Jan 7
Hello Bob,
I am a Houston area based Cubber also. I am based on the west side at Covey Trails. I am rebuilidng a PA 11 and intend to use an ICOM A23 as my main com radio. I am trying maintain a reasonable authentic outside appearance so I share your concerns of range versus outside antennas. This question has been posed here before. I think the best response I have seen was by Lynn Towns in post # 1829 way back in Nov. 2001. He providea a rather lengthy and detailed response explaining his experiences. I have included a partial exert below for your review.
I am an Electrical Engineer but I'm more familiar with digital design than RF transmission. Here are a few thing I know are important.
1. If your going to transmit, it is critical to tune the antenna, cable and transmitter for maximum efficiency. Receiving is much less critical.
2. Cable length is part of the tuning system. Don't just chop a piece of coax plug it in and go transmit without verifying the antenna system is tuned for the installation.
3. Improperly tuned system can damage a transmitter.
4. A folded dipole antenna does not need a ground plane. ( as pionted out in Lynn's text)
5. A "temperary installation " of Duct taping it to the inside of the fuselage fabric keeps the legal issues simple. Velcro may be equally simple.
If you're ever on Houston's west side come by Covey trails. I'm in hangar #49, the southeast corner of the field.
Jeff Fontenot
78629
Exerpt from Lynn Towns' post #1829:
I flew the Champ, and then my PA-11 Cub for
about the last 25 years without any radios. I used earplugs, and I had
a Hush-a-Com intercom.
During the last winter, I started to plan a long cross country with a
friend of mine who also owns a PA-11. He encouraged me to get a radio
so we could communicate on the trip. I didn't immediately agree, but I
finally decided to give it a try.
I bought an ICOM A23 handheld, and I originally tried using it in my
Cub without a headset, and with the rubber ducky antenna. I bought a
RAM adjustable belt clip mount model# RAM-B-149-BC1 to attach the
radio to the windsheild tubing near the throttle ($28.80 from Aircraft
Spruce and Specialty). The mount worked great, but I couldn't hear the
radio at all while I was flying.
Then, I bought a Lightspeed 25XL ANR headset. The ANR curcuit on the
headset emits RF signals that were picked up by the radio antenna,
making reception garbled. My friend said my transmission was fine. I
exchanged the Lightspeed headset for a Pilot Avionics PA 17-79 DNC XL
headset. After posting my problem on a newsgroup, other newsgroup
members responded who had experienced the same problem. Several solved
their problem with the Pilot headset. This system worked OK, but the
range of transmission/reception was limited pretty much to the
pattern; I would estimate 5 miles maximum.
MY PA-11 friend suggested an external antenna. He had been using a 1/4
wave whip antenna mounted on the wing root fairing with his ICOM. I
believe he was getting 25 or 30 mile transmission/reception. I did
some research, and decided the wing root fairing was not an adequate
surface area for a ground plane, making that kind of antenna
inefficient. A folded dipole antenna that does not need a ground plane
seemed like a better choice.
I bought an Advanced Aircraft Electronics VHF-5T folded dipole antenna
(
www.advancedaircraft.com) ($117.95 from Aircraft Spruce and
Specialty) and installed it vertically on the left side of the
fuselage fabric with duct tape. I was able to slide it between the
side fuselage tubing/stringers and the fabric. The bottom end butts
into the lower longeron, the upper end curves inward in the upper
fuselage just below the stringers, and the antenna ends just past the
top center wooden stringer. It is centered fore/aft in the second bay
of the birdcage behind the baggage compartment. My mechanic said it is
not considered a permanent installation, so no 337 is required.
The ICOM radio has a BNC antenna connector like the antenna, so a few
feet of coax finished the installation. There is extremely low loss
without any adapters required using the ICOM handheld (unlike some
handhelds that do not use BNC connectors).
The performance is better than I ever dreamed. I regularly hear
pattern traffic from airports 100 statute miles away, and I once heard
someone that was approximately 200 statute miles away across flat
land. I have transmitted to towers 50 statute miles away, and they
said I was "loud and clear". I really don't know the limits of the
transmission/reception distance, but it is more than adequate.
I'm convinced that this antenna installation is superior to any 1/4
wave ground plane antenna on a fabric covered plane. Besides, it is
inside the fuselage where it doesn't show.
I was very happy with my communications capability, but my handheld
also has a VOR receiver, and that didn't work too well using the
vertical antenna. I reasoned that since the VOR signals are
horizontal, I could add a vee-shaped horizontal antenna to get good
VOR reception. So, I bought another Advanced Aircraft Electronics
antenna and installed it in the birdcage, in a horizontal vee-shape
with the open side facing forward, in the first bay behind the baggage
compartment. I mounted it on the fuselage tubing using balsa wood and
nylon cable ties.
Since the ICOM only has one antenna connector, I wanted a way to
switch between the two antennas. I posted on a newsgroup again, and
got a suggestin from a pilot/ham operator. At his suggestion, I found
and installed a Dow-Key (>.1 db insertion loss) coaxial switch to
easily switch between the two antennas.
The results using the vee-shaped antenna were mixed. Something
(probably the engine/prop) partially blocks the signal from the front,
and the forward VOR reception is only about 20 miles. Anywhere behind
the wings it is 40-50 miles, so it works well going from a VOR, but
not as well going to a VOR. My main purpose in having it was to be
able to duplex to Flight Service Stations, so I can always temporarily
turn if I have to. The VOR also provides a backup for my GPS, but I
have yet to use it for navigation.
Surprisingly however, the horizontal vee antenna works very well as a
communications antenna. Communication range with the vee-shaped
antenna is at least 50 miles. In fact, it works better than the
vertical antenna when communicating with someone directly above or
below me (which often happens in the pattern). If I was going to do it
over again, I would only install the horizontal vee antenna and
eliminate the other antenna and the selector switch.
I eventually bought another Pilot 17-79 headset and a Pilot PA 200-A23
intercom that plugs directly into the ICOM radio (doesn't require a
headset adapter, and comes with a velcro mounted PTT switch). Using
the intercom with matched headsets does not require separate squelch
controls for each headset (this may become a problem with unmatched
headsets). Intercom volume is adjustable separately from the radio
volume.
I am completely satisfied with this system. I think the folded dipole
antenna makes a handheld radio have equivalent performance of just
about any panel-mount radio. And, you can install the entire system
yourself. The only improvement I can even think of would be an
increase of forward VOR range, and I think that would require a VOR
antenna mounted somewhere outside of the fuselage.
Last spring, my PA-11 friend and I took our 73 flight-hour, 16 day
cross-country in our planes (Michigan to southern California, up to
Oregon, and back). It was great fun. My headset was comfortable for
the entire time, and the only problem I had with my radio is that
twice I transmitted too much and the rechargeable battery went dead.
In September, ICOM finally came out with an alkaline battery pack for
the A23. I have had one on order for 2 months, but I still haven't
gotten it.
Now that I have a radio again, I feel safer. I have a better idea who
else is in the pattern, and where they are. It is comforting to know I
can call Flight Service in marginal weather, and the headset makes
flying quieter, more comfortable, and less fatiguing. So far, the
dependability of the radio has been very good. I'm a happy Cub pilot!
Lynn Towns
