Date
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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
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Rich Fowler <k8meg@...>
--- On Wed, 2/13/13, Jim, ND9M / VQ9JC wrote:
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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
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Wayne Dillon
Hi Jim,
toggle quoted messageShow quoted text
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:
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http://www.qsl.net/kc0pmh/ Under construction but please visit anyway.
QRP - EFFICIENCY AND SKILL, NOT POWER.
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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:
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Jim,
toggle quoted messageShow quoted text
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:
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w5jhjerry <jerry@...>
Hi Jim,
toggle quoted messageShow quoted text
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@yahoogroups.com, "Jim, ND9M / VQ9JC" wrote:
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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
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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
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