Topics

CAP VALUE

pileupjunkie <beargyrils@...>
 

Hello,
I came upon a cap rated 25 to 420-pf 2,200 volts, with a plate spacing of .030.
Will this cap carry 30 WATTS  CW with no problem?
Picture is attached.
Thank you
BOB AF2DX

beargyrils@...

WA8LMF
 

On 5/4/2018 5:59 PM, pileupjunkie via Groups.Io wrote:
Hello,
I came upon a cap rated 25 to 420-pf 2,200 volts, with a plate spacing of .030.
Will this cap carry 30 WATTS  CW with no problem?
Picture is attached.
Thank you
BOB AF2DX

It's not a matter of POWER handling.  It's limited by VOLTAGE breakdown across the air gap between the plates. You specified it as being 2200 volts.    In turn, the RF voltage this cap will experience will be determined by the kind of matching network you build with it, the nature of what you are trying to match/feed (i.e. is it a high-impedance end-fed half-wave, or an easy-to-match quarter-wave, or something in-between).

In practice, it is very unlikely that any kind of real-world network you build with this device would remotely challenge the breakdown ratings of this cap at only 30 watts.



--

Stephen H. Smith    wa8lmf (at) aol.com
Skype:        WA8LMF
EchoLink:  Node #  14400  [Think bottom of the 2-meter band]
Home Page:          http://wa8lmf.net


 Long-Range APRS on 30 Meters HF
    http://wa8lmf.net/aprs/HF_APRS_Notes.htm

High Performance Sound Systems for Soundcard Apps
   http://wa8lmf.net/ham/imic.htm
   http://wa8lmf.net/ham/uca202.htm

"APRS 101"  Explanation of APRS Path Selection & Digipeating
  http://wa8lmf.net/DigiPaths



pileupjunkie <beargyrils@...>
 

Sorry,
My fault and being worried about eye surgery
The CAP I attached is for a MAG LOOP
No cap spacing is given but it looks like it will do CW at 30 WATTS.
I thought I sent you this.

Hello,
I am building a mag loop and I spotted this dual gang cap on your site but does  not have the cap spacing.
Do you know if this will carry 30 WATTS CW?
Thank you
BOB AF2DX



From: BOB AF2DX <beargyrils@...>
To: beargyrils <beargyrils@...>
Sent: Fri, May 4, 2018 5:46 pm
Subject: Re: https://www.rfparts.com/47-887.html

47-887 Low Shaft Friction Variable Capacitor, 22-430, 25-457 uf

Regular Price: $59.95
SPECIAL PRICE $49.95
add to cart
47-887 Low Friction Shaft Variable Capacitor, 22-430, 25-457 uf, MFR: Cardwell (SEE NOTES IN DESCRIPTION)



-----Original Message-----
From: BOB AF2DX <beargyrils@...>
To: beargyrils <beargyrils@...>
Sent: Fri, May 4, 2018 1:08 am
Subject: https://www.rfparts.com/47-887.html

https://www.rfparts.com/47-887.html     <----CLICK ON THIS LINK
BOB AF2DX
beargyrils@...


-----Original Message-----
From: WA8LMF via Groups.Io <wa8lmf@...>
To: CrossCountryWireless <CrossCountryWireless@groups.io>
Sent: Fri, May 4, 2018 8:14 pm
Subject: Re: [CrossCountryWireless] CAP VALUE

On 5/4/2018 5:59 PM, pileupjunkie via Groups.Io wrote:
Hello,
I came upon a cap rated 25 to 420-pf 2,200 volts, with a plate spacing of .030.
Will this cap carry 30 WATTS  CW with no problem?
Picture is attached.
Thank you
BOB AF2DX

It's not a matter of POWER handling.  It's limited by VOLTAGE breakdown across the air gap between the plates. You specified it as being 2200 volts.    In turn, the RF voltage this cap will experience will be determined by the kind of matching network you build with it, the nature of what you are trying to match/feed (i.e. is it a high-impedance end-fed half-wave, or an easy-to-match quarter-wave, or something in-between).

In practice, it is very unlikely that any kind of real-world network you build with this device would remotely challenge the breakdown ratings of this cap at only 30 watts.



--

Stephen H. Smith    wa8lmf (at) aol.com
Skype:        WA8LMF
EchoLink:  Node #  14400  [Think bottom of the 2-meter band]
Home Page:          http://wa8lmf.net


 Long-Range APRS on 30 Meters HF
    http://wa8lmf.net/aprs/HF_APRS_Notes.htm

High Performance Sound Systems for Soundcard Apps
   http://wa8lmf.net/ham/imic.htm
   http://wa8lmf.net/ham/uca202.htm

"APRS 101"  Explanation of APRS Path Selection & Digipeating
  http://wa8lmf.net/DigiPaths