Homebrew VHF/UHF mobile antenna question
 

Would these work, or am I crazy? I would also entertain the idea of both
being crazy and the ideas working ;-)

Take a normal 146 MHz quarter wave mobile antenna and heat shrink a piece of
insulated wire to it. The wire would be a half wavelength., more or less,
at 446 MHz. Trim the wire for minimum SWR at 446 MHz.

Another idea. Take a 446 MHz quarter wave wire with one end uninsulated.
With the uninsulated end up, attach it to the 146 MHz quarter wave with heat
shrink. Adjust the position and length of the quarter wave wire for minimum
SWR at 446 MHz.

--
Jim
N8EE

to email directly, send to my call sign at arrl dot net

"JLB" wrote in message
.. .
Would these work, or am I crazy? I would also entertain the idea of both
being crazy and the ideas working ;-)

Take a normal 146 MHz quarter wave mobile antenna and heat shrink a piece
of
insulated wire to it. The wire would be a half wavelength., more or less,
at 446 MHz. Trim the wire for minimum SWR at 446 MHz.

Another idea. Take a 446 MHz quarter wave wire with one end uninsulated.
With the uninsulated end up, attach it to the 146 MHz quarter wave with
heat
shrink. Adjust the position and length of the quarter wave wire for
minimum
SWR at 446 MHz.

--
Jim
N8EE

to email directly, send to my call sign at arrl dot net

Idea 1, would probably not work much at 446 as current would have a hard
time to flow into attached insulated wire. general problem with most mobile
antennas is getting enough RF current to flow out into them.

Idea 2, May almost work, as the 446 is almost the third harmonic of 146 and
the antenna would be resonant again, 438 is 3*146 only a 2% change, close
enough to try it once. Bandwidth of antenna is the critical factor, tune
for 3/4 antenna of 446 first and then see where it came out near the 146.
Then split the difference between the two, a sweep of return loss would
show you the antenna bandwidths, and if it is possible, If no go, try Idea
#3

Idea 3, Other cases -- use a dual ban antenna approach, put a loading coil
in the middle (airspace turns), the bottom part is the 446 1/4 wave, and
doesn't "see" the top part due to the coil. Then the full length with
loading coil is equivalent to a loaded 1/4 wave at 146. Start with a 146
and center loading coil to shorten the 146 lengthwise. Then tune the lower
rod for 446, so the coil may not end up in the center, but it will be right
on on both frequencies. (should not take much of a coil since it is only 2%
off) I did a triband one time with two loading coils for Low Band, VHF and
UHF. Had a splitter designed to split off to the three radios in the trunk
too.

Crazy ideas get patented!



"JLB" wrote in message
.. .
Would these work, or am I crazy? I would also entertain the idea of both
being crazy and the ideas working ;-)

Take a normal 146 MHz quarter wave mobile antenna and heat shrink a piece
of
insulated wire to it. The wire would be a half wavelength., more or less,
at 446 MHz. Trim the wire for minimum SWR at 446 MHz.

Another idea. Take a 446 MHz quarter wave wire with one end uninsulated.
With the uninsulated end up, attach it to the 146 MHz quarter wave with
heat
shrink. Adjust the position and length of the quarter wave wire for
minimum
SWR at 446 MHz.

--
Jim
N8EE

to email directly, send to my call sign at arrl dot net

"John Smith" wrote in message
...
Idea 1, would probably not work much at 446 as current would have a hard
time to flow into attached insulated wire. general problem with most
mobile
antennas is getting enough RF current to flow out into them.


There are two ways that Idea 1 can be thought of:

A. The extra wire is a half wave dipole coupled to the 2 meter quarter
wave. By some magic, it resonates and radiates on 446 MHz as a half wave
dipole.

B. A shorted quarter wave transmission line is an open circuit. So is a
half wave open circuit transmission line. The extra wire next to the 2
meter quarter wave acts like an open half wave transmission line,
effectively isolating the upper part of the 2 meter quarter wave when
operating on 446. When the wire is positioned properly, the bottom part of
the 2 meter quarter wave will act like a 446 quarter wave.

Jim
N8EE

to email directly, send to my call sign at arrl dot net

I have the exact antenna described on Idea # 3 ,, I have it on a magnetic
mount, I use it for a bicycle, I have it magnetically mounted on a plate of
steel on the back. I use it for 2m and 70cm, 2m SWR is flat and 70 SWR is
very low, but I also use 156 megs a lot also. I was able to obtain a very
low SWR on all three by folding metal tape in half like a flag at the bottom
of the whip, about 2 inches up. 2 inch tape, tin foil tape for duct work
(not duct tape) it is aluminum foil but about 6 mil and very tacky. I cut it
to achieve a low SWR (about 6 inches length). So its like a metal flag, 2
inch by 6 inch length. Without it, I had very high SWR on the marine band.




"JLB" wrote in message
...


"John Smith" wrote in message
...
Idea 1, would probably not work much at 446 as current would have a hard
time to flow into attached insulated wire. general problem with most
mobile
antennas is getting enough RF current to flow out into them.


There are two ways that Idea 1 can be thought of:

A. The extra wire is a half wave dipole coupled to the 2 meter quarter
wave. By some magic, it resonates and radiates on 446 MHz as a half wave
dipole.

B. A shorted quarter wave transmission line is an open circuit. So is a
half wave open circuit transmission line. The extra wire next to the 2
meter quarter wave acts like an open half wave transmission line,
effectively isolating the upper part of the 2 meter quarter wave when
operating on 446. When the wire is positioned properly, the bottom part
of
the 2 meter quarter wave will act like a 446 quarter wave.

Jim
N8EE

to email directly, send to my call sign at arrl dot net

"JLB" wrote in message
...


"John Smith" wrote in message
...
Idea 1, would probably not work much at 446 as current would have a hard
time to flow into attached insulated wire. general problem with most
mobile
antennas is getting enough RF current to flow out into them.


There are two ways that Idea 1 can be thought of:

A. The extra wire is a half wave dipole coupled to the 2 meter quarter
wave. By some magic, it resonates and radiates on 446 MHz as a half wave
dipole.

It would do that, coupling would be 15 to 20 dB down though, and depends
where it is located too. You could take the same piece and attach it to the
other wire at the base and get the 15 to 20 dB back. (see Idea 1 A
Modified)
You can cut the big rod for 146 and it will also pickup 446 both under 1.5
VSWR (says ) so it is already a great antenna for 446.

Idea1A modified--Just have both rods come up out of the base (attached at
bottom) bent away from each other about 25 degrees or so, one long and one
short. (old time antennas did this one)

B. A shorted quarter wave transmission line is an open circuit. So is a
half wave open circuit transmission line. The extra wire next to the 2
meter quarter wave acts like an open half wave transmission line,
effectively isolating the upper part of the 2 meter quarter wave when
operating on 446. When the wire is positioned properly, the bottom part
of
the 2 meter quarter wave will act like a 446 quarter wave.

It is the amount of coupling between the two upper parts may be low to
lesson the effect. worth testing it, but you would need a different
frequency, as the antenna already picks up both. But the preposed is 446 on
bottom 1/4 resonate, and 1/2wave 446 on top next to rod, and rod could be
at 120 MHz 1/4 wave length. The 1/2 wave may seem like open , but it probly
does not have strong enough coupling onto the 120 Mhz rod to make it look
open. (what if they are attached at that point, like a catus, 1/4 wave 466
up to attach point, 1/2 wave 466, and the rest of the 120 1/4 rod.-another
test? EZNEC! )

Jim
N8EE

to email directly, send to my call sign at arrl dot net