Hy-Gain Part Number 878749, 10 meter trap:
I removed the cylindrical sheild (outer 1 5/8" tubing), sawed the 7/8"
tubing extensions down to 1" long on each end of the coil, and attached
pigtail wires to the coil terminals. I used 2 inch 10 AWG insulated wires
for the pigtails initially, then used 4 inch 10 AWG insulated wires later.
There was very little difference. The coil itself is made from .102" OD
aluminum wire, coil diameter is 1", coil length is 2", number of turns is
17, and form is polypropylene with grooves.
Using a Boonton 260-A Q-meter, Q=240 @ 17 MHz with C=32 pF.
Using an HP 4342A Q-meter, Q=300 @ 17 MHz with C=32 pF.
With the frequency set to "L", L=2.44 uH.
A 1.625" OD by 4.5" long shield was placed over this assembly, with the
shield shorted to one end of the coil by a bent strap (part of the shield).
Equal length pigtail wires come out each end. A polypropylene spacer
(onion-ring) was placed at the open end for centering.
Using the HP 4342A Q-meter with this assembly, Q=210 @ 17 MHz with C=43 pF.
With the frequency set to "L", L=1.78 uH.
A frequency of 17 MHz was used because a resonance could not be obtained at
28 MHz. The minimum capacitance in these Q-meters is approx. 30 pF.
These measurements are close to what could be expected using the graph on
page 6-3 of the 6th edition of Reference Data for Radio Engineers.
(Winding Length/Winding Dia = 2, Winding Dia/Shield Dia = 0.65, reduction
in inductance = 65%)
I will measure the 15 meter traps as time permits.
73 Roger WB0DGF
Telex Communications, Inc. (Hy-Gain)
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