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Sunday, October 13, 2019

More on the ET-2 : Better Pictures and More Circuit Description. Some Thoughts on Simplicity


So yesterday I made my first contact using my ET-2 rig.   Last night I got an e-mail from Gary, the fellow at the other end of that contact: 


Evening Bill, N2CQR….Yes I did learn about you from the spot on the DX Summit cluster. I tuned to the freq to see if I could even hear your 80 mW and you were a good real 569 when calling CQ.  You built up to a real 589 on the later transmissions. I did not have either of the two pre-amp positions on in the ICOM 756 Pro II. There was not any QRM on the freq either. Your spot indicating the 80 mW is what really got my attention.

My antenna is a 2 element yagi at about 115 ft and it really works great for me.

Thanks for the picture of the great little transmitter. Glad to be your first DX QSO with it. Hi Hi  Maybe again soon.  My pleasure to work you.
73, Gary, K4MQG
Fort Mill, SC

Farhan commented on yesterday's post, saying that it was hard to tell (from my pictures) where he rig started and ended.  He was right.  So this morning I have tried to clean up my bench a bit -- I hope these pictures are better.  

Above you see the whole rig.  The transmitter board is right next to the key that Farhan gave me.  You can see the 7040 crystal.  A C-Clamp holds to the bench the piece of scrap plywood that serves as the base for this rig.  Next to the C-Clamp you see the TR switch -- the just switches the antenna -- both transmitter and receiver are powered at all times.  I can hear the transmit signal in the headphones and this serves as my sidetone. 

Here is a close-up of the transmitter with the schematic below: 



The transmitter is VERY simple.  Nine parts, including the low-pass filter.  You can barely see the J310 FET to the right of the crystal. 

Here is the receiver:


I really like N0WVA's regen.  The green diode in the source circuit is the key.  This one does not squeal when you go into excessive regeneration (when you think about it, regens should NOT squeal at audio frequencies -- but most do).  Also, the green diode dims a bit when you are at the right amount of regeneration.  In the picture you can look down the tube of the variometer that Pericles HI8P gave me many years ago.  The big variable cap is from the junk box -- I think it may be from a Johnson Viking transmitter.  Note the long shaft with the insulating connector -- this is to reduce the hand capacity effect.  On the right you see a smaller cap with just one vane -- this is my fine tuning control --- with the smaller cap at mid range, I would just set the big capacitor to put the receiver at 7040 -- with the smaller cap I could tune +/- 12 kc.  I also used an insulating shaft on the smaller cap -- the connector for this one is from an old 1930s era regen that I picked up at the Kempton Part rally in London.

Instead of the audio transformer and Radio Shack headphones, I just used some old DLR-1 WWII Headphones.   They are very sensitive and work well. 

Lots of soul in this new machine:  The variometer from Pericles.   The WWII headphones.  The 1930s era shaft connector.  The circuit idea from the Autumn 2001 SPRAT.  Farhan's key. 

I recently read on Hack-a-Day of a new FPGA chip that has on it 35 BILLION transistors. I'm sure that thing can produce some fascinating results, but can anyone really understand it, or feel that they really BUILT something that has that kind of chip at its center?   On the other hand, I did rely on a lot of modern digi technology in this project:  The Reverse Beacon Network reported back that my unanswered CQs were in fact getting out (one as far as Kansas to K9PA).  And in the end I had to ask -- via the DX Summit Spotting cluster -- for someone to listen for me.   So I can't go full Luddite here.  And I wouldn't want to have to use a rig this simple every day.  No way.  It is just too hard to use. But there is a beauty and a challenge in simplicity.  There is some virtue in using just two transistors instead of 35 billion. 

Thanks to N0WVA, W2UW,  VU2ESE, HI8P, K4MQG, The G-QRP club and their inspirational journal SPRAT, the RBN and the DX Summit. 

7 comments:

  1. In the thirties, electronics was big and expensive, and many hobbyists had little or no money.

    So it's understandable that things were primitive. Not just regen receivers, but buikt on breadboards and relatively few bypass capacitors etc. There were transceivers at some point, usually for "UHF" where a single tube was a superregen on receive and a modulated oscillator on transmit. Such things were ground-breaking at the time, allowing a push to higher frequencies without expensive equipment. Frank Jones supergainer fit this too, a way to get a superhet without cost or complication.

    But other than novelty, what's the point now? Switching a transistor like that is going to affect performance, just like all those VFOs that had a switch to change coils for another band. Transistors are cheap, and tiny, adding one will barely be noticed, but may allow for simpler wiring or design. Maybe bilateral IF strips can be simplified by a few extra transistors and parts and seperate transmit and receive IF strips. Wes Hayward event went all the way once, duplicating the crystal filter in both sections (though likely they didn't cost him, whike most others would have to think twice). Using a device for each oscillator and switching B+ can make more sense than switching coils or crystals.

    Decades ago Ray Moore made the point in a Ham Radio article about a fancy receiver that hams coukd afford an extra stage to get gain rather than squeeze it out of one stage (complete with neutrilization) or add shielding and more bypass capacitors to simplify other things. That contrasted with commercial equipment where design cost could be spread over every unit, but an extra device or more bypass capacitors would add cost to every one of the end products.

    In the thirties, our hobby world woukd have been seen as science fiction, but we live in a world where parts are cheap.

    Michael

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  2. Great work Bill! Please keep the projects coming.

    Hi Michael, parts are cheap these days but this isn't about the money.

    Sometimes it's nice to do a lot with little - especially if you tweaked that design into working as well as it could and/or made it with a nod to the ancients.

    I've had far more fun with extremely simple stuff I was (almost) surprised to make a contact using than more complicated endeavors that I'd expected to make contacts with.

    And ultimately it's a personal and a "per-project" choice. The next project could use 6 dB more parts and deliver 3 dB more satisfaction :)

    73, Andrew
    G6ALB

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    Replies
    1. I realize this is about simplicity as a challenge, but the same effect could be had by using a second FET rather than tgat multipole switch. It's still a regen receiver with an FET transmitter, but it gets around that switch.

      The switch complicates things, and makes the wiring harder, and if bought most likely is more expensive than the extra FET.

      Design often means that "complicating" something actually makes other things simpler.

      If I didn't understand the goal I might have said "why not buikd a better receiver or a multistage transmitter". Instead, I merely dismissed the use of an FET switched between receive and transmit, which doesn't simplify but does seem done merely for the novelty factor.

      Michael

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  3. In fact, I arrived at the same conclusion that Michael did regarding the switch. It did complicate things. It made it hard for me to get the regen to work properly. So I did go with two FETs. And I suppose it depends on how you look at it -- I AM using only one FET on transmit, and one FET on receive. Just not the same one!

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  4. When I was about 11 I thought it would be neat to have an ecternal microphone on my 100mW walkie talkie. I might have been able to do that, but I couldn't figure out how to add PTT. No fun if I had to use the switch on tye walkie talkie. But tye switch was multi-pole, and at that time I couldn't figure it out, let alone remote it.

    It of course used the transistor on transmit and receive, and the switch needed to make it posdible. The manufacturer thought it was cheaper to reuse the bipolar transistor.

    Michael

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  5. Glad to see you have the rig on the air. What a fun project. I never got around to pairing my receiver with a transmitter. I had plans for a one transistor transmitter with about a watt out and VXO control. Two transistors can make a decent station, its just that most havent built a really good regen. When done right, even one transistor can make a practical receiver as you have done.

    N0WVA

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  6. Probably the most incredible variamoter's I've seen were from a single page at the G3YMH site. Its been years since I had seen it and almost gave up finding, luckily, I had used google bookmarks and here it is ! http://www.g3ynh.info/comps/Vari_L.html

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