[Hallicrafters] Capacitor self resonance

[Peter Bertini]

I thought I would offer up my findings for series resonance frequencies for
several caps I tested in the shop. I didn’t have much luck with the grid
dipper method, so I emulated the following HP setup as close as I could:



http://www.home.agilent.com/upload/cmc_upload/All/exp79.pdf?&cc=US&lc=eng



Equipment used was one of the shop’s HP-141T generators with the 8553B RF
deck and companion 8443A tracking generator. A photo of the bench setup and
improvised test jig is here:



http://i117.photobucket.com/albums/o46/radioconnection/DSCF1043.jpg

If the premise for this setup is flawed, I'd appreciate feedback.


I didn’t have a large selection of disk ceramics, but here is what I
measured.



110pF ceramic disk, NPO, full leads    62 MHz

110pf ceramic disk NP0, .5” leads  82 MHz



All caps below tested with .5 inch leads, unless noted.



.01 uF Mylar, film, etc. test results

10,000pF SM, 5%  10.19 MHz

.01 uF 400 VDC marked SBE7716P    10.0 MHz

.01 uF 200 VDC marked 225PX    10.4 MHz

.01 uF 630 VDC  NTE or Panasonic,  10.6 MHz

.01 uF 1600 VDC  10.31 MHz



.01 disk ceramic capacitor test results

.01 uF UL rated safety cap, disk 12.8 MHz

.01 uF 1.4kV disk  11.46 MHz (longer leads)

.01 uF 1.4kV disk   marked Z5U, 10.912 MHz shorter leads

.01 uF 500 V disk, marked KCK brand  9.1 MHz



I didn’t note a wide spread for any of the .01 uF caps tested;

The series resonances pretty much all clustered in the 10 MHz region.



Pete


On Sun, Jan 2, 2011 at 6:39 PM, Richard Knoppow <1oldlens1 at ix.netcom.com>wrote:

>     I got curious so I measured a 0.002uf 600V film cap
> using a Boonton 250 RX-Meter. This device is well suited to
> measuring low-Q resonators and goes up to 250mhz. The
> reactance range is limited but around resonance there is
> little reactance. The RX meter is a Schering bridge and
> measures _series_ resonance. This is unlike the Q-Meter,
> which measures parallel resonance and is best suited to
> high-Q reactances.
>     I found that the self resonance of this capacitor
> appears to be around 147mhz. Below that, say at 145mhz the
> sense of the X is still capacitive, at 150mhz it becomes
> inductive. I did not try to find the exact resonance since
> that would have required many successive measurements but I
> think this is close enough to give some idea of performance.
>     The cap is in a dipped package with radial leads. The
> leads are relatively short. the body of the cap is perhaps
> half an inch long and less than 1/4" wide, quite thin. I
> have other caps and will try them later. Its obvious that
> this cap would be an effective by pass cap in the
> "communication" range, certainly up to 30 mhz and probably
> up to 65mhz.
>     I have film caps with values closer to 0.02 and 0.05.
> Likely they are different. I also have some ceramic caps. I
> will try these in the near future and report back on what I
> find.
>     I am hors de combat as far as detecting piezoelecric
> effects by ear since my hearing has deteriorated
> significantly in recent years. I have not yet tried looking
> on a scope to see if there is any output from mechanical
> excitation but suspect there will be. If one is present the
> other will be too.
>
>
> --
> Richard Knoppow
> Los Angeles
> WB6KBL
> dickburk at ix.netcom.com
>
>
>
>
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