Hy-Gain Part Number 878637, 15 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 used 4 inch 10 AWG insulated
wire pigtails. The coil itself is made from .102" OD copper wire, coil
diameter is 1", coil length is 3.75", number of turns is 30, and form is
polypropylene with grooves.
Using an HP 4342A Q-meter, Q=330 @ 13 MHz.
With the frequency set to "L", L=4.7 uH.
A 1.625" OD by 5.75" 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 4" 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=235 @ 13 MHz.
With the frequency set to "L", L=3.3 uH.
A frequency of 13 MHz was used because a resonance could not be obtained at
21 MHz. The minimum capacitance in this Q-meter 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 = 3.75, Winding Dia/Shield Dia = 0.65,
inductance ratio = 62%) 3.3/4.7=0.702 (70%)
73 Roger WB0DGF
Telex Communications, Inc. (Hy-Gain)
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