<VV> LM Rear Antenna

[Duane, Jim E.]

Hi all.
I have the raked "AM only" antenna on my '66 vert.  Length of exposed antenna has little effect on the sensitivity of FM.  AM is another matter.  Don't forget to use the AM trim if your radio has it.  Better yet, shut that thing off and listen to the tune of an air cooled flat 6!

Jim Duane
'66 Corsa 180 CVT (radio use optional!)
Colonial Corvairs
CORSA  

-----Original Message-----
From: virtualvairs-bounces at corvair.org [mailto:virtualvairs-bounces at corvair.org] On Behalf Of J R Read_HML
Sent: Wednesday, September 02, 2009 1:31 AM
To: virtualvairs at corvair.org; Dale Dewald
Subject: Re: <VV> LM Rear Antenna

Dale,

Thanks for the cogent reasons WHY the FM antenna should be around 30 inches.

BTW.... how does the speed of light come into play?  What's the formula - if 
you happen to know.

As an aside...  Matt's favorite station is 94.7?  Is that what a 30 inch 
antenna would optimize?

Later, JR


----- Original Message ----- 
From: "Dale Dewald" <dkdewald at pasty.net>
To: <virtualvairs at corvair.org>
Sent: Tuesday, September 01, 2009 8:42 PM
Subject: Re: <VV> LM Rear Antenna


> At 12:00 9/01/2009 -0400, J R Read wrote:
> >>snip<<
>
>>It has something to do with matching the length of the FM signal
>>wave.  Someone into radios can probably explain that.
>
> Most FM broadcast antennas are set up as a 1/4 wave whip.  The length of
> the whip is easily calculated using the desired optimum reception 
> frequency
> and the speed of light (which is also electromagnetic waves).
>
> For the midpoint of the FM broadcast band, 98MHz, the optimum 1/4 wave
> length is 30.1 inches.
>
> For the low end, 88Mhz, use a slightly longer whip: 33.5 inches
> For the high end, 108MHz, use a slightly shorter whip: 27.3 inches.
>
> Most ready made FM antennas I have measured are 31" long.  Adjust your
> telescoping antenna to about 31" or a bit longer if your favorite station
> is in the lower end of the band or a bit shorter if your favorite station
> is in the upper part of the band.
>
>>You can get satisfactory FM reception by using an "AM" collapsible antenna
>>and adjusting it to the FM length.  Now, if you are mounting in the rear,
>>you might be putting a "rake" to it?  I'm not sure how that affects the
>>length requirement.  Some "fine tuning" might be required.
>
> Any rake (15 deg or less) will be insignificant considering the placement
> of the antenna near the rear corner of the car where the ground plane of
> the surrounding car body is asymmetric.  If you really want the best
> reception, place the antenna in the exact center of the roof.
>
> Dale Dewald
> Hancock, MI
>
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