Re: comm's RX antenna

[acepilot]

I assume you are putting an antenna on the OUTSIDE of the van. If this
is the case, there is no such thing as too big a groundplane. If you
are putting the antenna inside, then it is probably more easily
understood that all that metal will be a shield to RF. I would
recommend getting a 1/4 wavelength VHF antenna used for either amateur
radio (144 MHz band) or a commercial highband antenna (150-174 MHz).
You can get ones that require a 3/4" hole in the roof or go with a
magnet mount type. Both antennas mentioned above will be a little short
for airband, but will work infinitely better than an inside antenna of
any kind.

Scott "Ham radio guy" L.



karel adams wrote:
> I want an airband receiver in my car (well, a van actually)
> and wonder what antenna to use best.
> just the normal car antenna perhaps?
> i even wondered about jim weir's J-antenna
> but am afraid the van's body will be too big a grond plane
>
> TIA,
> Karel Adams
>
>

[frank]

karel adams wrote:

>
> "acepilot" > schreef in bericht
> ...
>> I assume you are putting an antenna on the OUTSIDE of the van. If
> this
>> is the case, there is no such thing as too big a groundplane. If you
>> are putting the antenna inside, then it is probably more easily
>> understood that all that metal will be a shield to RF. I would
>> recommend getting a 1/4 wavelength VHF antenna used for either amateur
>> radio (144 MHz band) or a commercial highband antenna (150-174 MHz).
>> You can get ones that require a 3/4" hole in the roof or go with a
>> magnet mount type. Both antennas mentioned above will be a little
> short
>> for airband, but will work infinitely better than an inside antenna of
>> any kind.
>
> Thank you!
> I should have made it clearer
> that I want it outside indeed.
> KA

Why not get a 1/4 wave aviation whip?

[sidk]

Karel, for receiving, a (metal) coathanger will do ok. If you want
something more permanent, "the normal car antenna" is just fine.
However, for transmitting, one must take care to get it right
(impedance match, ground plane, etc...).
BTW, "...too big a grond (sic) plane" is like too much fun.


Sid Knox
Velocity N199RS
Starduster N666SK
KR2 N24TC
W7QJQ


"karel adams" > wrote in message >...
> I want an airband receiver in my car (well, a van actually)
> and wonder what antenna to use best.
> just the normal car antenna perhaps?
> i even wondered about jim weir's J-antenna
> but am afraid the van's body will be too big a grond plane
>
> TIA,
> Karel Adams

[Tim Ward]

"karel adams" > wrote in message
...
> I want an airband receiver in my car (well, a van actually)
> and wonder what antenna to use best.
> just the normal car antenna perhaps?
> i even wondered about jim weir's J-antenna
> but am afraid the van's body will be too big a grond plane
>
> TIA,
> Karel Adams

As someone else pointed out, you can't have too much groundplane.
J-antennas are relatively insensitive to groundplane or lack thereof,
because they're half wave.
The "glider retrieve" crowd tends to like a 5/8 wave whip, which requires a
ground plane and an impedance match, have a narrower bandwidth, and are
taller so they run into more overhanging objects, but puts more of the
signal close to the horizon, so the range is better, ground to ground. (This
is a _retrieve_, remember).
If you can put one of Jim's antennas on your van so that it doesn't whack
too many overhanging things, it should work fine.
I have seen J-poles mounted on bumper hitches and van rear-door hinges, to
keep them a little lower. I doubt if the antenna pattern was precisely
omnidirectional, but the people using them thought they were "good enough".
A quarter-wave whip should also work, and might whack fewer things.

Jim might even agree with this: like airplanes, antenna design is about
compromises.

Tim Ward

[Jim Weir]

If this
->is the case, there is no such thing as too big a groundplane.

Is that a fact? Hm. A quarter wave groundplane is about 4' square (24" in any
direction from the base). Is an 8' square groundplane better? No, as a matter
of fact, an 8' groundplane (half-wave) for the aircraft band will be no ground
plane at all. Same for a full wave. You gotta understand what a "ground plane"
really is.


I would
->recommend getting a 1/4 wavelength VHF antenna used for either amateur
->radio (144 MHz band) or a commercial highband antenna (150-174 MHz).
->You can get ones that require a 3/4" hole in the roof or go with a
->magnet mount type.

Why spend all that money? Why not drill a hole (or make a small metal bracket,
if you don't want to drill holes in a new car) for a BNC (F) UG-1094 connector
and cut a piece of brass brazing rod 22" long. Mount the brazing rod in a BNC
(M) UG-88 connector, fill the connector body with epoxy, and bingo, a ground
plane vertical whip. Bend it back at a 30° angle and it will match 50 ohms a
little better.

Jim
Jim Weir (A&P/IA, CFI, & other good alphabet soup)
VP Eng RST Pres. Cyberchapter EAA Tech. Counselor
http://www.rst-engr.com

[Jay]

The regular car antenna should do fine and save you a bunch of hassel.
I'm not familiar with the anetnna design you're referring too but
there is no such thing as "too big" for a ground plane. You're
approximating infinity (relative to the wavelength of the carrier)
with whatever you use, its just an issue of diminishing returns by
making the ground plane overly large. You're going to have to find an
adapter between the car antenna plug and the BNC or whatever your VHF
comm radio uses. But a linear on that sucker and make friends
everywhere: "Breaker breaker, a big 10-4!, I'm at zero-zero AGL and
making 25kts in a school zone."

Regards



"karel adams" > wrote in message >...
> I want an airband receiver in my car (well, a van actually)
> and wonder what antenna to use best.
> just the normal car antenna perhaps?
> i even wondered about jim weir's J-antenna
> but am afraid the van's body will be too big a grond plane
>
> TIA,
> Karel Adams