Retractable Comm Antenna

All right, I *know* it's a stupid idea. But it seems like it'd be fun to
build.

I've got a Narco Escort II in my airplane. Like most (all?) Narcos, it
requires separate antennas for the transmit and receive sides. My airplane
has a ~25-year-old coax dipole antenna, and the "CW McCall's Revenge"
antenna I posted about a few years back. See:

http://www.bowersflybaby.com/stories/antenna.htm

I was flying today, and got complaints about the quality of my comm radio
transmissions. Back at the shed, I switched the transmit antenna to the
"McCall's Revenge" side, and a quick test to the Superunicom seemed to
indicate it was back to normal.

The older dipole may be finally giving out...not surprising, since its mate
did, three years back. It seemed to work OK on the receive side, but it's
obvious that I should put either some thought into a new antenna (or a new
radio that needs only one).

I *hate* external antennas. They're ugly. I prefer other options.

Jim Weir sent me some copper tape and some baluns for a new dipole, but I
recently installed a big metal inspection panel in the belly of the beast
(which is where I'd originally planned to mount the dipole) and it's too
tough to get into the tail cone to install it further back.

(Belly panel at: http://www.bowersflybaby.com/tech/belly_pan.html)

I was mulling over the possibilities as I started my car to head home.
Then I noticed the low-pitched buzzing noise: The car radio antenna
extending.

Why not build a retracting comm antenna?

My first thought would be to modify a car unit. Too bulky, too heavy.

My second was to *not* have a "collapsible" type antenna. I considered
just a rod that would slide out a small hole in the belly, but thought that
this would be tough to do with an ordinary whip...I'd need a long bar with
gear teeth to engage the motor.

My final thought was to go with a "hinged" type instead. Have a actuator
that rotates the antenna through 90 degrees... have it parallel to the
belly when the power's off, but rotates to vertical when power is applied.
Like a landing gear.

Anybody got some suggestions for sources for small 90-degree actuators like
this...or any other ideas for retractable antennas?

Ron Wanttaja

Way back in the 1960's when metal gliders flew in contests, an external whip
antenna was considered a lot of unnecessary drag. Several pilots rigged
retractable antennas.

The one I remembered used a curved tube with the whip and coax inside. The
pilot just pushed it out until a stop was reached that allowed just enough
whip exposure for a 1/4 wave at 123.3 MHz. The radios were vacuum tube so
they were only used when they were really needed, otherwise they ran the
batteries down fast.

That description probably left out a lot of important details, but it's all
I remember.

Bill Daniels

"Ron Wanttaja" wrote in message
...
All right, I *know* it's a stupid idea. But it seems like it'd be fun to
build.

I've got a Narco Escort II in my airplane. Like most (all?) Narcos, it
requires separate antennas for the transmit and receive sides. My
airplane
has a ~25-year-old coax dipole antenna, and the "CW McCall's Revenge"
antenna I posted about a few years back. See:

http://www.bowersflybaby.com/stories/antenna.htm

I was flying today, and got complaints about the quality of my comm radio
transmissions. Back at the shed, I switched the transmit antenna to the
"McCall's Revenge" side, and a quick test to the Superunicom seemed to
indicate it was back to normal.

The older dipole may be finally giving out...not surprising, since its
mate
did, three years back. It seemed to work OK on the receive side, but it's
obvious that I should put either some thought into a new antenna (or a new
radio that needs only one).

I *hate* external antennas. They're ugly. I prefer other options.

Jim Weir sent me some copper tape and some baluns for a new dipole, but I
recently installed a big metal inspection panel in the belly of the beast
(which is where I'd originally planned to mount the dipole) and it's too
tough to get into the tail cone to install it further back.

(Belly panel at: http://www.bowersflybaby.com/tech/belly_pan.html)

I was mulling over the possibilities as I started my car to head home.
Then I noticed the low-pitched buzzing noise: The car radio antenna
extending.

Why not build a retracting comm antenna?

My first thought would be to modify a car unit. Too bulky, too heavy.

My second was to *not* have a "collapsible" type antenna. I considered
just a rod that would slide out a small hole in the belly, but thought
that
this would be tough to do with an ordinary whip...I'd need a long bar with
gear teeth to engage the motor.

My final thought was to go with a "hinged" type instead. Have a actuator
that rotates the antenna through 90 degrees... have it parallel to the
belly when the power's off, but rotates to vertical when power is applied.
Like a landing gear.

Anybody got some suggestions for sources for small 90-degree actuators
like
this...or any other ideas for retractable antennas?

Ron Wanttaja

"Ron Wanttaja" wrote in message
...
All right, I *know* it's a stupid idea. But it seems like it'd be fun to
build.

I've got a Narco Escort II in my airplane. Like most (all?) Narcos, it
requires separate antennas for the transmit and receive sides. My
airplane
has a ~25-year-old coax dipole antenna, and the "CW McCall's Revenge"
antenna I posted about a few years back. See:

http://www.bowersflybaby.com/stories/antenna.htm

I was flying today, and got complaints about the quality of my comm radio
transmissions. Back at the shed, I switched the transmit antenna to the
"McCall's Revenge" side, and a quick test to the Superunicom seemed to
indicate it was back to normal.

The older dipole may be finally giving out...not surprising, since its
mate
did, three years back. It seemed to work OK on the receive side, but it's
obvious that I should put either some thought into a new antenna (or a new
radio that needs only one).

I *hate* external antennas. They're ugly. I prefer other options.

Jim Weir sent me some copper tape and some baluns for a new dipole, but I
recently installed a big metal inspection panel in the belly of the beast
(which is where I'd originally planned to mount the dipole) and it's too
tough to get into the tail cone to install it further back.

(Belly panel at: http://www.bowersflybaby.com/tech/belly_pan.html)

I was mulling over the possibilities as I started my car to head home.
Then I noticed the low-pitched buzzing noise: The car radio antenna
extending.

Why not build a retracting comm antenna?

My first thought would be to modify a car unit. Too bulky, too heavy.

My second was to *not* have a "collapsible" type antenna. I considered
just a rod that would slide out a small hole in the belly, but thought
that
this would be tough to do with an ordinary whip...I'd need a long bar with
gear teeth to engage the motor.

My final thought was to go with a "hinged" type instead. Have a actuator
that rotates the antenna through 90 degrees... have it parallel to the
belly when the power's off, but rotates to vertical when power is applied.
Like a landing gear.

Anybody got some suggestions for sources for small 90-degree actuators
like
this...or any other ideas for retractable antennas?

Ron Wanttaja

Why not put the tape on the outside? Put fabric tape over that, file to
fit, paint to match.
Surely you could fish a coax into the tailcone?

Tim Ward

My first thought would be to modify a car unit. Too bulky, too heavy.


G'day Ron,
Have a look at some of the car ones, and the replacement centres. Many of
the ones to suit the Aussie cars have a plastic extension shaft inside that
could be operated like a push pull cable from the cockpit. This would be
very light without the motor and most of the mounting bracket. Now where did
I leave the angle grinder?

You could even have different stops marked for different radio frequency
bands if you wanted to use the one antenna for different bands.

Add it to your checklist, just like flaps, with take off, cruise, pre
aerobatic and landing settings!

Hope this helps,
Peter

On Sun, 5 Sep 2004 19:05:56 -0700, "Tim Ward"
wrote:

Why not put the tape on the outside? Put fabric tape over that, file to
fit, paint to match.
Surely you could fish a coax into the tailcone?

Sure, but "nailing down" the coax along the run is problematic. I don't
want to leave it free to flop around and perhaps snag the elevator walking
beam bellcrank (located behind the pilot seat at the bottom of the
fuselage).

I'd like to get the antenna oriented vertically, too, though for the
receive side, the longitudinal orientation would probably be fine.

Certainly an option, though.


Ron Wanttaja

On Mon, 6 Sep 2004 12:22:58 +1000, "Bushy" wrote:

Have a look at some of the car ones, and the replacement centres. Many of
the ones to suit the Aussie cars have a plastic extension shaft inside that
could be operated like a push pull cable from the cockpit. This would be
very light without the motor and most of the mounting bracket. Now where did
I leave the angle grinder?

You could even have different stops marked for different radio frequency
bands if you wanted to use the one antenna for different bands.

Add it to your checklist, just like flaps, with take off, cruise, pre
aerobatic and landing settings!

I'd have to take a look at one of the automotive ones, as, of course, the
length would have to be changed to match the Comm frequencies and this may
require some really fundamental fiddling with the existing mechanical
aspects.

And I hope to make this fully automatic, like a car antenna. Power-on the
avionics bus, antenna erects. Power-off the bus, antenna stows. I like it
when I don't have to think.

Ron "That's why I've lasted on USENET for twenty years" Wanttaja

Sure, but "nailing down" the coax along the run is problematic.

How about using some polyurethane caulk to use as glue, instead of nailing
it down. A couple of nail straps for the ends to take the strain, then a
few blobs along the way. It is supposed to stay flexible, and is strong as
snot.
--
Jim in NC

On Sun, 5 Sep 2004 23:56:16 -0400, "Morgans"
wrote:


How about using some polyurethane caulk to use as glue, instead of nailing
it down. A couple of nail straps for the ends to take the strain, then a
few blobs along the way. It is supposed to stay flexible, and is strong as
snot.

Access is the problem, not the physical means of attachment. I have to
work through a standard 3 1/2" inspection hole, accessing an area ~24" away
along the same piece of fabric. Imagine wiring your instrument panel by
working through a single instrument hole...that's the kind of access we're
talking about.

Too bad mama's little boy went off to school to be an engineer, and not a
proctologist. :-)

I want to assure folks that I'm not saying it's impossible. I'll find a
way to secure it if I go with the copper-tape in the tailcone, if that
turns out to be the best solution. I'm just exploring the options...one of
which is to pull the Escort and replace it with a modern single-antenna
comm radio. Or add some velcro for a handheld....

Ron Wanttaja

Ron Wanttaja wrote:
...
I'd like to get the antenna oriented vertically, too, though for the
receive side, the longitudinal orientation would probably be fine.


On the Escort II, both nav and comm receive from the nav antenna,
which should be oriented horizontally for more critical nav purposes.
Comm sensitivity is affected, of course, but on my Escort II it
receives comm more than good enough.

Fred F.

Ron Wanttaja wrote in message . ..


Anybody got some suggestions for sources for small 90-degree actuators like
this...or any other ideas for retractable antennas?

Ron Wanttaja

Mid 80's Subarus used a fairly small motor to power their center
headlight retract mechanism. Haven't looked at one in years but as I
recall they were palm sized units.........Surly you could rig
something similar with an electric motor from Tower Hobbies (or even
adapt a servo)an SPDT and a couple of limit switches?
================================
Leon McAtee
Homebuilders required books:

McMaster Carr
Grainger
MSC
Enco
Tower Hobbies
AS+S