{"id":4312,"date":"2018-02-19T12:17:00","date_gmt":"2018-02-19T01:17:00","guid":{"rendered":"https:\/\/www.homebrewradio.us\/blog\/2018\/02\/19\/a-wonderful-troubleshooting-story-thailand-mixers-a-simpson-260-microwaves-and-some-black-tape\/"},"modified":"2025-07-21T16:55:14","modified_gmt":"2025-07-21T06:55:14","slug":"a-wonderful-troubleshooting-story-thailand-mixers-a-simpson-260-microwaves-and-some-black-tape","status":"publish","type":"post","link":"https:\/\/www.homebrewradio.us\/blog\/2018\/02\/19\/a-wonderful-troubleshooting-story-thailand-mixers-a-simpson-260-microwaves-and-some-black-tape\/","title":{"rendered":"A Wonderful Troubleshooting Story — Thailand, Mixers, a Simpson 260, Microwaves, and some Black Tape"},"content":{"rendered":"
<\/a><\/div>\n
<\/div>\n
My old friend was really fortunate to have had such a good Staff Sergeant instructor at Signal School, someone for whom the mixer trig was obviously not enough. And our old friend obviously also benefitted greatly from having had a dad who set him up with a Simpson 260 and some handmade experimental glass diodes. Wow. It all came together with some black tape in Thailand… <\/i><\/b><\/div>\n

<\/b><\/div>\n
\n
Bill,<\/div>\n
<\/div>\n
Enjoyed your latest blog. I remember your asking about mixers years <\/div>\n
ago. I received much the same explanation from a Staff Sergeant <\/div>\n
instructor at Ft. Monmouth in 1967. His example was a mixer with <\/div>\n
diodes, noting the need to have them forward biased by the LO supply. <\/div>\n
We worked out much the same waveforms as shown in your Blog and <\/div>\n
the concept became part of my ‘intuitive’ knowledge.<\/div>\n
<\/div>\n
A few years later I was fighting 120hz hum on the baseband of an IWCS <\/div>\n
microwave system feeding USAF command at the Korat Air Base in<\/div>\n
Thailand. The hum was pretty high level and causing inter-modulation <\/div>\n
problems on the 60 channels of signal sideband suppressed carrier <\/div>\n
being applied to the microwave system.<\/div>\n
<\/div>\n
We ended up with a couple of DCA DoD employees being flown in to help, <\/div>\n
to their credit they were prior service and darn good at what they did. <\/div>\n
After three days of testing all parts of the microwave system with a <\/div>\n
very long distance and long duration phone call to the manufacture in <\/div>\n
Calif, they still had not found the trouble.<\/div>\n
<\/div>\n
I had stayed working with the DCA guys all of the time, during the <\/div>\n
testing I noted the hum seem to lessen in strength with someone standing <\/div>\n
directly behind the radio bay.<\/div>\n
<\/div>\n
I went around to the back and took a close look, Yep! the mixer diodes <\/div>\n
for the baseband order-wire were glass and exposed.<\/div>\n
<\/div>\n
Put a length of black tape over them and the hum went away. Not the <\/div>\n
power supply problem everyone was fixated on, it was diode photo <\/div>\n
sensitivity. I guess we could have just turned off the florescent <\/div>\n
lights too.
<\/smile><\/div>\n
<\/div>\n
When I was 10 years old my father showed me how to use a Simpson<\/div>\n
260 to check diodes and early transistors*. We were on the floor of the <\/div>\n
living room with sunlight streaming in. I saw the forward resistance change<\/div>\n
a lot when the glass diode was in sun light vs shade. It was this memory <\/div>\n
that prompted me to try the black tape.<\/div>\n
<\/div>\n
All the MW systems in SEA later received a MWO to change out the <\/div>\n
order-wire board and I found that the assembly was a non-standard part <\/div>\n
of the microwave system just for military use. Civilian deployment of <\/div>\n
that microwave system had no need for the order-wire.<\/div>\n
<\/div>\n
Thanks for the quick trip, for me anyway, down memory lane and the <\/div>\n
memory of being an electronics tech hero for all of two minutes. The DCA <\/div>\n
guys made me buy the first round at the club. <\/smile><\/div>\n<\/p><\/div>\n
<\/div>\n
73 from an old friend….<\/o:p><\/div>\n","protected":false},"excerpt":{"rendered":"

My old friend was really fortunate to have had such a good Staff Sergeant instructor at Signal School, someone for whom the mixer trig was obviously not enough. And our old friend obviously also benefitted greatly from having had a dad who set him up with a Simpson 260 and some handmade experimental glass diodes. … Continue reading “A Wonderful Troubleshooting Story — Thailand, Mixers, a Simpson 260, Microwaves, and some Black Tape”<\/span><\/a><\/p>\n","protected":false},"author":1,"featured_media":4313,"comment_status":"open","ping_status":"open","sticky":false,"template":"","format":"standard","meta":{"footnotes":""},"categories":[34,426,25,147],"tags":[],"class_list":["post-4312","post","type-post","status-publish","format-standard","has-post-thumbnail","hentry","category-mixer-theory","category-thailand","category-troubleshooting","category-uhf"],"_links":{"self":[{"href":"https:\/\/www.homebrewradio.us\/blog\/wp-json\/wp\/v2\/posts\/4312","targetHints":{"allow":["GET"]}}],"collection":[{"href":"https:\/\/www.homebrewradio.us\/blog\/wp-json\/wp\/v2\/posts"}],"about":[{"href":"https:\/\/www.homebrewradio.us\/blog\/wp-json\/wp\/v2\/types\/post"}],"author":[{"embeddable":true,"href":"https:\/\/www.homebrewradio.us\/blog\/wp-json\/wp\/v2\/users\/1"}],"replies":[{"embeddable":true,"href":"https:\/\/www.homebrewradio.us\/blog\/wp-json\/wp\/v2\/comments?post=4312"}],"version-history":[{"count":1,"href":"https:\/\/www.homebrewradio.us\/blog\/wp-json\/wp\/v2\/posts\/4312\/revisions"}],"predecessor-version":[{"id":4314,"href":"https:\/\/www.homebrewradio.us\/blog\/wp-json\/wp\/v2\/posts\/4312\/revisions\/4314"}],"wp:featuredmedia":[{"embeddable":true,"href":"https:\/\/www.homebrewradio.us\/blog\/wp-json\/wp\/v2\/media\/4313"}],"wp:attachment":[{"href":"https:\/\/www.homebrewradio.us\/blog\/wp-json\/wp\/v2\/media?parent=4312"}],"wp:term":[{"taxonomy":"category","embeddable":true,"href":"https:\/\/www.homebrewradio.us\/blog\/wp-json\/wp\/v2\/categories?post=4312"},{"taxonomy":"post_tag","embeddable":true,"href":"https:\/\/www.homebrewradio.us\/blog\/wp-json\/wp\/v2\/tags?post=4312"}],"curies":[{"name":"wp","href":"https:\/\/api.w.org\/{rel}","templated":true}]}}