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Thursday, February 23, 2017

Walter KA4KXX's "Al Fresco" Oz DSB rig with VFO Mod


A while back we ran a post about the MDT 40 DSB rig out of Australia. Walter KA4KXX liked the design so much that he built his own version and, with it, made his first homebrew phone contacts. I always say that DSB is a great way to break into the world of microphones.  Walter is obviously on the right path -- not only did he come up with a nice Al Fresco DSB rig, but he modified the VFO to get additional coverage and to incorporate a frequency counter.  FB Walter!

Walter KA4KXX writes:

Since I earned my Ham Radio license in about 1979, I have always operated only on CW since I like to build all my own equipment, but recently at the SolderSmoke website I discovered the MDT 40 Meter DSB Transceiver, and decided this was the design I had always been looking for to finally build and operate on phone.

After I made my first phone contact after only 5 minutes of trying, just a few weeks ago, I was so excited I sent an email thanking designer Leon of ozqrp.com.

Then I modified the VFO further to cover the entire 40 meter USA General Class License phone band, which is 7.175 – 7.300, in two overlapping steps.  I also added a 5K fine frequency adjustment, used a more friendly 1SV149 Varactor diode which I purchased on EBay at very low cost, and also added a high impedance buffer (found at the website listed below) to the VFO to drive a frequency counter.
 
http://www.arising.com.au/people/Holland/Ralph/buffer/highimpedanceprobe.htm


I was able to implement these modifications very easily since I always make my own un-crowded state-by-stage Manhattan style circuit boards and build first on a breadboard.
So far I am very pleased with the results.


Walter KA4KXX

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