[Antennas] Trap design, how far from operating freq, should I hit?

[john]

Buck, and others,

Thanks for the replies so far. I've been able to move it fine. 
I just am curious where to resonate it. I note that the traps (they're 
15m ) all actually resonate about 21.5 Mhz according to my Millen 
GDO and counter

I guess I could figure the ratio between 21.5 and say, 21.25 and use
the same ratio at 12m. 

Nothing ventured, etc....

Interesting to note that the trap is wound with what appears to be 
about #12 Aluminum wire on a turned form,subsequently swathed in 
Qdope/Lacquer.

Thanks!
John



On 3 Apr 2005 at 19:18, Buck - N4PGW wrote:

I haven't seen that particular trap, but on the Taylor Radio and Hustler
trap verticals as well as on many beam designs, the trap consists of a coil
and a capacitor, the capacitor being the aluminum can shorted to one side
and overlapping the coil.  You may be able to trim the trap enough by
shortening the coil alone.  However, if that doesn't work, consider
adjusting the coil up or down a bit if it doesn't work.

Buck
N4PGW


> -----Original Message-----
> From: antennas-bounces at mailman.qth.net [mailto:antennas-
> bounces at mailman.qth.net] On Behalf Of john
> Sent: Sunday, April 03, 2005 6:14 PM
> To: antennas at mailman.qth.net
> Subject: [Antennas] Trap design, how far from operating freq, should I
> hit?
> 
> I'm modifying a 15m Cushcraft trap into a 12m trap by removing
> turns on the coil. I have read that it's better to design the trap to
> be resonant at a different frequency than the target (operating
> frequency) to minimize losses.  I'd like to understand why this is so.
> 
> I'm planning on making the trap resonant above the operating
> target, and adding a bit more length to the element "inside" the
> traps,to resonate the system at my operating freq.
> 
> My question is, how far off the operating freq should I build
> the traps for?
> 
> My goal is a 12 and 17m  shortened dipole (or 2 el yagi, should
> this work).  An understanding of why a trap resonant at the
> operating frequency is more lossy than otherwise, would be a plus.
> 
> Thanks!
> John
> 
> 
> 
> 
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