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Don Dulmage
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VE3LYX Ham Since 1980

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Other Callsigns
First issued VE3LYU

My Ham Radio Interests
Homebrew tubes CW and AM. Minimalist style.
Skeds for low power QSOs with homebrew stuff.

50C6 Cw rockbound with matching 12sn7 regen.
01 TNT 40M with matching 01 regen
40M hartley CW
80M x 40M Am transceiver HB
Two No 19 Wireless Sets
6l6 Breadboard Cw TX and matching 6sl7 regen.
BC454 recvr Operational 80M
ARC 5 T18 transmitter which now covers all of 80M band in CW and AM (cathode modulated through CW key jack)
Twin 811A HB linear Amp.

Other Interests
Speak Deutsch at a functional level, can get by in French but it is hardwork for me.
Make fiddles and play them. (gospel and country)
Drag racer . I run The Senior Dragster. Slant six powered.
I race it at Picton Airfield
Am a writer. I have two books published and many magazine articles in both the USA and Canada. I used to have my own opinion column in a local paper for several years.(View from the Ridge)
Cast aluminum for fun.
Also raised cattle for several years and trucked them. I also bought and sold for others. (Dolmetsch Beef Farm)

In the interest of allowing others to enjoy their clubs I now refrain from joining.(does not play well with others)

Loop Modulation from WWI days


2/13/2014 3:09:31 PM (0 comments) Add a commentAdd Comment

Near the end of WWI there were some experiments made with putting voice on transmitters apparently for aircraft use. There is little to be found on it but recently a friend Lou VE3AWA found and restored a transmitter that had a form of it. It had a jack in the front panel labeled Microphone connected simply to a large loop of copper wire running around the main tuning coil. When he shared that story on the AWA Yahoo group it rang my bell since I had read of a similar method being used to control a regen's regeneration. Different application but exactly the same principle. So I grabbed my old 45 tube TNT and gave it a try. By the end of the day I had achieved decent modulation. Within a couple of weeks I had used it for a QSO on 40M and have several times since. I spent some time making the TNT more stable as it was really just a curiosity that saw an antenna only once or twice a year.
By moving the variable cap deeper into the chassis and installing a vernier drive and a BIG control knob I was able to cure most of its bad habits. It is a much better radio now. The longest QSO has been a distance of 369 miles ATCF. It is really interesting to explore forgotten technology from 1918 or 1919 and discover it works so well. Why was it never popular? My guess is it was the right idea presented to the wrong person and was soon forgotten. I met one other ham who has used it and Lou found an article from the very early 20s where ARRL lab tested it and on air tested it, with good reports and success. Oh, it is not broadcast quality audio or anything and the whole AM world will not be changing nor are the vast majority interested. However for me I am fascinated at how radio operators must have felt back in the late teens of the previous century experimenting with such interesting technology.
I am contemplating a Loop Mod Net on 40M AM if we get a few more rigs up and running. For those with such rigs and those interested in it. The signal is quite narrow or appears to be. As one of my contacts said after our QSO. "It ain't the best audio I have heard but it sure was fun!" Signal quality is already improved to the point I am recognizable by my voice. There is a lot of exploring yet to do. Biggest obstacle for most? It is too simple.
Did further work today on another transceiver I had designed and built which is basically a Hartley mopa.
It now has a real good working loop modulation system and I am anxious to use it for an on air Qso.
I have now installed the system on 5 transmitters here in my shack. I have become quite comfortable with it and how to make it work properly.
Worked most of the day on the little transceiver. spent more time in the tank circuit and reworked some of it.. I now have the power way up from where it was. In fact it is pinning the FS meter and before it was about 1/6th scale at full power. I need a sig report and it will come soon I hope. Not totally happy with the rig yet but surprised at the power level. I always am. Every time I make improvements in the tank circuit I get seemingly huge power gains for relatively minor corrections. Makes me wonder how many others are working with seemingly slight mismatches and wasting unknowingly huge power %wise. I am going to keep working on this little rig. It is already doing more then I thought it could.

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