National Aeronca Association Bulletin Board

My order from Aircraft Spruce arrived and now I have 8' of coaxial cable, two BNC connectors (one male one female) and a straight whip antenna (with no connector on it).

I know how to strip the coax and expose the center wire and the wire mesh outer shielding.

So, my question is this: Do I solder the coax center wire directly to the bottom of the whip and then solder the coax shielding to the ground plane? And then put the connector on the other end and hook up to the radio?

Dan,
With the whip strip back the center conductor and install a ring terninal. Connect the shielding to the ground plane with another terminal. You can shove the shielding into the terminal and squeeze it or better yet use a solder-sleeve.
Paul

Paul Agaliotis wrote:Dan,
With the whip strip back the center conductor and install a ring terninal. Connect the shielding to the ground plane with another terminal. You can shove the shielding into the terminal and squeeze it or better yet use a solder-sleeve.
Paul

Thanks, Paul -- I followed all that except a "solder sleeve"?

Copied from the fAA email list. Peter is a engineer with Honeywell aerospace and knows what he is talking about.

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G’Day Dan,

My opinion. And a dozen radio techs will each have their own opinion, so as Tony would say, OMO

1)       You will have a hard time soldering the coax center to the antenna, because of the heat sink effect of the antenna wire. The Delrin insulator should take a fair bit of heat, but I’ll bet the Coax insulator would not. You could destroy it with too much heat. Plus you will curse yourself if you ever have to remove the antenna and have to de-solder it at the flight line. If you are really good with a big old plumbers soldering iron, you could get away with it.

2)       You will not solder to an aluminium ground plane with standard hardware store solder.

So. Two options for the Co-Ax center to the antenna. A) Can you find a slide on terminal of the correct diameter? Your local Radio Shack may have a terminal the correct diameter, in one of those automotive connectors B) Can you thread the exposed end of the antenna below the insulator. Then you could use a regular crimp type eye terminal on the coax center conductor and a pair of nuts to fix the terminal to the antenna.

For the connection to the ground plane, you want the shielded portion of the coax to be as short as possible so as to leave the minimum length of the center conductor un-shielded. I would go for an inch. Put a crimp type eye terminal on the end of the shield and bolt it to the ground plane right next to the base of the antenna. You did remember to drill a clearance hole in the ground planes so the bottom end of the antenna wire does not touch the ground plane didn’t you?

Coax connector on the other end of the cable to mate up to your radio.

Then BEFORE you connect to the radio, use a muiltimeter to check that there is no connection between the coax shield and the coax center conductor. If there is, and you key the transmitter with the antenna connected, you will be buying a new transmitter output stage!

If it is all OK, find a friendly Ham Radio Operator or an aviation radio tech who will check the VSWR for you. And tune the antenna. With that type of wire antenna you should see maybe 1-1/2 to 1 VSWR at 126.9 MHZ and worst case maybe 2.5 to 1 at 118 and 135.9  First time you key it, hit it for no more than a second and check the VSWR. If it doesn’t come up, don’t key it again. If it goes beyond 2-1/2 to 1, don’t key it again. Stop and find out what’s wrong. Something shorted or open? Bad solder joint? Kink the coax that has damaged the center or the shield? I have even had a faulty length of coax, new off the reel with a break in the center conductor.

Seriously, a bad antenna is one thing that can cost you big repair bills. You may want to think about having a radio tech install it for you.

Plus there is the legal side. FCC rules say a licenced guy (or gal. Not being sexist here) must do it.

OR. Pay my airfare and I come visit from Oz and do it for you.

Cheers
Peter Lapthorne

Dan,
A solder-sleeve is a short length of heat shrinkable tubing with a solder ring in the middle. Also inserted is a short length of stranded hook up wire. Once the insulation is stripped from the coax to expose the shielding a solder-sleeve can be installed at the stripped area. A heat gun is used to shrink the sleeve to the coax shielding. At the same time the solder is liquified, connecting the shield to the hook up wire for attaching a ground or anything you want to hook to it.
Paul

Paul Agaliotis wrote:Dan,
A solder-sleeve is a short length of heat shrinkable tubing with a solder ring in the middle. Also inserted is a short length of stranded hook up wire. Once the insulation is stripped from the coax to expose the shielding a solder-sleeve can be installed at the stripped area. A heat gun is used to shrink the sleeve to the coax shielding. At the same time the solder is liquified, connecting the shield to the hook up wire for attaching a ground or anything you want to hook to it.
Paul

Excellent -- thanks!!

OK, had some free time, stopped by Home Depot and replenished my ever-shrinking tool pile (My son builds arrows for his longbow and tools tend to migrate to the shed, never to be seen again )

I've terminated both the center coax wire and the ground shielding with ring crimp-style terminals. I crimped each and then soldered to fill in the gap and ensure security.

I kept the two ends about 1 1/2" apart, and then insulated the whole mess with Liquid Electrical Tape (couldn't find RTV, but this stuff is similar).

I checked continuity -- nothing between ground and hot, so no chance of burning up my Sporty's yet.

I plan on trying the install behind the baggage area first. While there will be some signal loss/ degradation due to the steel tubing back there, I think I should get my threshold 10 mile transmit (I'm sure the whip installed on the wing root is better, but the installation will require drilling an IA approval).

Thanks for the help so far and I'll post the results!

Update:

After a few fits and starts, I have comms!

I had to move the antenna from the rear to the top center of the wing root fairing. This allowed for a much shorter Coax length. I also used a different terminal connector. I checked all continuity several times and all was good.

Last Saturday I took my son up for his first Chief ride and tested the radio -- loud and clear transmissions to tower while 10 miles out, AWOS loud and clear 20 miles out!

All this with a Sporty's handheld I bought in 2002, a straight whip antenna, and some RG-58 coax.

An external antenna makes a hell of a difference, doesn't it. I was astounded at what it did for my old Icom IC A-21.

Roger Anderson wrote:An external antenna makes a hell of a difference, doesn't it. I was astounded at what it did for my old Icom IC A-21.

A properly installed external antenna makes quite a difference -- absolutely!!

Glad to hear that you finally got things sorted out. Being able to communicate, both ways, is a big help.

joea wrote:Glad to hear that you finally got things sorted out. Being able to communicate, both ways, is a big help.

Especially on a Class D, where I was temporarily based. I knew the tower controllers, but some were more accomodating than others.

"If that's Chief 24286 orbiting to the north, cleared to land 18..."

I had the same problem with using a handheld years ago in my Chief. Was very frustrating at times.

joea wrote:I had the same problem with using a handheld years ago in my Chief. Was very frustrating at times.

Yep. While I appreciate the silence and freedom NORDO provides, we fly in crowded skies these days, especially at some airports on a sunny Saturday.