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Author Topic: K40 for 6m  (Read 617 times)
KB3GUN
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« on: August 25, 2001, 01:02:33 AM »

Can I convert a K40 to use for 6m mobile operation? I'm out of town without my books to figure it out for myself.
If so, what's the suggested length for the steel whip?

I'm running an Icom-706.

Thanks!
KB3GUN
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KE4SKY
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« Reply #1 on: August 27, 2001, 03:17:35 PM »

Easiest and least fuss mobile antenna for 6 meter FM is ANY 2-meter 5/8 wave whip.  If the antenna has a decent VSWR on 2 meters, say no worse than 1.5:1 over the 2-meter FM from 145-147.9 MHz, it in all likelihood will be acceptable at the 6-meter FM range from 52-53 Mhz.

I have used a variety of 2-meter 5/8 wave mobile whips on 6 meters and currently run my RCA Tac-Tec and two meter rig together on a duplexer.  This actually results in better isolation than trying to have separate 2m and 6m antennas on the vehicle.  I used to have trouble with the 100w 6m rig activating the protection circuit on my 2 meter mobile amp when I ran separate antennas, because the 2 meter antenna was loading up whenever I transmitted on six.  On the air comparisons working E-skip from the Washington, DC area into Ontario didn't show a significant difference between an SF-2 Hustler 2-meter whip and a 6 m hamstick.  Your mileage may vary, but it works for me!
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WB2WIK
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« Reply #2 on: August 27, 2001, 06:04:05 PM »

I think the K40 is a CB antenna, a base-loaded whip.  If so, I doubt it could work on 6m at all, cut to any length, because there's too much inductance in the base coil...you might have to cut the whip all the way down to nothing!

Without knowing exactly HOW much inductance is in that base loading coil, it's impossible to predict what, if any, whip length would resonate the antenna on 6m.  If you don't mind sacrificing the antenna, anyway, you might try an Antenna Analyzer like the MFJ-259...and start cutting the whip down, to see how many MHz per inch you get.  That is to say, if you cut an inch off the whip and its resonant frequency changes from 27 MHz to 29 MHz, that's 2 MHz per inch.  At 2 MHz/in, you'd need to cut 12.5" off the whip to tune it down to 52 MHz.  Something like that...you'll find out, if you start doing it!

73 de Steve WB2WIK/6
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