On Saturday, December 9, 2017 at 4:00:10 PM UTC-7, Tim Newport-Peace wrote:
At 04:29 09 December 2017, 2G wrote:
On Wednesday, December 6, 2017 at 7:20:30 AM UTC-8, Don Grillo wrote:
I want to purchase an antenna to mount on the top of the ladder on my
RV.=
I've been looking at the RAMI AV-3 and AV-7 antenna's. I will have to
fabr=
icate some sort of rotating base so that I can swing the antenna down
while=
traveling as well as to remove the cable. The RAMI AV-3 has a 27" whip
an=
d needs to be tuned by cutting to length. The AV-7 is 44" in length and
is
=
pre-tuned for freqs 118-137.
=20
Any other cheaper options as these RAMI antenna's are expensive. I will
a=
lso need a cable extension as they only come with 17'.
=20
Anyone with experience in this area and can provide some guidance?=20
=20
I will be using this on a hand held Yeasu FTA-450L com radio.=20
=20
Thanks, Don

https://www.amazon.com/gp/offer-list...lp_new_mbc?ie=
=3DUTF8&condition=3Dnew

The AV-7 is (it says) a 5/8 wave antenna. Taking the mid-band frequency of
127MHz, this equates to a wavelength of 2.24m so 5/8 wavelength is 1.4m,
which is 55 inches. The maximum length of the AV-7 is 44 inches. How does
that work?

For the AV-3, a 1/4 wave antenna, the length would be 22 inches, which is
within the maximum length of the AV-3.

Either a 1/4 wave or 5/8 wave antenna still needs to be a resonant length
for the required frequency for best performance. The only such Airband
antenna that I have ever seen tha did not require tuning was an Array using
rods of different lengths, which is not what the AV-3 or AV-7 are.

Tim Newport-Peace
http://www.newportpeace.co.uk/icom.htm

A 5/8 antenna is typically resonated by adding a base inductor with a tap to match the usual 50-ohm feedline. It's possible to design a nominally 5/8 antenna with a shorter whip and larger inductor, with possibly other matching means to provide a more broadband match.

That's one explanation - another is the specs could be completely made-up!

Mike