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Friday, May 17, 2024

Band Imaging Rigs (Receivers and Transceivers) -- Video from WA7MLH

In the video above (from 16 years ago) we see Jeff Damm, WA7MLH's  band-imaging receiver for 75 and 40 using an IF of 1.750 MHz and a VFO of 5.2 - 5.7 MHz,  For a signal at say 3.579 MHz (!) you subtract the signal from the VFO and you end up at the IF.  For a signal at say 7.030 MHz you subtract the VFO frequency from incoming signal and get to the IF.  (By the Hallas rule you get sideband inversion on 75/80 meters, but Jeff was on CW so this doesn't really matter.)  

Sixteen years ago this receiver was a work in progress and Jeff was having some trouble with the bandpass filters. I had similar trouble with bandpass filters. Like Jeff, I eventually got this sorted.  

I was happy to see a comment from my friend Joanthan-san on Jeff's old video.  

Jeff has an awesome and rececntly updated QRZ site:  https://www.qrz.com/db/wa7mlh

Band imaging like this is an old idea, and a very good one:  I used a slightly different scheme:   Start out planning on using a single conversion design.  Pick two bands you are interested in.  Select an IF midway between the two.  Build a single VFO that --when added to the incoming (or the outgoing) signal will get you to one of the bands, and when subtracted from the signal will get you to the other one.  Bob is then your uncle.  Two bands, with minimal switching. 

I got started with band switching with my Mythbuster rig:  I would get 75 and 20 meters.  The IF was midway between the two at 5.2 MHz.   My VFO (from an old Yaesu FT-101) ran around 9 MHz.  Boom, it worked, with the added benefit of receiving and transmitting LSB on 75 and USB on 20 with no switching of the BFO/Carrier Oscillator.

Then I did 17 and 12 meters.  Kind of a WARC-band special.  IF was at 21.4 Mhz.  VFO ran around 3.5 MHz.  So by adding the incoming modulated signal 18 MHz signal and the VFO, you get to 17 meters.   By subtracting the VFO from the incoming 24.9 MHz signal you get to 12 meters.  And both are on USB (apply the Hallas rule), so again, no switching of BFO/Carrier frequencies are required. 

Finally,  at solar max, I built rigs for 15 and 10.  Here the IF was 25 MHz.  Again the VFO was around 3.5 MHz.  Adding the incoming 21 Mhz signal to the VFO gets you to 25 MHz, subtraction of the VFO frequency from the in coming 28 MHz signal takes you to 25 Mhz and thus 10 meters.  Again, no sideband inversion (Hallas rule).   Both signals are USB and stay on USB. (I built two versions of this rig -- one stays in Virginia, the other is heading to the Dominican Republic.) 

In the ARRL book QRP Classics, there is an article from the 1990 Handbook entitled "A Band-Imaging CW Receiver for 10 and 18 MHz."  The article may have been based on a receiver built by Dave Newkirk AK7M (Rod Newkirk's son). Unfortunately in the write-up for the ARRL handbook, the drafters repeat the oft-repeated myth about how 9 MHz IF and a 5.2 MHz VFO would supposedly produce LSB on 75 and USB on 20.  This just doesn't work.   But if you put the IF at 5.2 MHz and the VFO at 9 MHz, it does work, as demonstrated by my Mythbuster rig. 


  1. Glad to see someone besides myself who is all homebrew and does not own any commercial ham radios (even W7ZOI has an IC-7300 per his QRZ page), and I wonder if there are any others?

  2. Me too Walter. The only commercial rigs I have are old boatanchors.

  3. that looks like a BC-221 repurposed.

  4. All HB here. 100%, including Power Supplies, RF Power Meter, LF-6GHz Synthesized Sig Gen, LF-3GHz Spec Ann, Freq Ctr, 2M FM Xcvr and ATU plus Antennas. Commercial gear went to Scout Camp long ago. It looked too "good".

  5. I am sorry but I feel that is an unnecessary implication about W7ZOI who in my opinion is the greatest homebrewer of all time. If someone chooses to have commercial and homebrew equipment that is their preference. Other people may want to have only homebrew gear. This is okay too.
    Amateur radio is dying a slow death and we need to embrace differences and come together, not get too judgey about what others are doing or think we are better because we prefer one thing over another.

    1. Sure. To each his own. This is a hobby and it is all for fun. But I have always found it to be an admirable thing when someone has homebrewed their station. And the more homebrew it is, the more admirable it is, in my view. I remember the first time I saw a picture of Frank Harris K0IYE's station in World Radio magazine. For me, THAT was an admirable station, certainly more admirable than one resulting from the swiping of a credit card. Heck, that is how I got my Iphone -- and I don't consider it admirable that I have an Iphone in my pocket. This blog is about homebrew radio, so it should come as no surprise that people here find HOMEBREWING RADIOS to be an admirable thing. Here are some blog links to Frank Harris's book and to his admirably HOMEBREW station: https://soldersmoke.blogspot.com/search?q=K0IYE
      73 Bill N2CQR

  6. W7ZOI is the G.O.A.T of Homebrew, no question!


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