[Lowfer] LF Lop Antennas

[Peter Cranwell]

I have a working Heath Q meter which I callibrated.  If anyone is interested 
in it, I'll give it up.

Pete
----- Original Message ----- 
From: <ToddRoberts2001 at aol.com>
To: <lowfer at mailman.qth.net>
Sent: Monday, August 25, 2008 1:35 PM
Subject: Re: [Lowfer] LF Lop Antennas


> In a message dated 8/25/2008 10:39:24 A.M. Eastern Daylight Time,
> kc0vsj at yahoo.com writes:
>
> A good page wint a nice colleciton of other links at the bottom. One thing 
> I
> am trying to get a handle on is the relative Q of various types of 
> capacitors
> - Air variable, Poly variable as in what Doug Hendricks has,  mica, mylar,
> polystyrene etc.   Does anybody have a resource on this?  So far  I have 
> seen
> air variable as in the 1500' range and mica at 1200.
>
>
>
> Crystal radio set builders are always interested in the highest Q
> capacitors. There doesn't seem to be very much information published on 
> the  actual Q of
> different types of capacitors. The best way to determine the best  kind of
> capacitor is to resonate them with an actual coil on a good Q meter  and 
> look
> for highest Q readings. The Hewlett-Packard 4342A Q meter is one of the 
> best
> for this.
>
> There is no set Q with any type of capacitor as different batches and 
> dates
> from factory production can be different. Polystyrene caps are usually 
> better
> than fixed Mica. Some of the newer ceramic chip capacitors have extremely
> high  Qs. Also the type of insulation used in a variable capacitor can 
> affect Q.
> The  more common air-variables with phenolic insulation are worse than the
> military  types with ceramic insulation. Also some types of air variables 
> are
> silver  plated which increases Q. The consensus is that the silver plated 
> 500pF
> air  variable used in the URM-25 signal generator is one of the best. 
> Crystal
> set  builders nickname it the Holy Grail Cap.
>
> Check with some crystal radio set groups to see what capacitors they are
> using.
>
> 73 Todd WD4NGG
>
>
>
>
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