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Close Proximity Air2Air Comm problem (HEL

 
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Fiveonepw(at)aol.com
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PostPosted: Tue Jan 03, 2006 7:24 am    Post subject: Close Proximity Air2Air Comm problem (HEL Reply with quote


Howdy all-
After another frustrating couple of occasions trying to communicate with
fellow formators I MUST come up with some solution to this problem. Recap-
whenever closer than 300' (MOL) to other planes, transmissions from other planes are
typically very garbled & unreadable on my Microair 760. They can hear me
fine & radio works excellent at greater distances. Several listers here have
suggested BNC attenuators to resolve this, but most I've found are limited to
less than the output power of the 760 (about 5watts). See:
http://www.smelectronics.us/bnc,fattenuators.htm
A representative for JFW Industries claims to have a 50 ohm/5 watt unit at a
reasonable price ($45) that he claims will do what I need. Unfortunately, it
seems installing one of these "should" mitigate the formation problem, but
longer-range comm will suffer. I asked about a "switchable" unit. The rep said
it's possible, but much pricier (custom job).
Another A-lister suggested a microwave switch to bypass the attenuator when
not needed.
Bob N. has offered to produce a kit to address the problem, but would have to
order circuit boards and put together parts lists, and could only do so if at
least 4 units were ordered. I haven't heard from anyone else having my
"problem", so that's likely a bust. (Bob- if you see this, is the unit you allude
to similar to the "Active Attenuator for VHF-FM" suggested for fox hunts shown
in the References section of the ARRL handbook? Mine is 78th edition (2001)-
unit is page 30.64) If my understanding of this unit is right, it works by
generating mixing products using an oscillator (requiring tuning reception to
off-frequency? Not sure how this works for transmitting)
Microair tech support suggests the following: "The radio's operation is
normal. What you need is an antenna switch with a lower gain antenna for these
situations. This should reduce the receiver sensitivity at the front end. When
you aren't in formation or in close proximity to other aircraft, you should be
able to switch back to your bent whip for greater sensitivity at the lower
end."
Possible solution: I have a couple of Rubber Duckie antennas. I could mount
one of these to a BNC receptacle on the larger side of a dedicated metal box
(about 3"x3"x1") under my panel with the RD pointed toward the floor. A short
RG400 patch cord from the 760 to the box, and the belly antenna RG400 to
another receptacle on the box. A SPDT switch also mounted to the box would simply
connect either the RD or main antenna to the 760. (Fancier yet, make it a
DPDT feeding a lamp on my annunciator: "AUX ANT ON") If the proximity of the RD
to panel stuff turned out to be a problem, it could be re-located somewhere
aft via a separate RG400, such as under the transverse seat back brace (RV-6A
tip-up).
What say ye wise ones?
Thanks for any suggestions or critique- I have GOTTA fix this!
Mark Phillips - do not archive


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mstewart(at)iss.net
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PostPosted: Tue Jan 03, 2006 7:51 am    Post subject: Close Proximity Air2Air Comm problem (HEL Reply with quote


This is not an unusual problem.
I have it and Id say about 1 in 4 formation guys see this problem in
RV's.
Mike


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sportav8r(at)AOL.COM
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PostPosted: Tue Jan 03, 2006 9:48 am    Post subject: Close Proximity Air2Air Comm problem (HEL Reply with quote


Your annunciator light suggestion triggered an idea: long ago, when dinosaurs, er, when vacuum tube finals ruled the airwaves, we'd dip and load our tube finals into 100w light bulbs used as dummy loads. It was, however, possible to communicate over such an "antenna" at greatly reduced efficiency. And I believe the much lower radiated power output (vs a rubber duck) will reduce the chances that you'll zap sensitive avionics with too much field strength in the cockpit. Maybe try a light bulb in the 50-ohm and 5-10 watt dissipation range as the actual "antenna" for close-in work?


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gmcnutt(at)shaw.ca
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PostPosted: Tue Jan 03, 2006 11:22 am    Post subject: Close Proximity Air2Air Comm problem (HEL Reply with quote


Hi Mark
FWIW, could you hook up and try using a hand-held radio to see how it
would work during formation. If it works OK you might consider a #2
hand-held comm instead of spending $ on the Microair.
George in Langley BC
Fiveonepw(at)aol.com wrote:
Howdy all-
After another frustrating couple of occasions trying to communicate with
fellow formators I MUST come up with some solution to this problem. Recap-
whenever closer than 300' (MOL) to other planes, transmissions from other planes are
typically very garbled & unreadable on my Microair 760.


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BigD(at)DaveMorris.com
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PostPosted: Tue Jan 03, 2006 11:23 am    Post subject: Close Proximity Air2Air Comm problem (HEL Reply with quote

Your idea of having a switchable rubber duckie antenna is probably the best
way to go. Bury the rubber duck somewhere it gets poor reception. An
alternative might be a 50 ohm resistor in whatever power rating your
transmitter is rated, but then you won't get much reception at all, just
your transmitter power will be reduced for the "other" guys'
benefit. Light bulbs used to be popular, but they aren't very reliable and
their resistance might change with heating or cooling.
I would suggest a good quality VHF switch, though, and not just some ole
toggle switch. If you go the cheap route, you mess up the impedance of the
feedlines and you may find yourself not having good communications with the
tower 40 miles out next time you need it.
Take a look at the stuff MFJ Enterprises has. For instance:
http://www.mfjenterprises.com/products.php?prodid=MFJ-1702C
Maybe you could use an RF sensing switch that changes your antenna
automatically between receive and transmit. This one comes to mind,
although it is for switching 2 different radios to the same antenna, so I
don't know if it would work the other way around:
http://www.mfjenterprises.com/products.php?prodid=MFJ-1708
You could try calling MFJ Enterprises, ask to speak to their chief
engineer, and ask them if they have something that would work. Describe
your scenario as a VHF application with radios very close to each other,
but don't mention the AIRxxxxx word.
Regards,
Dave Morris


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brian-yak(at)lloyd.com
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PostPosted: Wed Jan 04, 2006 5:55 pm    Post subject: Close Proximity Air2Air Comm problem (HEL Reply with quote

Fiveonepw(at)aol.com wrote:
Quote:
Microair tech support suggests the following: "The radio's operation is
normal. What you need is an antenna switch with a lower gain antenna for these
situations. This should reduce the receiver sensitivity at the front end. When
you aren't in formation or in close proximity to other aircraft, you should be
able to switch back to your bent whip for greater sensitivity at the lower
end."

Mostly this means that the MicroAir receiver front-end is subject to
front-end overload. I noticed and reported this about 5 years ago. I
find it interesting that they have the problem but others don't.
[quote] Possible solution: I have a couple of Rubber Duckie antennas. I could mount
one of these to a BNC receptacle on the larger side of a dedicated metal box
(about 3"x3"x1") under my panel with the RD pointed toward the floor. A short
RG400 patch cord from the 760 to the box, and the belly antenna RG400 to
another receptacle on the box. A SPDT switch also mounted to the box would simply
connect either the RD or main antenna to the 760. (Fancier yet, make it a
DPDT feeding a lamp on my annunciator: "AUX ANT ON") If the proximity of the RD
to panel stuff turned out to be a problem, it could be re-located somewhere
aft via a separate RG400, such as under the transverse seat back brace (RV-6A
tip-up).


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Fiveonepw(at)aol.com
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PostPosted: Wed Jan 04, 2006 8:15 pm    Post subject: Close Proximity Air2Air Comm problem (HEL Reply with quote


In a message dated 01/04/2006 7:57:59 PM Central Standard Time,
brian-yak(at)lloyd.com writes:
Mostly this means that the MicroAir receiver front-end is subject to
front-end overload. I noticed and reported this about 5 years ago. I
find it interesting that they have the problem but others don't.
Quote:
>

Hi Brian- thanks so much for the reply!
If you've seen Bob N's reply, it appears you two are suggesting the same
thing (drawing came through a bit rough, but appears to be same circuit as Bob
shows- great minds thinking alike and all that...)
Thanks again & welcome back to the States (I guess- sounds like you were
really roughing it last year!)
Mark do not archive


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brian-yak(at)lloyd.com
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PostPosted: Wed Jan 04, 2006 9:17 pm    Post subject: Close Proximity Air2Air Comm problem (HEL Reply with quote


Fiveonepw(at)aol.com wrote:
Quote:
Hi Brian- thanks so much for the reply!

You are welcome.
Quote:
If you've seen Bob N's reply, it appears you two are suggesting the same
thing (drawing came through a bit rough, but appears to be same circuit as Bob
shows- great minds thinking alike and all that...)

Not a lot of magic there. The problem suggested the solution.
Quote:
Thanks again & welcome back to the States (I guess- sounds like you were
really roughing it last year!)

Well, I was living in the US Virgin Islands for three years. I came back
for a job with a start-up in Sacramento after selling my business in the
USVI. Thanks for the welcome back.
Quote:

Mark do not archive

--
Brian Lloyd 2243 Cattle Dr.
brian-yak at lloyd dot com Folsom, CA 95630
+1.916.367.2131 (voice) +1.270.912.0788 (fax)
I fly because it releases my mind from the tyranny of petty things . . .
- Antoine de Saint-Exupery


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