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Author Topic: QSK T/R Switch for Boat-Anchors  (Read 25326 times)
AD5X
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Posts: 1622




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« on: August 03, 2010, 04:49:30 AM »

I just added a boat-anchor QSK T/R switch article in the "Articles" section of my website at www.ad5x.com.  Not difficult to build, and it works great.

Phil - AD5X
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N3QE
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Posts: 5576




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« Reply #1 on: August 03, 2010, 05:28:13 AM »

I agree fully that separate transmitter and receiver is the "way to go" for QSK. Way better than any modern transceiver IMHO. Although the Elecraft K2 QSK and Ten-Tec QSK are pretty decent for transceivers - they are still transceivers and cannot reach the glory of separate T and R.

But if you've only ever used relay-switched QSK, you truly are missing out on the joys of electronic T/R switching. Any of the 50's or 60's ARRL handbooks has at least one fully electronic T/R switch construction example and they really do work seamlessly. When set up it "feels like" you can still receive even with your key down, that's how seamless it can be. Truly a joy.
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AD5X
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Posts: 1622




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« Reply #2 on: August 03, 2010, 09:53:42 AM »

Yep - I agree that fully electronic T/R switching is great.  I built a vacuum tube T/R switch from a Handbook back in the '60s when I was a kid.  Worked great.  But it is hard to beat today's high-speed signal relays if you want a simple QSK switch.  The relays are fast, reliable and surprisingly quiet.  And they make for an essentially lossless switch that is very forgiving of any mismatch conditions.

Phil - AD5X
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AA5WG
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Posts: 511




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« Reply #3 on: August 16, 2010, 02:11:25 PM »

Hi Phil:
Neat article.  Is your system "true" QSK or is it conventional TR switching?

I am looking for a way to add "True" QSK to my Drake C-Line.  I also would like add "True" QSK to a Hammarlund receiver and Drake T-4XC or a Hammarlund receiver to Hammarlund transmitter combination.  I like Boat-Anchors.
73,
Chuck - AA5WG
aa5wg@yahoo.com
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KE4JOY
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Posts: 1418




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« Reply #4 on: August 16, 2010, 03:20:52 PM »

Im definatly going to have a look at this article maybe get the old SB303 workin again !
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AD5X
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Posts: 1622




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« Reply #5 on: August 17, 2010, 04:43:02 AM »

"Is your system "true" QSK or is it conventional TR switching?"

It is true QSK - i.e. you can hear receive signals between your dits and dahs.  This does use relays - not PIN diodes.  So you can hear the relays operating if you aren't wearing headphones.  But the relay clicking is not loud.  The only delay is the drop-out delay of about 8ms, which gives time for the RF output to decay to zero before the switch occurs when unkeying - so there is no hot-switching of the transmittter output.  The gap between dits and dahs is 1200/WPM in milliseconds, so theoretically you'd have to be operating at 120WPM before you couldn't hear anything between your dits and dahs.  You can shorten the drop-out delay by changing the 0.47uf capacitor to a smaller value.  O.33uf would give about 6ms drop out delay, and 0.22 would give about 4ms drop-out delay - but be carefull you don't go to far.  Normally you'll start causing key-clicks when hot-switching on un-key.  I've found that 8-10ms drop-out delay works fine and leaves plenty of time for hearing receive signals between the Morse elements.  Anyway, it works great.  I'm having a ball with my Ranger/2B station now!

Phil - AD5X
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AA5WG
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Posts: 511




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« Reply #6 on: August 17, 2010, 05:18:19 AM »

Phil:  Thank you for your information.  Are you going to offer a board and kit for this QSK modification? 
73,
Chuck - AA5WG
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AD5X
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Posts: 1622




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« Reply #7 on: August 17, 2010, 05:39:10 AM »

I hadn't planned on laying out a pc board for this.  It is pretty easy to wire up on the perf-board.

Incidentally, your ability to hear between Morse characters will probably be more a function of your receiver's AGC speed.  Make sure it is on FAST AGC.  As an example, Drake made a modification to the 2B to improve its AGC action for QSK operation.

Phil - AD5X
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AA5WG
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Posts: 511




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« Reply #8 on: August 17, 2010, 07:58:15 AM »

Hi Phil:
Do you know of a good pc board layout software program?  I prefere to have your nice work on a pc board.
73,
Chuck - AA5WG
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AD5X
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Posts: 1622




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« Reply #9 on: August 17, 2010, 09:43:48 AM »

I use expresspcb (www.expresspcb.com) for my prototype pc boards.  They have free schematic and layout software.  Three prototype pc boards (2-layer with plated-thru holes) cost around $60.

Phil - AD5X
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AA5WG
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Posts: 511




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« Reply #10 on: August 17, 2010, 02:27:05 PM »

Phil:
Thank you for the tip on expresspcb.  I will go back to web site and look up the schematic and component details.  I have another question but I have to look up some data first.  Thank you again.
73,
Chuck
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W3RJ
Member

Posts: 7




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« Reply #11 on: October 14, 2010, 07:46:01 PM »

Everything you need to know about true QSK.  The use of an electronic T/R switch severely degrades the performance of a decent receiver.  The implementation could easily be modernized.

R. Klinman, "A Vacuum Relay TTL QSK Antenna Switch", CQ Vol. 32 No. 7 (1976).

R. Klinman, "Vacuum Relay QSK in a Commercially Equipped Station. Part 1:
The Collins S-Line", CQ Vol. 33 No. 12 (1977).

R. Klinman, "Incorporation of the Vacuum Relay QSK into a Commercially
Equipped Station, Part 2: The Heath SB400/401", CQ Vol. 34 No. 7 (1978).

R. Klinman, "Drive Equalization and Isolation Amplifier - Collins S-Line
VFO Injection", CQ Vol. 35 No. 4 (1979).

R. Klinman, "CW Transceive with Full Break-in for the Collins S-Line",
CQ Vol. 36 No. 9 (1980).

R. Klinman, "Full Break-in with the Drake T4XC-R4C Using the Vacuum Relay
QSK", CQ Vol. 36 No. 3 (1980).

R. Klinman, "Note on the Use of the Vacuum Relay QSK with SSB-VOX
Operation", CQ Vol. 36 No. 11 (1980).

R. Klinman, "Improved Spot Capability for the T4XC and R4C", CQ Vo. 37
No. 9 (1981).

73 Rich W3RJ


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N2EY
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Posts: 5067




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« Reply #12 on: October 15, 2010, 03:16:38 AM »

  The use of an electronic T/R switch severely degrades the performance of a decent receiver. 

I think that depends on the receiver, the TR switch, the band and the overall setup. For example, if the noise figure of the TR switch is higher than that of the receiver, degradation of sensitivity will result. Or if the IMD performance of the TR switch is worse.

quote author=W3RJ link=topic=69975.msg475572#msg475572 date=1287110761]
The implementation could easily be modernized.
[/quote]

No argument there! Besides the articles you mentioned, consider this one, which doesn't use a vacuum relay:

"A Complete Break-In Unit for CW" by Robert McGraw, W2LYH, QST Jan 1960 (Pg. 20)

The transmitter is left connected to the antenna all the time, and the final is biased to cutoff when the key is up. A small high-speed relay disconnects the receiver and keys the transmitter when the key is down.

Check out W2LYH's other articles for some really beautiful examples of homebrew.

73 de Jim, N2EY
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AA5WG
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Posts: 511




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« Reply #13 on: October 27, 2010, 04:15:55 AM »

Any more ideas?
Chuck
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KE4JOY
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Posts: 1418




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« Reply #14 on: October 27, 2010, 07:36:28 AM »

Is there any way this could be modified to also work with phone modes?

I know the toggle switch T1 could be used manually but it would be handy to have it automatically key over with the ptt for split operations.
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