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Tuesday, January 31, 2012

Some Audio Shielding

As I was aligning my "23/24 Re-cycle" 17 meter SSB rig, I noticed the tell-tale sounds of RF getting into my audio. (I guess I should be pleased -- my amplifiers are now producing enough RF to cause some trouble!) So this morning I went in and battened down the hatches in the AF part of the rig. Lead lengths were reduced. Unshielded cables were replaced with RG-174 (with due attention to "Murphy's Whiskers"). A ferrite bead was placed on the wire that carries voltage to the op-amp chip. I wrapped some foil (actually some of that conductive tape used to protect windows in alarm systems) around the plug on the D-104). And finally I cut out two pieces of PC board and made a shield for the whole AF section (see above). I think all this has had the desired effect. The audio sounds clean. I have the day off today, so if there are no Coronal Mass Ejections I hope to make some contacts on 17. Stay tuned!

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Monday, January 30, 2012

My .02 KW Linear Amplifier

Once again, die-hard QRP guys should probably look away at this point...

My Cycle 23/Cycle 24 refurbishing project continues. The JBOT amplifier in the 17 meter SSB rig is now working nicely, but unfortunately just as I got ready to make some contacts, the Coronal Mass Ejection hit us and conditions on 17 deteriorated badly. Looking for something to do, I noticed that in some pictures of my old Azores station, sitting alongside the SSB transmitter there was a small cabinet with a QRO/QRP switch on the front panel. Ah yes! My Ramsey Kit linear amplifier! This is a MOSFET-based device. Mine was designed for 20, but I changed the low pass filter and put it on 17. Later, in Italy, it went on 20 meters and for some reason I went back to the 20 meter low pass filter.

Yesterday I blew the dust off this thing, pulled out the 20 meter LP filter and replaced it with a filter that will let my 17 meter RF reach the antenna. Today I fired it up. Wow! 20 Watts! Look out 17 meters!

I really like the QRO/QRP switch -- it gives me the opportunity to lean back and say (just like the big guns) "Wait a second Old Man, let me turn on my LINEAR!" I even have a little fan in the box that you can hear when I go to the QRO position. Unfortunately it doesn't make the lights flicker. But we can dream...


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Sunday, January 29, 2012

Putting 17 Meter SSB Station On the Air

Magnificent, don't you think? The sun is rising over Northern Virginia, and 17 meters is starting to come alive. Yesterday I finished the tweaking and peaking of the JBOT amplifier for the transmitter. It is nice and stable now. (And yes, Steve, it has a low-pass filter!) On top of the transmitter cabinet is the receiver. It is a Barebones Superhet designed by Doug DeMaw and built on a FAR circuit board by Dale Parfitt, W4OP. I changed it to 17 meters and broadened the filter response for use on SSB. Both the transmitter and the receiver use variable crystal oscillators, with two crystals in each (switch-able from the front panels). The frequency coverage of of the transmitter and the receiver match up fairly well (good thing!). Wish me luck! Today I will venture forth amidst the coronal mass ejections and try to make a few SSB contacts on good-ol' 17.

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Saturday, January 28, 2012

A Good Deal on SolderSmoke -- The Book 30% off!

Thirty percent off from Lulu! That's pretty good! Offer ends on January 31.
See "SolderSmoke -- Global Adventures in Wireless Electronics" at:
http://soldersmoke.com/book.htm

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Friday, January 27, 2012

Some Amazing German Knack


Michael, DL4MGM, sends us this report from a country in which "the knack" has deep linguistic and cultural roots. Wow, that's my kind of hamfest! Test stations for homebrew gear. And the key-powered transmitter is a great idea. I know there is a lot of energy going into those straight keys -- as a kid, my arm would hurt after an afternoon of unanswered CQs. Thanks Michael!

Hi Bill,
I do not know how big your german listener base is but in any case I want to draw your attention to the "Amateurfunk Tagung München" on 10th and 11th of March 2012. It is a german amateur radio convention which takes place every other year at the University of applied sciences in Munich. There is one speaker track with, mostly german, talks on a wide spectrum of topics related to our hobby. The organisers did a particularly good job in getting Joe Taylor, K1JT, as a speaker to talk on "Recent Advances in Amateur Weak Signal Communication" (10. at 17:00 local time). Needless to say that I'm looking forward to this.
Apart from the talks there will be booths and exhibits from various groups and also some well known commercial sources of RF/microwave components, modules and the like.

Another highlight are the lab places, including personnel, where you can have your home brewed stuff tested up into the high double digit GHz range. I always take home new ideas from just strolling around there and looking at the things people bring for testing...


The last thing I want to mention is the current "operating and construction challenge" because it so right up our alley. It is something like an "Energy harvesting transmitter key". The task is to build a 2m, 80m or 10m transmitter which is completely powered by the energy put into the key movement. In order not to stifle inovations, a lot of liberties are granted such as keying by foot. It will be allowed to pre-charge the energy storage component by keying up to to 10 "v"s with the transmitter turned off. As proof of operation, a 160 character random text message will have to be send to an adjoining room. Ranking criteria (in descending order) will be:
- Peak transmitter power during transmission of the last character. - Construction and handling - Message errors - Keying speed / total transfer time - Tone quality and frequency stability Sounds like it will be a lot of fun... Here the link to the german site: http://www.darc.de/distrikte/c/amateurfunktagung-muenchen/

That's all for now.
Keep going!

Kind regards from southern Germany de
Michael, DL4MGM




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Wednesday, January 25, 2012

Toroidal Travails II

Steve Smith sent me a good article on broadband transformers. Reading through it, it occurred to me that perhaps using a heavier gauge wire in that PA output transformer might help. So I rebuilt the FT-50-43 transformer and put it in the final. No joy -- output was still down around 1 watt. Then I tried adding two turns to the secondary (on his web page Farhan advises experimenting with the turns ratio in an effort to improve output). Again, no joy. So I went back to the FT-37-43 transformer with 12 turns on the secondary. This yields the best results so far: about 2.5 watts. Still a bit low, but for some reason, the smaller cores seem to do better. Toroidal transformer tweaking to continue... Stay tuned.

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Tuesday, January 24, 2012

Toroidal Transformers: Does Size Matter?

I continue to tweak and peak the JBOT amplifier in the Azores 17 SSB transmitter. On this version I used some FT-50-43 toroidal cores instead of the smaller FT-37-43 cores recommended by Farhan. This morning I was experimenting with the output transformer. I seem to get noticeably more output with a transformer made with four FT-37-43 cores than I do with one made with four larger FT-50-43 cores.

I noticed something similar on my previous JBOT: performance improved when I switched from some relatively large binocular cores and went to the recommended FT-37-43.

So, what do you guys think? Could there be lower losses using the smaller cores? Any other reason why the smaller transformers seem to be doing better?

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