Antennas

[Rasool]

I have an Icom A6 radio and need to purchase and install an antenna on my Dominator single. Does anyone fly a Dominator single with a dipole antenna? If so, how and where did you mount it. I think I could mount a dipole effectively on the main landing gear strut, but it would look goofy, to be honest. And since I am only doing local flying, I don't think I need the (supposed) increased range of a dipole antenna. I am leaning towards a 1/4 wave whip antenna which I could mount above or below on the forward pod. This would, frankly, look much better, and probably work just fine for my needs. Please respond with any thoughts, opinions, photos, etc.

Thanks,

Russ

 

[eddie]

You might want to just try the radio with the antenna on it,I have a friend who flys with just the normal antenna on his A6 and he has good reception.

 

[Rasool]

Eddie, that was my original intent. But I bought a Flycom helmet and found that although I could hear others on the radio just fine, I could not communicate back with them. After further investigation and consultation with Flycom, they determined that I was getting feedback from the radio antenna. They duplicated the problem in their labs and found that the problem was resolved with an external antenna.

 

[eddie]

Who would have thought that ?

 

[Rasool]

I know, right? But it is a great helmet, and not inexpensive. So a remote antenna is the plan.

 

[Gyro28866]

Rasool:
I mounted a piece of flat stock below the pod using the two rear pod mounting bolts. It was approx. 8" long and 3" wide. I created a radius bend in the sheet stock and mounted it with the radius in front of the bolts. The antenna is attached to he sheet stock with an NMO mount. This gives the antenna a bit of a spring action and the element is still vertical, pointing down from the keel. I did not like the SWR at 2+/1; so I cut and bent another sheet of stock and slipped it between the pod and keel. This extra piece created a counterpoise (ground plain) for the radiating element. The SWR is 1.1/1 and I like that. Also note: the radiating element will require being trimmed to length for the bandwidth you wish to use.
Following is a post in another thread that I posted recently:

A quarter-wave antenna is theoretically 36 ohms since it's half of a dipole antenna which is 72 ohms. The dipole antenna needs no ground plane but can you imagine a 46" antenna sticking up somewhere on the outside of our gyro's. On a dipole, the shield of the coax feeds one half of the antenna while the center wire of the coax feeds the other half. In a quarter-wave antenna installation, the coax's center wire feeds the insulated antenna element while the shield "feeds" the ground or is grounded to the metal structure. The metal material around the antenna becomes the other half of the antenna system. Even though this is not a di-pole in the purest sence, electrically it is still a di-pole, being that the aircraft structure becomes the ground plane. The formula for figuring a half wavelength is: 492 / freq(in MHz) x 12 to give the length in inches. So to figure a quarter wavelength, the formula would be: 246 / freq(MHz) x 12. However, those figures are generally for frequencies below 30 MHz or so (shortwave bands). It's been found that as your frequency increases above 30 MHz, the ends of the antenna begin to affect the real world length and calculations need to be adjusted dowm about 5%. So we use a slightly different formula: 236/freq (MHz) for antenna lengths at our operating frequencies for real world applications. Example: find a quarter-wave antenna length for a 121 MHz operating frequency. (236/121x12) 236 / 121 = 1.95' x 12" = 23.4" for the rod. The ground plane radials should be 5% more or about 24.6". If they are longer, it's not a problem. If, for example, you use 118.0 MHz for the lower end of your "operating range of channels" and 126 MHz for the upper end, you'll find that the center frequency will be 122 MHz. Therefore if you cut your antenna for 122 MHz it will be the most efficient at that frequency with a slight loss at 118 and 126. This loss will only be measurable with an SWR tester. The lengths for those two frequencies will be approximately 23.8" for 118 MHz and approximately 22.3" for 126 MHz. So we have a difference of 1.5" over that 8 MHz channel spread. This is why we say the length is nothing to get really concerned about. In our 121 MHz example, a half inch either way from the 23.4" calculation will work just fine. Of course, there comes a point where the SWR is a problem, I personally trimmed my radiator (antenna element) to be resonant at 122.8 combined with an attached ground plane in base of my pod. This gives me the best SWR of 1.1to 1; the farther off frequency you go the greater the SWR. But, at the extremes of our range, I still only see about 2 to 1. Please note, the higher the SWR the less efficient the transmitting system becomes and will cause internal damage to your radio. The ground plane, or counterpoise as it's actually called, is at the base or feedpoint (where the coax is connected) to the antenna. Ideally, the ground plane would be a disc with a radius of 5% or more than the active (vertical) element or, in our example of 23", about 24-1/4". However, on our gyros, it is not practical. We can use 4 wires or rods in place of the disc with excellent results but again, depending on the aircraft/application, it may not be practical. In my particular application on my Dominator gyro. I utilize a piece of metal sheeting and basically lined the bottom of the pod, passing across between the keel and pod.

 

[EI-BENSEN]

David,
Hi, would you have a photo of your antenna set up on your Dominator.
Paddy

 

[Rasool]

This sounds like an excellent solution. I agree that a picture would be very helpful. Thanks!
Russ

 

[eddie]

Russ on the internet type in ( a high performance half wave dipole antenna) there you will find a how to build a quarter wave antenna.

I used solid core house electrical wire to build my antenna,but it was mounted inside and out of the wind,I suppose gas welding rod rod would work just fine.

 

[Rasool]

Thank you Eddie. The article by Dean A. Scott provides very detailed and clear instructions (with photos) on how to build an inverted "V" halfwave dipole antenna. This is one more excellent option for a very good remote antenna for my Dominator. To be honest though, this may be more antenna than I really need, since my flying is going to be very local around my home airport.

 

[gyromike]

You can try adding a "tiger tail" to you handheld radio to see if that improves performance. It just a piece of insulated wire cut to the frequency you want, and placed under your BNC connector, or SMA, or whatever your radio uses.
Your hand and body actually complete the other half of the antenna when you hold it, but if mounted remotely the other half of antenna, called the 'counterpoise', is now missing.
Simple to make.

 

[harry56]

thanks

สมครบาคารา

 

[EI-BENSEN]

David,
Did you ever get that photo of your antenna.
Paddy

 

[CGS Hawker]

No Title

I made 2 of these. One for me on my CGS Hawk Ultralight and one for my brother on his Gyrobee Ultralight. Work very well!
Made one out of very thin rod and other (mine) out of coat hanger!!!


http://chrusion.com/BJ7/InvVeeAntenna4ULs_rev3.pdf