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Monday, February 23, 2015

Parasitic Anguish on 40 then... Homebrew Transceiver Heard by Homebrew Receiver (with a PTO!)



Oh man, I was struggling yesterday. I guess I had been lulled into a false sense of security by the phenomenal ease with which I had put my BITX 17 on the air, then added a 120 watt amplifier, all without any sign of the dreaded feedback and parasitic oscillations that had plagued almost all of my previous projects.  So when I decided to add the low pass filter and the switching/relay arrangements needed to use the amplifier with my BITX 20/40 rig, I kind of expected a similar trouble-free experience.   

WRONG!  And you know what?  I think guys on 40 and 20 are a bit less forgiving and collegial than the folks on 17. As I struggled to exorcise the transceiver, I'd make some changes then hopefully go out onto the airwaves and call CQ, looking for a signal report.  Well, I got them.  Many were not accompanied by call signs.  I'd be in contact with someone who was trying to help, and -- as we were trying to figure out what it might be -- we'd be bombarded with harsh, sometimes angry, anonymous commentary: "YOU'RE 20 kcs WIDE!"  "Are you on AM?"  "You have a CARRIER!"  One fellow scornfully told me "That little QRP rig of yours is not ready for prime time."  Ouch.  (I didn't realize we were on prime time.  Isn't this AMATEUR radio?) 

Others would answer my CQ by announcing that I was "on the wrong frequency."  Others would respond (off frequency) and tell  me I was distorted -- I'd ask them to tune me in, then they would say, "Oh yea, you are OK -- you were just on the wrong frequency." Some of these guys seemed to be under the impression that there are "channels" on 40 meters.   It was a real disheartening mess.

Then came the saving grace.   I got the e-mails that appear below.  WOW! My faith in ham radio was renewed!  In the 18 months that I've been running the BITX rigs, I've never once worked another station using a homebrew rig.  But Rick and I were 3/4 of the way there yesterday.  And he was using a direct conversion receiver of his own design, with a PTO in an enclosure made from "flattened out tin-plated food tins."  Fantastic!  It was as if the radio gods had arranged all this to pull me out of the depths of parasitic despair!  Thanks Rick!    A video of his receiver picking up my BITX 20/40 appears above. 

Pete and I will talk about the actual troubleshooting in the next podcast.  I am HOPING to have it fixed by then.  I may have to sacrifice some chickens to Papa Legba." 

................

Bill,

I'm a long-time SolderSmoke podcast listener, and today one of my ham radio dreams came true.

I was listening to 40 meters today on my homebrew direct conversion receiver, and I heard your call.  At first I didn't believe it was you, but  there you were. 

At first I just sat there dumbfounded, just listening, but soon realized that I should make a video of this "rare DX" (rare DX for me hi hi), and post it on YouTube for you to review.

My apologies for the low audio in the video.  I was using my iPhone and its inboard mic leaves a lot to be desired, but the best audio of you is at 0:13, 0:50, and again at 2:12 into the video.

Heard you on 7.16 MHz, Sunday 2-22-2015 at 10:15 a.m. local east-coast time (15:15 UTC).

I'm located in Manchester Maryland (North - Central Maryland).  My homebrew 40 meter rig is a PTO tuned direct conversion receiver with all discrete components.  My antenna is a simple wire dipole about 6 feet above the ground just outside by workroom window.

Below are links to the YouTube video of your QSO , and the schematic the DSB transceiver that you were received on.  The rig is one that I designed, based on the published works of many home-brewers from the web.  I call it the Lakeside 40 (in homage to Peter Parker's Beach 40 transceiver).

So far I only completed the receiver section, and hope to complete the transmitter sometime this summer so I can use the rig at Lake Marburg (at Codorus State Park in PA), thus the "Lakeside" in the rig's name.

http://youtu.be/emsKg5n5-0c


http://www.remmepark.com/circuit6040/lakeside40.gif


73
Rick - N3FJZ



Bill,

Yes, what a coincidence with the PTO! That's the same WA6OTP PTO design
I based my PTO on.

I created a webpage tonight(very much a work in progress) so you can see
the details of how I constructed my PTO in the Lakeside 40, as well as
my rendition of a BITX 20. Click the [Permeability Tuned Oscillator], or
[My rendition of a Bitx 20] links on the left of the page.

The webpage is here:
[http://www.remmepark.com/circuit6040/index.html]

The ground plane for the Manhattan construction (and RF tight enclosure
for the PTO) are made from flattened out tin plated food cans, and the
coil-form for the PTO is cut from Masonite wall panel material with my
scroll saw.

Don't get discouraged from the less than enthusiastic response from the
others about your signal, pay them no mind; I'm sure they simply didn't
realize the significance of what it represented.  To me, your signal was
the most perfect signal I have ever heard.  It was perfect because I
know (from your pod-casts, and my attempts at homebrew) what it took for
it to be produced.  Its existence, and the fact that I successfully
received it on my little homebrew rig too, represents the fundamental
core foundation of Amateur radio; experimentation, building equipment
with your own hands from scratch, expanding ones knowledge in the radio
art, and most important, having fun and enjoying the excitement that
comes from using gear that *you* built.

I cannot put into words how significant hearing your signal was for me
today - thank you!  My biggest regret is that I didn't have a means of
transmitting yet on 40 meters, and my Bitx 20 is not ready yet, 

perhaps in the future we can have homebrew to homebrew QSO's
where we can fine-tune our designs and tweak things (however we'll have
go above 7.175 MHz, or 14.225 MHz since I only hold a General ticket at
the moment).

Rick
N3FJZ.


PTO another view.

Rick's PTO


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3 comments:

  1. Hi Bill,

    The Italians have an interesting way of looking at those who deride you while you are trying to get some input on what may be the problem. WE DON'T GET MAD, WE GET EVEN!"

    Your Italian friend Pete N6QW

    ReplyDelete
  2. I think you have just run headlong into the difference between homebrewers and appliance operators. It is sad that the hams you contacted had so little appreciation of what it takes to build a radio and work out the bugs. I would be psyched to be able to assist in troubleshooting your new rig, as I am sure most of your readers and listeners would be. It reminds me of those qro ops who get insensed by a qrp signal. Ham radio has a history and tradition of homebrewing. It is disappointing when you run into folks on the air with so little tolerance or curiosity. You can't let it get you down! Their view is myopic. You can't let the ignorant tarnish your passion.

    -Jeff
    KF7RPI

    ReplyDelete
  3. Brilliant stuff, I enjoyed reading this so much. This is the epitome of Amateur radio, hearing and/or working people on something you made.

    Never let the "knockers" put you off, it's a broad hobby and there are plenty of decent people who will work with you to iron those bugs out and give you great contacts.

    More power to your collective elbows!

    VY73,

    Andrew
    G6ALB
    M0BXT

    ReplyDelete

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