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 Post subject: Remote tuner for a loop antenna
PostPosted: May Thu 09, 2019 7:43 am 
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Joined: Aug Sat 13, 2016 6:03 am
Posts: 181
Location: Ashland Oregon
I have a loop which tunes 40m and 80m and have been contemplating a method to remotely control the 700pf variable capacitor. A friend told me of a solid state devise that changes capacitance as the controlling voltage changes. I've never heard of anything like this. Do you think it might have the range of my current capacitor? I have a gut feeling that answer is NO. I could do some research on this if I knew the formal name of this thing. Thanks for furthering my education on this subject.


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 Post subject: Re: Remote tuner for a loop antenna
PostPosted: May Thu 09, 2019 11:38 am 
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Joined: Jul Mon 26, 2010 8:30 pm
Posts: 26797
Location: Annapolis, MD
Varactor diode---also sometimes called a "varicap"

https://www.mouser.com/Semiconductors/D ... _/N-ax1mn/

Use their filtering tools to find the desired capacitance and other parameters

_________________
-Mark
"Measure voltage, but THINK current." --anon.


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 Post subject: Re: Remote tuner for a loop antenna
PostPosted: May Thu 09, 2019 3:13 pm 
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Joined: Aug Thu 20, 2015 3:09 pm
Posts: 1246
Location: Albion, CA, USA, 95410
I don't think varactors usually go that high in pF but I could be wrong. Is the antenna for receive only? That makes a difference. What type of cap are you using now, plate cap, vacuum cap? How far is the variable cap from the shack? There are all sorts of ways to attach a motor, stepper motor, servo but what is best or easiest depends on the situation.


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 Post subject: Re: Remote tuner for a loop antenna
PostPosted: May Thu 09, 2019 6:55 pm 
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Joined: May Tue 30, 2006 4:46 pm
Posts: 10000
Location: Santa Rosa, CA
Varactors were made with >300 pF capacitance to use in tuning low cost solid state AM radios.

http://www.kitsandparts.com/MVAM109.pdf

Rich


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 Post subject: Re: Remote tuner for a loop antenna
PostPosted: May Thu 09, 2019 7:49 pm 
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Joined: Jan Thu 01, 1970 1:00 am
Posts: 4134
You can use varactors in parallel, but your range is limited unless you use series/parallel switched by relays or similar.

As an alternative, use a motarized varicap.

These are sold all over the internet. Ignore the volume control circuitry and use a shaft coupler to put on your varicap.

https://www.ebay.com/itm/9V-Infrared-Re ... SwjXNbESAy


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