As I’ve mentioned, I am building a superhet receiver around the beautiful National Radio gearbox\/dial that Armand WA1UQO gave me. First step was to build the VFO. Before I started, I went back to Doug DeMaw’s books and read his words of wisdom on how to build stable VFOs. I followed his advice: <\/p>\n
— Air core coils.
— Tuning capacitors with bearings at both ends.
— NPO fixed capacitors.
— All frequency determining parts in a separate box
— Run the oscillator stage at lower voltage (6 volts)
— Stable solid physical construction.
— One-sided PC boards. <\/p>\n
I went a bit further. I wound the main coil on a cardboard tube from a coat hanger. I coated it with several layers of clear nail polish. I glued it down with a generous dose of gorilla glue.<\/p>\n
There are some fixed caps in the circuit. I didn’t want them physically hanging off other parts, so I used bits of balsa wood to support them. <\/p>\n
I put the actual oscillator stage in its own Altoids tin and attached this tin to the bot that held the main coil and capacitor. I put the 6 volt Zener diode and its dropping resistor on the outside of the box to minimize heating. The buffer and amplifier went into another Altoids tin. I used a wooden grilling plank from Whole Foods as my base. <\/p>\n
At first, Armand’s gear box and reduction drive didn’t seem wo work very well. There seemed to be a lot of “play” in the mechanism. Some words of wisdom from Pete N6QW and the blog Dave AA7EE provided the solution. There is a spring in the gearbox that hold the teeth of the gears together and prevents the kind of play that I encountered. With guidance from Dave, I was able to put some adiditonal tension on the spring and the gears. This resolved the play problem.<\/p>\n","protected":false},"excerpt":{"rendered":"
As I’ve mentioned, I am building a superhet receiver around the beautiful National Radio gearbox\/dial that Armand WA1UQO gave me. First step was to build the VFO. Before I started, I went back to Doug DeMaw’s books and read his words of wisdom on how to build stable VFOs. I followed his advice: — Air … Continue reading “Building a Very Stable VFO (With Coils and Capacitors)”<\/span><\/a><\/p>\n","protected":false},"author":1,"featured_media":0,"comment_status":"open","ping_status":"open","sticky":false,"template":"","format":"standard","meta":{"footnotes":""},"categories":[1],"tags":[],"class_list":["post-2484","post","type-post","status-publish","format-standard","hentry","category-uncategorised"],"_links":{"self":[{"href":"https:\/\/www.homebrewradio.us\/blog\/wp-json\/wp\/v2\/posts\/2484","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=2484"}],"version-history":[{"count":0,"href":"https:\/\/www.homebrewradio.us\/blog\/wp-json\/wp\/v2\/posts\/2484\/revisions"}],"wp:attachment":[{"href":"https:\/\/www.homebrewradio.us\/blog\/wp-json\/wp\/v2\/media?parent=2484"}],"wp:term":[{"taxonomy":"category","embeddable":true,"href":"https:\/\/www.homebrewradio.us\/blog\/wp-json\/wp\/v2\/categories?post=2484"},{"taxonomy":"post_tag","embeddable":true,"href":"https:\/\/www.homebrewradio.us\/blog\/wp-json\/wp\/v2\/tags?post=2484"}],"curies":[{"name":"wp","href":"https:\/\/api.w.org\/{rel}","templated":true}]}}