Amateur Radio Stack Exchange
Amateur Radio Stack Exchange

Questions tagged [capacitance]

16 questions
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What limits a PIN diode or varicap from being used in a "Software Defined [Radio] Filter"?

A PIN diode varies its capacitance based on a DC bias, and a Varicap exhibits this effect even more clearly. What limits the use of "solid state variable capacitors" like these for dynamically filtering (low power/received) RF signals? The question…
natevw - AF7TB
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RigExpert AA-35 - Interpreting The Information

I have a new RigExpert AA-35 antenna analyzer. 1st one I have had & 1st time trying to use an analyzer on an antenna. My questions are very basic and general, but I am having difficulty in Googling for answers. Hope someone can help, or direct me…
B. Varner
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How to reduce VFO sensitivity to the hand capacitance?

I got a little tired of Si5351 and decided to build an analog CW transceiver. It's almost done and works pretty well. However, I discovered one problem. When I reach the VFO control with my hand the frequency shifts a little, about 100 Hz or so.…
Aleksander Alekseev - R2AUK
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Feed-through Capacitors

I'm in the "information gathering" phase of a RF Power Meter project and the design I fancy (W7ZOI Power Meter) calls for a feed-through capacitor at the output port. I understand that a feed-through capacitor is essentially a "trap" or low-pass…
Buck8pe
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How to choose right inductors for a matching circuit

I would like to chose an inductor to make a matching circuit. Operating frequency is 6.1 GHz. I am more concerned with self resonance frequency and Q of an inductor. Would an inductor with SRF > 7 GHz and Q > 10 be okay at above frequency?
Shiva Mudide
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How can I determine/measure power rating of a DIY air capacitor?

I've build an air capacitor like the one described in this article, although I used 1 mm thick single side copper boards (FR4) instead of solid copper sheets. I would like to use such capacitors in my next projects, e.g. an antenna tuner and a…
Aleksander Alekseev - R2AUK
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interdigital (finger) capacitor bank for fine tuning of differential loop antenna

I am attempting to implement a PCB trace antenna; namely the sample in this document. Thing is the 1.17 pF for Cp1 is quite hard to achieve in a cost efficient manner with 0603 caps (I loath those smaller beasts that not many hands can solder), and,…
kellogs
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Are the voltage ratings on Vacuum Variable Capacitors RMS or Peak

I'm building a magnetic loop antenna and was wondering if the voltage ratings on the vaccuum variable capacitors I have are: RMS Peak to Peak Peak other? I have been looking at this wonderful magnetic loop calculator to help choose a capacitor…
Arthur
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recommended capacity bottom-hat clearance above metal roof

In a few days I'm expecting to mount a Cushcraft R7000 multi-band (HF) vertical antenna on top of a metal mast that will be attached to the outside wall of a large metal shed. The aim is to have the base of the antenna stick out above the roof of…
captcha
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What do old unit abbreviations like "mfd" and "kc" mean, and where did they come from?

I saw a recent answer that mentioned "mfd" as a unit of capacitance, and I can recall having seen that term in old schematics and ham radio articles. I've also seen other non-SI unit abbreviations, such as "kc" on old equipment and in old articles.…
rclocher3
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How to estimate or measure the max voltage of an air variable capacitor

I have a big box of air-variable capacitors I inherited and want to see if I can use one of them for a low power magnetic-loop antenna for 30m digital. How can I figure out if any of them have a high enough maximum voltage? If I do this by trial…
Arthur
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How to eliminate alternator whine?

On my car's LW receiver, I have a severe case of alternator whine, especially when the headlights are on. It has become worse over time. I have read that capacitors might help. However, two things remain unclear to me: Of what value should these…
on4aa
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Identify these components

First post here yay! I am repairing Shengda sdhf dual band antenna (looks similar to a Comet x50) it showed a SWR of >3 on both UHF and VHF. I opened it up and the only connection I could see from the centre core to the antenna element is two…
Gerrie
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Is it possible to measure the capacitance of a gamma rod? Gamma match

I was wondering if it is possible to measure the capacitance of a gamma rod using an L/C meter. I tried to measure one by clipping one of the alligator clips on the outer aluminum tube and the other one on the inner core of an insulated piece of…
Electro Jo
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change LC parameter digitally

LC circuit is the main element of every frequency generator, I intend to make an FM transmitter, but many opensource circuit use analog variable L or C part to set and adjust the target frequency My question is : is there any IC or digital circuit…
Mehrdad Hrsk
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