Fig.6. Parts placement on other side.
pot. version can be used with a vernier. You Ci-n make a vernier from the tuning capacitor in the "lunch boxes1' or Lincoln transceivers. Lafayette also has a vernier (69 cents) on page 291 of their *66 catalog- Using most
TVI traceable to 6 meters and channel 2 can be difficult and it takes a little time to get rid of it. Sometimes it is incurable. But, TVI caused by 10 meter radiation interfering with channel 2 is hardly ever difficult to control. A trap known as the half-wave filter is illustrated- The components specified allow its use with transmitters up to approximately 500 watts pep output and the capacitors are most susceptible; especially if vswr is above 1.5:1 ♦ The formula for calculating safe voltage ratings for the capacitors is: C - V"2PxZq where 2P is twice power output and Zq the transmission line impedance.
There are hams who are off the air because of TVI, and it is not necessary since the filter will provide at least 30 db attenuation for the attenuation for the second harmonic and greater attenuation for the third, etc.
verniers will restrict you to 180 degrees rotation, while the pot. will provide 270 degrees. The single pot. is quite adequate for AM work without the vernier; and is considerably cheaper. _K9ALD
C: 100 pf mica or ceramic "dogbone/' 500 v-(up to 500 watt pep). L: 5 turns 3/4" diameter self-supporting coit or tailor-made coil stock- Leave a partial turn for knifing to set desired center frequency with GDO; usually 28.6 inhz. Box: 21y£^x2J4"x5"(moreor less) with center partition. Make a small hole in the center partition for coupling the two sections, but don't use a feed-through by-pass.
Ray Stellhorn, WA0NEA
Official ARRL Bulletin 211
With the coming of the travel season amateurs will be taking advantage of reciprocal operating agreements. Amateurs traveling across the Canadian United States border should apply for an operating permit 30 to 40 days in advance. W/K licensees apply to the PO Dept., Century Bldg., Lisgar St., Ottawa, Canada, or its six regional offices. Canadians apply to the FCC, Washington, D.C 20554. Travelers visiting elsewhere should allow at least two months for processing of requests. Write to ARRL HQ for details on a particular country.
Vernon Fitzpatrick WA80IK McLain Park, M 203 Hancock, Ml 49930
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