Penguin
Too Short a Member
- Joined
- Nov 21, 2009
- Messages
- 1,613
- Location
- Satellite Beach, FL
- Aircraft
- Dominator, 582, 23' Dragon Wings, 60" Warp Drive
- Total Flight Time
- 250+ hours
Let’s see if we can move away from the hating and tackle a winter project that will pay you dividends in the spring – Radio communications.
The Radios
My radio is an Icom A6, typical for low cost ($300) aviation handheld radios. It offers 5 watts PEP, 1.5 watts CW, which is typical for handheld radios. More expensive ($1,200) units offer as much as 8 watts PEP. If you have the money – and the instrument panel real estate – by all means get the larger unit. But don’t expect to be able to talk to Birdy in Australia from your Wauchula, Florida base. VHF is limited to line of sight. This means that your effective range is determined by your altitude – all other things being equal. And that’s what this post is about, making all other things equal.
Most handhelds have exactly the same output power. Many even use the same chip sets for the radio frequency (RF) stages and just offer different packaging and user interfaces. Try them out and see which interfaces are most comfortable to you.
One of the smart things the RF engineers did was to sense how good a match the radiating system (antenna) is at your selected frequency. The worse the match, the lower the power transmitted to protect the delicate final stage. So a poor antenna and coax is a double whammy – it doesn’t radiate effectively and the radio detunes itself in self-preservation.
Making the Rubber Ducky Work
Handhelds typically come with a really nifty flexible antenna commonly referred to as a rubber ducky. These work okay – actually, the crappy side of okay. The problem is that there is very little metal in the breeze and that’s (a part of) what gets the RF job done. The rubber ducky is the transmitting element but it needs a ground plane (counterpoise) to work. The clever RF engineer uses the metal frame of the radio and the battery as the ground plane. Again, not a lot of metal in the breeze. You may have had a friend who replaced their handheld battery and improved performance. Aside from the charge issues, it was likely the improved ground plane that contributed.
I’ve used my handheld with the rubber ducky successfully until recently. Folks I fly with often comment on the “strength” of my signal. One thing that I did to improve performance is to orient the rubber ducky vertically. Aviation antennas are normally vertically polarized (the antenna is oriented up and down). So you are at an immediate disadvantage if your antenna is horizontal. You can pick up a 90* angle BNC connector for a couple of bucks at Radio Shack to help orient your antenna properly. I also replaced the original battery when it died with a lithium-ion unit which seems to hold a charge quite well – usually enough to support 5 or 6 50 minute flights between charges.
<see picture of radio with rubber ducky, horizontally polarized>
![[RotaryForum.com] - Radio Antenna, Mount, and Coax](data:image/gif;base64,R0lGODlhAQABAIAAAAAAAP///yH5BAEAAAAALAAAAAABAAEAAAIBRAA7 "[RotaryForum.com] - Radio Antenna, Mount, and Coax")
<see picture of radio with rubber ducky, vertically polarized>
But, like all gyronauts, I want more POWER. Well, not really more power but better use of my existing power. Hams (amateur radio operators) have a saying – you can’t work them if you can’t hear them. In our context, that means that you could put a massive transmitter on your aircraft, but if you can’t receive the signal, you can’t communicate. So you want an antenna that optimizes your transmit and receive capabilities.
The Dipole Antenna
Antennas often have specifications specified as “dB gain”. This is as measured against a standard – the ¼ wave dipole. I chose the dipole because it is simple, doesn’t require a lot of space, and can be readily assembled at home from pretty common parts. The dipole consists of two elements – a radiating element and a counterpoise. Each is cut to length depending on the desired operating frequency. The aviation band requires a ¼ wave antenna of 20.5” (high end of the band) to 23.75” (low end of the band). I cut mine in the middle of the band (22.5”) as a compromise and because it is pretty close to my base of operation.
I chose to use a counterpoise rather than using the airframe for the antenna ground plane to minimize electrical interference. It also insures a clean RF pattern in all directions. Basically, the dipole pattern is like a really large donut around the radiating element, equal in all horizontal directions. If I used the airframe, the pattern would be biased toward where the most metal is located.
<see pics of dipole>
I chose to mount my dipole on the pitot tube. This location places the antenna as far from the electrically noisy engine as possible. It also gives me a place to mount a yaw indicator. For the mount, I used a section of a scrap 2” square aluminum mast – light, strong, cheap. I used a ¾” stainless steel u-clamp from Lowes to secure the bracket to the pitot tube. The radiating element is attached to a store-bought PL-239 connector – the center connects directly to the radiating element and the exterior to the ground – in this case, the counterpoise. I wanted a low parts count, moisture-resistant installation. And absolutely no bare wires or components hanging out there.
<see bracket details>
I electrically isolated the bracket from the airframe with some duct tape. Yeah, yeah, I know – I’ll improve on this at some future point in my experimentation.
When cutting the counterpoise to length, remember that the bracket is now part of the length of the counterpoise.
Remember to put something on the tip of your antenna to insure no one loses an eye. I have blunt, smallish caps on mine.
The Coax
IMO, the biggest single problem most installations have is using the wrong coax. You need a 50-ohm coax as that is the load the radio is designed to work into. Most BNC-based coax is 75-ohms (e.g., TV cable) and while that will sort of work, it’s far from ideal. Look closely for lettering on the coax – if it has none, it’s neither RG-8 nor RG-58. Use the 50-ohm RG-8 or RG-58 and you’ll see an immediate improvement.
If you’re putting a BNC connector on one end, you are pretty much constrained to RG-58 coax. I got a 6’ length of RG-58 including a BNC on one end and a PL-239 on the other for $8.50 and the owner of the radio shop built it for me while we talked. Apparently he is familiar with my fabrication skills. BTW, never coil the coax and avoid kinking it. I reused my 90* BNC elbow to properly orient my new coax. There are also double-clad 50-ohm coaxes out there which should be great but I’ve never been able to lay my hands on it.
<See picture of typical radio installation>
The Power Source
Returning to the battery for a moment, I use the internal battery on my handheld to isolate it from the engine’s charging system. I may eventually run this from ship power. But if you choose to do so – A WORD OF CAUTION. Most handhelds are not designed to accept 12VDC power. They require an accessory that steps to voltage to the appropriate level. If you don’t use this, YOU WILL FRY YOUR RADIO.
The Microphone
Although I have a pod and windscreen on my Dom, I found myself leaning forward under the windscreen to minimize noise. I solved this problem by using a leather mic cover. My source was Bear Perkins PPC - a vendor I highly recommend.
Radio Horizon
I just ran some numbers for fun. Assuming my local AWOS antenna is at 30 ft., its radio horizon is 8 miles.
Assuming I'm flying at 500 ft. (I would NEVER fly lower than that ...), my radio horizon is 38 miles.
This is in the terrain-free Florida world, of course.
Now go enjoy your new system. I can trigger the AWOS from 8 miles at 500 feet and can not only key it, but can pretty clearly copy the AWOS transmission. This is about a 4:1 improvement over my rubber ducky. I don’t use any ferrite beads, chokes, do-dads, or jim-cracks on mine. Your mileage may vary.
What’s next for me? I’m putting a strobe aboard and can’t wait to see what that does to RF noise. Better electrical isolaiton. Then try usng the airframe as a ground plane. Maybe a gain-type antenna. And ship’s power. There's always something.
The Radios
My radio is an Icom A6, typical for low cost ($300) aviation handheld radios. It offers 5 watts PEP, 1.5 watts CW, which is typical for handheld radios. More expensive ($1,200) units offer as much as 8 watts PEP. If you have the money – and the instrument panel real estate – by all means get the larger unit. But don’t expect to be able to talk to Birdy in Australia from your Wauchula, Florida base. VHF is limited to line of sight. This means that your effective range is determined by your altitude – all other things being equal. And that’s what this post is about, making all other things equal.
Most handhelds have exactly the same output power. Many even use the same chip sets for the radio frequency (RF) stages and just offer different packaging and user interfaces. Try them out and see which interfaces are most comfortable to you.
One of the smart things the RF engineers did was to sense how good a match the radiating system (antenna) is at your selected frequency. The worse the match, the lower the power transmitted to protect the delicate final stage. So a poor antenna and coax is a double whammy – it doesn’t radiate effectively and the radio detunes itself in self-preservation.
Making the Rubber Ducky Work
Handhelds typically come with a really nifty flexible antenna commonly referred to as a rubber ducky. These work okay – actually, the crappy side of okay. The problem is that there is very little metal in the breeze and that’s (a part of) what gets the RF job done. The rubber ducky is the transmitting element but it needs a ground plane (counterpoise) to work. The clever RF engineer uses the metal frame of the radio and the battery as the ground plane. Again, not a lot of metal in the breeze. You may have had a friend who replaced their handheld battery and improved performance. Aside from the charge issues, it was likely the improved ground plane that contributed.
I’ve used my handheld with the rubber ducky successfully until recently. Folks I fly with often comment on the “strength” of my signal. One thing that I did to improve performance is to orient the rubber ducky vertically. Aviation antennas are normally vertically polarized (the antenna is oriented up and down). So you are at an immediate disadvantage if your antenna is horizontal. You can pick up a 90* angle BNC connector for a couple of bucks at Radio Shack to help orient your antenna properly. I also replaced the original battery when it died with a lithium-ion unit which seems to hold a charge quite well – usually enough to support 5 or 6 50 minute flights between charges.
<see picture of radio with rubber ducky, horizontally polarized>
<see picture of radio with rubber ducky, vertically polarized>
But, like all gyronauts, I want more POWER. Well, not really more power but better use of my existing power. Hams (amateur radio operators) have a saying – you can’t work them if you can’t hear them. In our context, that means that you could put a massive transmitter on your aircraft, but if you can’t receive the signal, you can’t communicate. So you want an antenna that optimizes your transmit and receive capabilities.
The Dipole Antenna
Antennas often have specifications specified as “dB gain”. This is as measured against a standard – the ¼ wave dipole. I chose the dipole because it is simple, doesn’t require a lot of space, and can be readily assembled at home from pretty common parts. The dipole consists of two elements – a radiating element and a counterpoise. Each is cut to length depending on the desired operating frequency. The aviation band requires a ¼ wave antenna of 20.5” (high end of the band) to 23.75” (low end of the band). I cut mine in the middle of the band (22.5”) as a compromise and because it is pretty close to my base of operation.
I chose to use a counterpoise rather than using the airframe for the antenna ground plane to minimize electrical interference. It also insures a clean RF pattern in all directions. Basically, the dipole pattern is like a really large donut around the radiating element, equal in all horizontal directions. If I used the airframe, the pattern would be biased toward where the most metal is located.
<see pics of dipole>
I chose to mount my dipole on the pitot tube. This location places the antenna as far from the electrically noisy engine as possible. It also gives me a place to mount a yaw indicator. For the mount, I used a section of a scrap 2” square aluminum mast – light, strong, cheap. I used a ¾” stainless steel u-clamp from Lowes to secure the bracket to the pitot tube. The radiating element is attached to a store-bought PL-239 connector – the center connects directly to the radiating element and the exterior to the ground – in this case, the counterpoise. I wanted a low parts count, moisture-resistant installation. And absolutely no bare wires or components hanging out there.
<see bracket details>
I electrically isolated the bracket from the airframe with some duct tape. Yeah, yeah, I know – I’ll improve on this at some future point in my experimentation.
When cutting the counterpoise to length, remember that the bracket is now part of the length of the counterpoise.
Remember to put something on the tip of your antenna to insure no one loses an eye. I have blunt, smallish caps on mine.
The Coax
IMO, the biggest single problem most installations have is using the wrong coax. You need a 50-ohm coax as that is the load the radio is designed to work into. Most BNC-based coax is 75-ohms (e.g., TV cable) and while that will sort of work, it’s far from ideal. Look closely for lettering on the coax – if it has none, it’s neither RG-8 nor RG-58. Use the 50-ohm RG-8 or RG-58 and you’ll see an immediate improvement.
If you’re putting a BNC connector on one end, you are pretty much constrained to RG-58 coax. I got a 6’ length of RG-58 including a BNC on one end and a PL-239 on the other for $8.50 and the owner of the radio shop built it for me while we talked. Apparently he is familiar with my fabrication skills. BTW, never coil the coax and avoid kinking it. I reused my 90* BNC elbow to properly orient my new coax. There are also double-clad 50-ohm coaxes out there which should be great but I’ve never been able to lay my hands on it.
<See picture of typical radio installation>
The Power Source
Returning to the battery for a moment, I use the internal battery on my handheld to isolate it from the engine’s charging system. I may eventually run this from ship power. But if you choose to do so – A WORD OF CAUTION. Most handhelds are not designed to accept 12VDC power. They require an accessory that steps to voltage to the appropriate level. If you don’t use this, YOU WILL FRY YOUR RADIO.
The Microphone
Although I have a pod and windscreen on my Dom, I found myself leaning forward under the windscreen to minimize noise. I solved this problem by using a leather mic cover. My source was Bear Perkins PPC - a vendor I highly recommend.
Radio Horizon
I just ran some numbers for fun. Assuming my local AWOS antenna is at 30 ft., its radio horizon is 8 miles.
Assuming I'm flying at 500 ft. (I would NEVER fly lower than that ...), my radio horizon is 38 miles.
This is in the terrain-free Florida world, of course.
Now go enjoy your new system. I can trigger the AWOS from 8 miles at 500 feet and can not only key it, but can pretty clearly copy the AWOS transmission. This is about a 4:1 improvement over my rubber ducky. I don’t use any ferrite beads, chokes, do-dads, or jim-cracks on mine. Your mileage may vary.
What’s next for me? I’m putting a strobe aboard and can’t wait to see what that does to RF noise. Better electrical isolaiton. Then try usng the airframe as a ground plane. Maybe a gain-type antenna. And ship’s power. There's always something.
Last edited:
![[RotaryForum.com] - Radio Antenna, Mount, and Coax](https://data3.rotaryforum.com/attachments/88/88152-04b450a136035059dbb4b4f9b87145cf.jpg?hash=KRBpqQ8N_B)
