should know the answer but doesn't: What is everyone else who uses separate TX and RX units doing to mute their RXs when the TXs are doing their thing? A rule of thumb was given me a few days ago that there must be at least 40 dB attenuation to protect the RX front end, but that's also going to depend on what the TX power is to start with.
 
My old Hallicrafters RXs could handle a bit of a pop at QRP levels when I did manual switching. I'm a bit leery however about subjecting the "newfangled" 857 to similar treatment. I never had a Dow key which would've done nicely for the boat anchors, but - assuming I could put my hands on one - would a Dow key with its mechanical relay have fast enough response time to protect the 857's front end?
 
What other alternatives are currently in play?
 
Tks/73,
 
Jim, ND9M / VQ9JC





w5jhjerry <jerry@...>
 

Hi Jim,
Phil Salas, AD5X, wrote a QST article about a boat anchor T/R switch. He has a copy on his web site. It is here:
<http://www.ad5x.com/images/Articles/QSKBArevA.pdf>

One of the problems I see with his design is that he uses 2 relays. The first relay follows your keying or keyer. He uses this relay to mute the receiver and key the transmitter. A problem may occur because the relay will switch with the keyer and the relay will unmute the receiver before the transmitter signal has decayed. If you added a second relay to his design one which would be in parallel with the antenna relay, it would probably work fine. The additional relay would be used to mute the receiver. His design will handle up to 100 watts or so.
Jerry W5JH
"building something without experimenting is just solder practice"

--- In 4sqrp@..., "Jim, ND9M / VQ9JC" wrote:


As a recent joiner of 4SQRP, I'm looking forward to getting back into building my own stuff. The NS-40 seems to be a popular and well designed rig, and my plan is to use my FT-857 for the RX side. Otherwise, the 857 is my day-to-day rig, and I have to protect it. (For QRP use, I drop the drive down and measure the output on an external wattmeter.)

So here's a newbie query from an old time ham (me!) who should know the answer but doesn't: What is everyone else who uses separate TX and RX units doing to mute their RXs when the TXs are doing their thing? A rule of thumb was given me a few days ago that there must be at least 40 dB attenuation to protect the RX front end, but that's also going to depend on what the TX power is to start with.

My old Hallicrafters RXs could handle a bit of a pop at QRP levels when I did manual switching. I'm a bit leery however about subjecting the "newfangled" 857 to similar treatment. I never had a Dow key which would've done nicely for the boat anchors, but - assuming I could put my hands on one - would a Dow key with its mechanical relay have fast enough response time to protect the 857's front end?

What other alternatives are currently in play?

Tks/73,

Jim, ND9M / VQ9JC


Bill Cromwell
 

Hi,

I have come to prefer separate transmitter/receiver operation. I also
prefer to listen to my transmitter instead of having just a sidetone
audio oscillator (CW). In any case when I changeover from transmit to
receive the receiver antenna terminal(s) are directly grounded. Even if
I have a separate receive antenna that is still something I do.

My "pretty" receivers are setup to completely mute everything from the
antenna up to the audio stage and audio is left on for the sidetone. I
have used receivers that don't quite silence the rf/if stages and allow
us to set the level that can come though - *almost* silenced. The
receiver oscillator and mixer are running and the amplifiers are mostly
shut down. The transmitted signal becomes the "sidetone". I am modifying
my reveivers that don't work that so that they will. When we operate
that way we will notice anything that isn't just quite right including
"forgot to net the TX". Don't ask me how I know that (evil grin).

It's possible to do all of that with full break-in QSK or semi break-in.
I have come to prefer a manual switch that changes everything over for
the T/R functions. It is the easiest to implement and the most reliable.
I have a set of Kenwood Twins that are setup with the transceive cable
and semi break-in using the VOX. On that rig I just use the manual T/R
switch on the front panel of the transmitter..same as all the rest.
Sometimes the QSK process cuts off part or even all of the first dit and
if the first element is a dah it can become a dit. The manual switch
eliminates that. The first tap of the key is already live.

73,

Bill KU8H


Jim, ND9M / VQ9JC
 

Tks to everybody who replied both on and off list to my T/R Switching query. Overall, it looks like the Magic Box is the way to go. I can experiment and expand from there.
 
Forecast: Partly QRP with a chance of smoke!
 
73,
 
Jim, ND9M / VQ9JC
 
 

-----Original Message-----
From: Jim, ND9M / VQ9JC
To: 4sqrp <4sqrp@...>
Sent: Wed, Feb 13, 2013 4:06 pm
Subject: T/R Switching

As a recent joiner of 4SQRP, I'm looking forward to getting back into building my own stuff. The NS-40 seems to be a popular and well designed rig, and my plan is to use my FT-857 for the RX side. Otherwise, the 857 is my day-to-day rig, and I have to protect it. (For QRP use, I drop the drive down and measure the output on an external wattmeter.)
 
So here's a newbie query from an old time ham (me!) who should know the answer but doesn't: What is everyone else who uses separate TX and RX units doing to mute their RXs when the TXs are doing their thing? A rule of thumb was given me a few days ago that there must be at least 40 dB attenuation to protect the RX front end, but that's also going to depend on what the TX power is to start with.
 
My old Hallicrafters RXs could handle a bit of a pop at QRP levels when I did manual switching. I'm a bit leery however about subjecting the "newfangled" 857 to similar treatment. I never had a Dow key which would've done nicely for the boat anchors, but - assuming I could put my hands on one - would a Dow key with its mechanical relay have fast enough response time to protect the 857's front end?
 
What other alternatives are currently in play?
 
Tks/73,
 
Jim, ND9M / VQ9JC