[TowerTalk] FW: Trap ID

[Jim Hargrave]

I have a mobile antenna that uses a similar coil.
It is a single center load but has 2 coils inside. It is setup the same configuration as the RV-3C.
It covers 10/15/20m. It is approx. 8 ft. tall
I have had 2 of these for about 35 years, but have never been able to find a model number. 

73, Jim – w5ifp at gvtc.com

>> -----Original Message-----
>> From: TowerTalk [mailto:towertalk-bounces at contesting.com] On Behalf Of
>> Matt
>> Sent: Tuesday, December 9, 2014 10:24 PM
>> To: towertalk at contesting.com
>> Subject: [TowerTalk] FW: Trap ID
>> 
>> Mosley TA33 trap explanation:
>> 
>> To the best of my knowledge, this is how it works...
>> 
>> Inside the trap there are coils on each end.   The inner element inserts into
>> coil form such that the aluminum trap cover forms a coaxial capacitor along
>> their overlapping length.  This is wired in parallel with the inner coil to form a
>> resonant trap for the 10m band.   On 15m, the 10m trap becomes a net
>> lump-sum inductance, thereby shortening the resonant length of the 15m
>> section.   The length of the aluminum trap cover is cut to resonant the
>> antenna on 15m.   The outboard element tip inserts into the other end of
>> the coil form such that the aluminum trap cover also forms a coaxial
>> capacitor along their overlapping length.  This is also wired in parallel with
>> the outer coal to form the 15m resonant trap.   On 20m, both the 10m trap
>> and the 15m trap both become net lump-sum inductances which shorten
>> the resonant length of the 20m section.   The outer element length is then
>> selected to be resonant on the 20m band.
>> 
>> Stuff that can go wrong with the traps:
>> 
>> 1. Coil form cracks and arcs over to the inner element at high voltages (high
>> power).  Be aware that the coil form is also a structural part of the element -
>> it transfer bending moments from wind loadings or other forces acting on
>> the outer element tip.
>> 2. RF contact quality where the end of the coil connects to the outer trap
>> cover degrades (usually from oxidation - keep it clean and apply some
>> penetrox or similar at the connection).
>> 3. Overheating the coil melts the coil form and physically changes the shape
>> of the coil enough to move the resonance.
>> 4. Coil wire open circuits at the end where it is riveted to the inner element.
>> 5.  Insects, or their residue, become moist with humidity (or infiltrated rain)
>> and short out sections of coil winding, changing the resonance.
>> 6. And my favorite...   the element is mounted upside down such that the
>> trap drains are at the top....  the trap fills up with rain water and....
>> 
>> BTW, the traps for TA-series are different for each element.   They can be
>> identified (director, driver, reflector) by counting the number of turns on
>> the coils.
>> 
>> Hope this is helpful and good luck on your project.
>> 
>> 73
>> Matt
>> KM5VI
>> 
>> 
>> -----Original Message-----
>> From: TowerTalk [mailto:towertalk-bounces at contesting.com] On Behalf Of
>> Wilson
>> Sent: Tuesday, December 09, 2014 9:43 PM
>> To: towertalk
>> Subject: [TowerTalk] Trap ID
>> 
>> Someone suggested Mosley, which seems correct.
>> Their trap design: http://www.mosley-electronics.com/pdf/trapdesigns.pdf
>> 
>> A tribander with only six traps:  http://www.mosley-
>> electronics.com/pdf/amateur/cl33m.pdf
>> 
>> I don’t understand the traps.  There are two coils in each, but I don’t see
>> how that isolates sections for the bands.
>> The explanation is incomplete, to say the least.
>> 
>> So far, no detailed explanation has appeared from googling.
>> 
>> Thanks,
>> WL
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