Quick Antenna Installation

[Mark Julicher]

I needed to replace a whip antenna with a stick antenna without doing major surgery. Here is a quick photo essay of how I did the job.

Dimensions of the ground plane are 26 inches long by 13 inches wide. Made from .032 aluminum. Once the ground plane is slid in place, the hookup and fasteners are easy. In free air, the SWR is 2.3, but once the ground plane is slid in place between the metal hat stringers and the fabric the SWR dropped to almost perfect. If I did not have metal stringers I would have grounded the ground plane to the fuselage tubing with braided wire and and a radiator clamp to get the same effect.

[Larry Lyons]

Re: Quick Antenna Installation

Nice installation but now a dumb question from a neophite. How much signal/range would you lose if you mounted the antenna upside down so it stuck down in to the fuslage instead of out in to the airstream?
Larry

[TN07]

Re: Quick Antenna Installation

There is another possibility that works quite well with low SWR. Use
Mark's aluminum sheet as a ground plane but mount it on the bottom
of the fuselage. Secure it as required. Use a BNC 3192 double female
bulkhead connector. Same inside attachment of coax and ground plane as Mark's but fasten a "handy-talky" (aircraft band of course) antenna
on the outside. These antennae are sometimes called "rubber duckies".

The antenna will flex with airspeed but works quite well on low speed
aircraft, simply remove it when you are through flying. The only thing visible from the outside of the aircraft with the antenna removed is the through connector.

Bob

[Mark Julicher]

Re: Quick Antenna Installation

TN07, Great idea about the rubber duck antenna. I bet I have 5 of them from old HTs that would work fine. I used to have a bottom mounted VOR antenna at the tail, but tall grass ripped it off. HOWEVER, a rubber duck would be harder to tangle in grass.

Larry, the antenna could be mounted facing internally and it should work OK. There would be some signal loss. Maybe I will have to do a walk around with my signal strength meter one with an innie and once with an outie antenna and compare them. Hmmm. Than might make a great article for a magazine. All I was looking for was a dirt simple antenna mount that did not require me to remove any fabric. My old Wag Aero whip antenna corroded out on the inside and the resulting SWR ruined a handheld.

My only regret now is that my new Icom IC A6 is not supposed to be run while using the DC charging jack for "external power". So I need to come up with another way to get power from my floor mounted gel cell.

There actually are several radio guys lurking here in the tribe, but if we start talking Ham Radio the thread will have to be moved to Rants and Raves.

[Larry Lyons]

Re: Quick Antenna Installation

Well the reason I asked; those of us in the ultra-light world have found sometimes you may suffer a bit of signal loss, but as I do not live in Alaska, but the mid-west I do not worry to much that my radio range going from 25 mi. down to 10 mi. I can not get far enough away to ever worry about reaching an airport from the air. I also, have watched the composite guys go with inside antenna mounts and not lose much range at all, however I am not familiar with the effect that the steel tube construction would have on a radio transmission. So I too am hoping the radio hackers will chime in here. Larry

[Mark Julicher]

Re: Quick Antenna Installation

So I too am hoping the radio hackers will chime in here.....

Well, I definitely qualify as a radio hack. The inside of a fuselage is essentially a Faraday cage but very leaky from an RF standpoint. It is somewhere between voodoo and weird science to predict how the antenna will behave in that complex environment. Antenna experts that figure this stuff out are all identifiable by their huge frontal lobes and their ability to work Smith charts whilst working a crossword puzzle.

All that is to say, I'm sure some signal will get out using an internal antenna, but I can't say how much without collecting empirical evidence.

[Larry Lyons]

Re: Quick Antenna Installation

So I too am hoping the radio hackers will chime in here.....

Well, I definitely qualify as a radio hack. The inside of a fuselage is essentially a Faraday cage but very leaky from an RF standpoint. It is somewhere between voodoo and weird science to predict how the antenna will behave in that complex environment. Antenna experts that figure this stuff out are all identifiable by their huge frontal lobes and their ability to work Smith charts whilst working a crossword puzzle.

All that is to say, I'm sure some signal will get out using an internal antenna, but I can't say how much without collecting empirical evidence.

Sure do not want to hi-jack this thread but I used to have a radio tech that had a screened in porch inside his shop. All brass screen, and he did radio tests in there; either that or it was " ET trying to call home".
Larry

[8708]

Re: Quick Antenna Installation

Hi Mark,
Thanks for the great photos of your grounding plane! That is a neat installation. How did you attach the grounding plane to the stringers and what are the dimensions of the grounding plane?
Thanks!
Jay

[Mark Julicher]

Re: Quick Antenna Installation

Jay,

The ground plane is 13" wide because that is how wide I could make it and still slide it into place without cutting fabric.
The ground plane is 26 inches long because it had to be at least 22 inches long and I had a little extra on my sheet of aluminum.
The ground plane is pointier at one end because my scrap aluminum was narrow at one end. It is not fastened to the stringers at all because the friction fit is superb and it won't move easily as it is. I could have figured out a clamp that would not rub a hole in my fabric, but I did not need it.

So howzat for back of the envelope engineering? My Ham Radio Handbook and a little dumb luck worked OK.