Feed-through capacitor?

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larry955
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Feed-through capacitor?

Post by larry955 »

I am trying to build a "bug-detector" from a daigram I found somewhere. It calls for a .001 ufd "feed-through capacitor" This is something new to me and would like to know the role it plays when used just before the antenna and soldered to a shield. also where are they available from?<p>larry955
bodgy
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Re: Feed-through capacitor?

Post by bodgy »

Unhelpfully I have a whole bag of them, helpfully<p>they are a capacitor often used in SW/HF RF to couple sensitive component modules from each other.<p>For example some SW/VHF radios might have the oscillator stage in a shielded case (to stop nearby circuitry interfering or being interefered with). To attach the power source and signal line to the module you would have to drill holes in the shielded case. Into the power supply hole you would insert a feed through cap- it has two radial leads and a metal type body with a groove running around its circumference, the case fits in the groove(tightly), and the circuit either side is soldered to the leads.
In your particular circuit you may or maynot have a phantom power supply to the aeriel.<p>In the US I am not sure where they would be purchased from, but I suggest looking at component suppliers to the Ham radio fraternity.
Have a look in a Short Wave or Ham TV magazine.<p>colin<p>PS. Just to make you all jealous I am the proud owner of a triple gang 365pF Jackson variable cap- one day I'll get round to using it.<p>[ August 23, 2002: Message edited by: bodgy ]</p>
On a clear disk you can seek forever.
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Edd
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Re: Feed-through capacitor?

Post by Edd »

Larry.....Agent955 :
Feed thru caps...eh.
Three things come to mind. In the very old..... post-Neanderthal....pre Cro magnon vintage TV tuners of vacuum tube days, they used them in some stages and mainly on the terminal inputs of B+,fil,AGC terminations....so there would be a salvage source for you. <p>Secondarily you can still get them at reasonable prices at:<p>http://www.debcoelectronics.com/
http://www.fairradio.com/capaci.htm <p>Final possibility: I'm assuming you're either metal compartmental sectionizing or using pcb mat'l shielding. I believe you wud be ok with taking the feed thru wire either insulated or bare with form fitting teflon insulation sphagetti and making the tightest clearance hole possible and then have (2) 470 pf CK05 style monolithic block caps, radially opposed ,using almost zero lead length connected to the central wire for bypassing just as it passes thru the hole.The caps rear leads are to be immediately soldered to gnd plane. If U have surface mount chip caps available, the same way, except it wud
be even more compact.<p>I also have a box of them .....but putting my hands on them quickly....??? And if I remember correctly Bodgy is quite distant. <p>PS Bodge.......how about a quad ganged 365 unit.......but I used it in a low dist Wien Bridge Osc I built with it. BUT......I still have a quad 420 unit....Neither were Jackson's but well known older USA manuf units, but the brand names won't come to mind.<p>73's de Edd<p>[email protected] (Interstellar~~~~Warp~~~~Speed)
[email protected] (Firewalled-Spam*Cookies*Crumbs)<p> :)
larry955
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Re: Feed-through capacitor?

Post by larry955 »

bodgy, Thanks a lot for the help. Iam a subscriber to nuts&volts and poptronics both of which I enjoy a lot, I wish I had developed the intrest when I was young.
Hope one day I can return the favor.
larry955
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Re: Feed-through capacitor?

Post by larry955 »

eddw35 Guess it was the numerical suffix that gave me away huh? Fact is I am a retired Private Investigator but I never even made the link between that and the 955 that was auto-issued or at least sugggested by my isp or mail. This has really been great. Not only informative due to your generous nature and others like you but flat entertaining. I checked out the previous messages and replies and got a great kick out of the guy wanting to break into "phreaking" and "Trunked" systems. also the cat who wondered just how much voltage and current a man take if you wired his car to the HV system under the hood. seriously, thanks a lot for taking the time to relpy to a novice
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