[Paddlewise] [Fwd: MORE telescoping whip..VHF]

Here is a second page of thoughts on the topic from my friend.
Hope this is of value. I am going through a vast learning curve
here for myself, so I sincerly appreciate this discussion.

Best regards,

Philip

attached mail follows:

I didn't address a couple points in the original email, so here's another nickel's worth:

1. Wrapping an antenna around the handheld is likely to reduce coverage since the effective antenna length would be small. Not recommended - an antenna has to "grab some air".

2. As to the exact length to cut the wire, there are useful formulas in the Radio Amateur's Handbook or the ARRL Antenna Handbook. My copy is in storage so I can only guess at the formula. Something like: for a quarter-wave:

Length in feet equals 496 divided by the frequency in MegaHertz; 

So let's see, at 174 MHz, a quarter-wave is 34-1/4 inches long. (IF I remembered the correct formula!) Final trimming to length is best done using the VSWR meter and a pair of cutters. Contact your neighborhood ham radio operator. They are usually eager to help.

3. A quarter-wave antenna must have a "counterpoise" of another quarter wavelength. Normally this is provided by the metal in the body of the handy-talky (or the roof of your car etc.). An elevated antenna must provide a counterpoise up there in the air. Hence, the dipole antenna - two quarter-waves, fed from the center conductor and the sheath of the coaxial cable. A ground plane can also be used.

4. At VHF frequencies, a 5/8 wavelength rubber duckie would be pretty long. I've never seen one. At UHF frequencies, they are more feasible because of the shorter wavelength. Non-rubber-duck 5/8 waves are available, but then you'd have to mount them somehow.

5. A more elegant solution would be to use the satellite phone technology that is now coming upon us. Price is probably a barrier right now, though.

6. Talking to Europe on VHF frequencies is next to impossible. I imagine the writer was using the lower-frequency HF bands where "skip" (sky wave) propagation occurs fairly regularly. However, it does illustrate that when atmospheric conditions are right, coverage can be awesome, even with very low power. At VHF and UHF frequencies, coverage is primarily via ground waves, which is basically line-of-sight. Signal cans sometimes be ducted along coastal areas, which usually results in annoying interference from distant stations.

7. Oh yeah, the last and most important topic: SAFETY. Every antenna is also a lightning rod - in the middle of a lake, a very enticing one. Do NOT use an elevated antenna when there is lightning anywhere nearby.


How I do carry on when you hit on "my topic"! See ya bud.

+++++++++++++++++++++++++++++++++
KEN        You are today where your thoughts have brought you; 
                you will be tomorrow where your thoughts take you.
                                                                   ~ James Allen ~


-----Original Message-----
From:	MarcJensen [SMTP:marcjensen_at_earthlink.net]
Sent:	Thursday, March 05, 1998 8:02 AM
To:	PaddleWise_at_lists.intelenet.net
Subject:	Re: [Paddlewise] telescoping  whip..VHF


> A telescoping whip isn't necessairly going to provide a 
> noticible improvement over a rubber duckie. You'd have to 
> set the length using an SWR meter and then it will only be 
> marginally better then a 1/4 wave RD and probably no where 
> as good as a 5/8 duckie.
> 
> BTW, I have talked to Europe using 0.5 watts... but the 
> antenna was 66 feet wide and 88 feet long...

I have access to NiTi super elastic wire (the metal used in the fancy
eye glass frames).  I could make an antenna that would stand up 3 to
4' in length but fold up to a little ball.  You could even wrap it
around the VHF unit.  The question I have is what length would you
make the antenna?  I could potentially make two or three of these
to try out if anyone is interested.  I would need to make the O.D.
more conductive but I have several way of doing that.

Marc.




"If the Women don't find you handsome, they should at least find you 
handy!"
Red Green

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