Call Search
     

New to Ham Radio?
My Profile

Community
Articles
Forums
News
Reviews
Friends Remembered
Strays
Survey Question

Operating
Contesting
DX Cluster Spots
Propagation

Resources
Calendar
Classifieds
Ham Exams
Ham Links
List Archives
News Articles
Product Reviews
QSL Managers

Site Info
eHam Help (FAQ)
Support the site
The eHam Team
Advertising Info
Vision Statement
About eHam.net

   Home   Help Search  
Pages: Prev 1 [2]   Go Down
  Print  
Author Topic: ceramic disc caps  (Read 2033 times)
G4REK
Member

Posts: 79




Ignore
« Reply #15 on: March 25, 2013, 11:13:21 AM »

Hi,
    Yes the cap goes to relay then to aerial socket
            jim
Logged
WB6BYU
Member

Posts: 13013




Ignore
« Reply #16 on: March 25, 2013, 11:40:01 AM »

Quote from: WB2WIK

If it's a 1000pF capacitor used at 150W output to couple to a 50 Ohm antenna, at that power the capacitor would dissipate about 15W at 28 MHz (Xc = 5.7 Ohms).



One of those senior moments Steve?  Power isn't dissipated in a reactance,
only in the resistive component.
Logged
WB2WIK
Member

Posts: 20542




Ignore
« Reply #17 on: March 25, 2013, 02:42:59 PM »

Quote from: WB2WIK

If it's a 1000pF capacitor used at 150W output to couple to a 50 Ohm antenna, at that power the capacitor would dissipate about 15W at 28 MHz (Xc = 5.7 Ohms).



One of those senior moments Steve?  Power isn't dissipated in a reactance,
only in the resistive component.

Right, of course...I was assuming a very high DF, which is what I've found with Y5E/F/P/U/V ceramics and it "sounds" like that's what he has.

AVX rates DF of their Y5 types at 5% to 7.5% measured at 1 kHz, 100mVrms and 25C.  At increased frequencies, voltages and temperatures, they're worse, in my experience.

I use a Boonton capacitance bridge, a variable frequency signal generator (to test at 1 MHz or 10 MHz), an external bias supply and a hair dryer... Wink  Some of the ceramic disc caps I have (other than NP0 and other TC caps) measure very high DFs, way over 25%, sometimes 50%.  I've had some fail, just testing them.

X7R's a lot better, but I don't think that's what he's using based on the description.
Logged
KE3WD
Member

Posts: 5694




Ignore
« Reply #18 on: March 25, 2013, 04:46:38 PM »

"A sweep tube amp that looks like a damn tube caddy with knobs on it and a point one cap between them and the antenna..." 

heh



Logged
WB2WIK
Member

Posts: 20542




Ignore
« Reply #19 on: March 25, 2013, 06:07:46 PM »

"A sweep tube amp that looks like a damn tube caddy with knobs on it and a point one cap between them and the antenna..." 

heh





Not sure of the reference there, but "10m" amplifiers are often CB amplifiers pressed into 10m service, and many of those designs are silly, whether they used tubes or transistors...or magic.

I'd be especially careful to avoid "Bi-Linear" amplifiers or those designed to be driven by 4W exciters.  And those which are "RF keyed," requiring no DC keying line...


Logged
G3RZP
Member

Posts: 4362




Ignore
« Reply #20 on: March 26, 2013, 10:13:29 AM »

You need a low loss dielectric there. NP0 caps a re a bit expensive at 1nF, but you used to be able to get them. Probably worth putting four 270pF NP0 in parallel.
Logged
AC7ZN
Member

Posts: 41




Ignore
« Reply #21 on: March 28, 2013, 06:22:17 AM »

Although the ceramic dielectric hasn't changed much, manufacturers are now able to make it with fewer defects and porous 'holes' that can cause leakage or breakdown, especially at high humidity (assuming the capacitor is not sealed).  Because of this they are able to use thinner dielectric and smaller plate size for a given capacitance and working voltage.
73,
Glenn AC7ZN
 
Logged
Pages: Prev 1 [2]   Go Up
  Print  
 
Jump to:  

Powered by MySQL Powered by PHP Powered by SMF 1.1.11 | SMF © 2006-2009, Simple Machines LLC Valid XHTML 1.0! Valid CSS!