{"id":630,"date":"2011-04-28T21:25:50","date_gmt":"2011-04-29T02:25:50","guid":{"rendered":"http:\/\/w0ep.us\/OM\/?p=630"},"modified":"2011-04-28T21:33:34","modified_gmt":"2011-04-29T02:33:34","slug":"testing-a-coaxial-resonator","status":"publish","type":"post","link":"http:\/\/w0ep.us\/OM\/?p=630","title":{"rendered":"Testing a coaxial resonator"},"content":{"rendered":"

[Yesterday’s run: Watson road 3.5 miles]<\/p>\n

[Today’s run: Limerock Road 4.0 miles]<\/p>\n

I have been a bit worried since I brought home this big conglomeration of VHF resonators, isolators, harmonic filters, etc.\u00a0 One worry that I could do something about was to get one of the resonators and try it out at 2-meter frequencies.<\/p>\n

I had been racking my brain for a way to do that.\u00a0 I have VHF transmitters for the amateur bands.\u00a0 So I started out with that.\u00a0 But I was not sure which way to tune the thing.\u00a0 And the band-pass notch is so sharp that I was likely to miss it.\u00a0\u00a0 What I needed was a wide-ranging signal source.<\/p>\n

So then I thought about my old grid-dip meter.\u00a0 A grid dip is an oscillator.\u00a0 You hold it close to a resonate circuit, adjust the oscillator frequency and look for a dip.\u00a0 A dip means that you have found the point of resonance.\u00a0 The way the circuit is built that causes a “dip” in the “grid”, hence it is a grid-dip meter.\u00a0 Sure enough, my GDO has the capability to go up to about 450 Mhz.<\/p>\n

I put an antenna-ish loop on one side of my VHF resonate cavity and on the other side I put a 50 Ohm dummy load.<\/p>\n

I played around with that a little bit trying to couple the GDO and the loop, and I could not find a dip.\u00a0 The problem there was that the notch is so sharp and the GDO tunes over a wide range, so I was missing it.\u00a0 In my experience using the GDO in a dipper manner is hit and miss.\u00a0 Sometimes I find the dip and sometimes I don’t.<\/p>\n

Then I finally had an idea that worked.\u00a0 I hooked up a sensitive RF power meter\u00a0 (the blue box on the bench in my picture) in place of the 50 Ohm dummy load.\u00a0 I just used the GDO as an oscillator and didn’t bother to look for the dip.\u00a0 It worked.\u00a0 I could see a very sharp spike tuning past one particular frequency.\u00a0 I adjusted the tuning plunger and found that I could easily put this VHF resonator in the 2-meter amateur band, or quite a bit below or above.\u00a0 I ended up tuning from about 130 Mhz to above 180 Mhz and I did not go to the uttermost end of travel of the tuning plunger in either direction.<\/p>\n

So that was kind of fun. I figured out a way to roughly measure the resonate frequency. And I confirmed that these resonators work on the 2-meter ham band.\u00a0 And–I now know that I can use my GDO as a test oscillator well into the VHF band\u00a0 (Not as good as a real signal generator, but it worked.)<\/p>\n

Here’s the picture of my lash-up.\u00a0 The beige box is the GDO.\u00a0 The black canister thing is the VHF cavity\u00a0 (it is about 3 feet high in this picture).\u00a0 My single-wire antenna-ish loop is hanging out of the left port on top of the can.\u00a0 You can’t see the output port, it is behind the GDO.<\/p>\n

\"\"<\/a><\/p>\n","protected":false},"excerpt":{"rendered":"

[Yesterday’s run: Watson road 3.5 miles] [Today’s run: Limerock Road 4.0 miles] I have been a bit worried since I brought home this big conglomeration of VHF resonators, isolators, harmonic filters, etc.\u00a0 One worry that I could do something about was to get one of the resonators and try it out at 2-meter frequencies. I […]<\/p>\n","protected":false},"author":1,"featured_media":0,"comment_status":"open","ping_status":"open","sticky":false,"template":"","format":"standard","meta":{"footnotes":""},"categories":[5],"tags":[],"class_list":["post-630","post","type-post","status-publish","format-standard","hentry","category-ham-radio"],"_links":{"self":[{"href":"http:\/\/w0ep.us\/OM\/index.php?rest_route=\/wp\/v2\/posts\/630","targetHints":{"allow":["GET"]}}],"collection":[{"href":"http:\/\/w0ep.us\/OM\/index.php?rest_route=\/wp\/v2\/posts"}],"about":[{"href":"http:\/\/w0ep.us\/OM\/index.php?rest_route=\/wp\/v2\/types\/post"}],"author":[{"embeddable":true,"href":"http:\/\/w0ep.us\/OM\/index.php?rest_route=\/wp\/v2\/users\/1"}],"replies":[{"embeddable":true,"href":"http:\/\/w0ep.us\/OM\/index.php?rest_route=%2Fwp%2Fv2%2Fcomments&post=630"}],"version-history":[{"count":5,"href":"http:\/\/w0ep.us\/OM\/index.php?rest_route=\/wp\/v2\/posts\/630\/revisions"}],"predecessor-version":[{"id":636,"href":"http:\/\/w0ep.us\/OM\/index.php?rest_route=\/wp\/v2\/posts\/630\/revisions\/636"}],"wp:attachment":[{"href":"http:\/\/w0ep.us\/OM\/index.php?rest_route=%2Fwp%2Fv2%2Fmedia&parent=630"}],"wp:term":[{"taxonomy":"category","embeddable":true,"href":"http:\/\/w0ep.us\/OM\/index.php?rest_route=%2Fwp%2Fv2%2Fcategories&post=630"},{"taxonomy":"post_tag","embeddable":true,"href":"http:\/\/w0ep.us\/OM\/index.php?rest_route=%2Fwp%2Fv2%2Ftags&post=630"}],"curies":[{"name":"wp","href":"https:\/\/api.w.org\/{rel}","templated":true}]}}