Radio Issues

[PPG Doug]

I am one of many having issues when I transmit using my Icom A6 radio. I am considering a couple of possible fixes and would like some feedback. Icom says not to use anything other than their Icom whip antenna. My question is:

Can I use coaxial cable such as RG-50 and mount my standard Icom whip antenna elsewhere on the gyro for better reception?
Are there any longer antennas I can use on this handheld without causing problems like Icom implies?


One FIX I found on-line a guy posted the following:

The final fix that has been working flawlessly to date is to install the Ferrite bead (RF choke) that was installed on the charger cable, and install it on the coax itself about two inches behind the BNC coax connector to the IC-A6.

My plan is to mount my handheld horizontally so I can read the face etc. and then use a 90 degree BNC connector to then run a whip antenna vertically downward (such as this: http://www.bellnw.com/products/0710/index.htm ) , OR, do the same, but run 6-10' of RG-50/58? cable and reattach the Icom whip antenna to IT, but mount the antenna elsewhere for better TX ability.

Any nice suggestions on how to mount that Icom whip antenna? Brackets etc...

Any thoughts?

Thanks!

[brs]

Doug,
The problem with taking a whip or handheld rubber ducky and extending it with a piece of coax is that the whip is only half the antenna. The radio becomes the other half or counterpoise. You have stated that your problem is during transmit but you did not explain what the problem is (noise, weak audio, weak signal, etc) so I'll give a few general ideas of what can be done.

First off you really need an SWR meter for what I'm going to tell you and you need to know how to use it but hey you might get lucky without it. I'll touch on a bit of antenna theory. Your basic antenna is a dipole (two whips) of a 1/4 wave length each or a 1/2 wave in total. One whip is connected to the center of the coax and the other to the ground of the coax right where the center is taken out of the shield. The formula to determine a 1/4 wave is 234 / freq in Mhz = lenght in feet. See this website http://www.qsl.net/kb5wck/antenna.html . So 234/119.00=1.97 feet or about 23.5 inches. Also, you must mount your antenna away from any other metal or wire. Preferably more than a 1/4 wave length.

On my Sportcopter all I used for an antenna was a length of coax with 23.5" of the insulation removed and then the center carefully pulled through the braid at the same point. I stretched out the center from the braid end to end to make a 46" antenna then mounted it vertically on the enclosure with the feed end of the coax coming out at a right angle. I do have a nice SWR meter and was able to trim the ends of the antenna to get a near perfect 1:1 match. Now I know your enclosure does not have that long vertical side like the Vortex does so here is another solution.

Get an 1/8" brass welding rod. Start with about 25" or longer. Mount it to your enclosure vertically so that it is away from all metal except the lower end. Mount the lower end very close to a bolt on your airframe. Run your coax to the bottom of the antenna near the airframe. Solder the center of the coax to the welding rod and attach the braid to a bolt on the airframe. Make sure your connections are solid and that the coax attach point and antenna are not free to move about at all. Run the other end of the coax to your radio. You will have to tune by trimming the top of the welding rod for a good SWR. Since I doubt you have a meter just trim it so that the distance from where the center of the coax leaves the braid to the top of the antenna is about 23.5".

In general most hand held radios will just reduce the power output in the presence of an high SWR (poor antenna) to protect themselves. Also, your rubber-ducky antenna, in case you are wondering, is a 1/4 wave electrically but not physically. That's why it is coiled and likely has a small capacitor hidden inside.

Good luck.

[Timchick]

I had my Icom mounted on top of my thigh with the whip antenna. Every time I tried to transmit it would squeal. We finally figured out the antenna being too close to my helmet mic was causing the problem. I extended my whip antenna out to the front of my instrument pod with a 6' piece of coax with BNC connectors on each end. I purchased it at Radio Shack. Problem solved. I could hear others and they could hear me.

[PPG Doug]

OK. My plan was to copy Scott Bisers' set up. But, his antenna is homemade by a friend of his. I'm trying to arrange a 90 degree antenna attachment (via Radio Shack) and then reattach my rubber-ducky antenna. But, I was hoping to lengthen the antenna while I was at it.

Yes Tim, my issue was very poor transmitting. I have been wearing my radio on my left shoulder strap. Thus, the antenna was very, very close to my Comtronics mic. So, this new radio mount should solve that part by moving the radio away from me. I was just trying to further improve on my transmitting abilities with a better antenna etc.

I remember seeing your post Tim about placing your antenna out front via coaxial cable.


Exactly what cable did you use? RG-50, RG-58...?

How did you mount your rubber Icom antenna? Vertically?

If so, did you find an off the shelf little bracket or create one yourself?

I had read elsewhere about the proper length of an antenna being approximately 23" or so, which is what BRS was referring to I believe.

Thanks a bunch for the help fellas.

[Resasi]

I tuck my Icom A-6 into the front of my jacket ( Winter mode. Summer mode flying suit has a chest pocket which is handy.) My reception is generally OK but transmission is variable.

Week before last all transmissions were 5x5 but I have previously been reported as being almost completely unreadable??

On the Hornet we have put a whip antenna projecting down from the keel and will try to connect from our radio mount via some coax and the BNC connectors. Might try this ferrite bead choke as well and see how that does.

[edypaul]

Comtronics has a problem with the A6 adapter cable. If you call them they will tell you that. An external antenna helps some.

[PPG Doug]

How about a Ferrite Choke? Anyone try one with success?

If so, where did you place it in the system?

Radio - Antenna - PTT cord - Helmet cord...?

[jcarleto]

I used one of those 90 degree BNC adaptors for a while. It worked well until it fell off. Somewhere in a field in NW Georgia there is a pretty good little duckie antenna with a nice 90 degree adaptor on it. If you use one, make checking the tightness part of the pre-flight.

If you extend the antenna, make sure you get RG-58. Radio Shack also sells RG-59 with BNC connectors that is not appropriate for aircraft radio antenna use.

[PPG Doug]

Thanks. I wasn't sure which RG cable to use.

[Chuck Roberg]

Thanks. I wasn't sure which RG cable to use.

RG-58 is 50 ohm.

RG-59 is 75 ohm. Same as what you would use for a TV antenna.

[PPG Doug]

And I need 50 ohm then? Thanks. I don't know why, but as long as I know which...

Thanks!

[Resasi]

Oops!!!

Before we knew that RG-58/50hm cable was the cable to use we had obtained some coaxial from Radio Shack??? and ran it from the radio mount to the antenna.

Is there some way of ascertaining what type of cable we have put in?
(ie lucked out and got the correct one? Sods Law states the probability of this being the case is 100 to 1 against.):puke:

[PPG Doug]

Man this RF stuff, Ferrite Chokes, which Ohm cable to use, length and type of antenna, electret mics, blah blah blah is crazy voodoo to me. The more I read, the more I get confused.

But, the more I Google, the more I find that I am not alone in searching for The Way to get rid of RF with a handheld and to improve its transmission quality & distance. Strange that Icom doesn't tell you what grief lays ahead when you try to actually use their radio in flight!

[HobbyCAD]

Doug, I'll write up a post tonight, on how to set up things. It's no black art, it's simply something that is not done every day, so usually people don't know much about it.

For a start, reading your last post, you want to maximize the Radio Frequency (RF) transfer, by optimising the connector and co-axial cable choice, and making up a proper cable, and correctly position the antenna. Then you want to minimize the Electromagnetic Interference (EMI), by putting on an RF Choke, or a Ferrite Bead, on affected leads, or repositioning items to not induce the EMI into your radio system.

I'm off to work now, more on the topic later.

Francois

[fiveboy]

Doug

I posted about a similar situation a while back that got cleared up very elegantly using a new type of antenna.

http://www.rotaryforum.com/forum/showthread.php?t=18732&highlight=miracle+whip

[PPG Doug]

FIVEBOY,

What radio are you using this with? I have the Icom A6.

Also, is this the right antenna?


http://www.miracleantenna.com/AirWhip.htm


Thanks.

[getut]

Doug,

I had an A6 and had troubles with it. One of my transmission troubles is that on the A6 if you use the PTT on the radio itself it will activate BOTH the in-radio microphone as well as any headset mic at the same time. You will get horrible wind and engine noise and a squeal on the receiving end. Almost all of what I thought was squeal or interference or antenna problems was simply due to all the wind and engine noise being picked up.

You MUST use an external PTT switch to activate only the headset microphone with that handset. Looking at the pictures in that one post it is hard to tell if you have an external PTT switch.

[fiveboy]

Doug that is the precise antenna I installed. No ground planes, no cutting, no math. I posted pictures of the install

You dont want to use the duckie its strictly low end.

Call the manufacturer - I did and they are super helpful and knowledgeable. They wont even take the order they refer you to Spruce.

[Timchick]

Doug, I can't remember if I used RG58 or RG59. Both are available at Radio Shack. I also used an external PTT switch. I tie wrapped the coax to the instrument pod aluminum mount and just tie wrapped the whip antenna to the mount up at the front. It stuck out at about a 45 degree angle sticking out in front of my pod. I'm not claiming it was the perfect way or the correct way of mounting an antenna but it worked for me. I wasn't trying to talk to ATC, just the guys I was flying with.

[PPG Doug]

Good info. Thanks fellas.

[brs]

Doug,
Since you seem to be going extended hand held antenna route I'll pipe-in again. The choke idea is a sound practice especially with what you are planning. I don't know much about using a ferrite choke as pictured in a previous post as the material it is made of is important for the frequencies you are using. One technique that I have seen is to use a 1/4 wave (23.5" in your case) and make a single horizontal loop just below your antenna.

I'll explain, forgive me if I get too detailed. Radio frequencies are not like DC battery currents. They can be sorted out without even touching the antenna. When you have a poorly matched antenna it creates reflected radio energy on the shield which goes back to the radio. As a result the radio throttles back on it's transmit power. By using the right ferrite choke or coax choke (as above) you shunt the reflected power so it does not go back and interfere with the radio.

Yes RG58 is 50 Ohm which is what you want to use. Look at your radio specifications and it will likely tell you that your anteanna is 52 (same thing) ohm. Remember to keep the antenna clear from other metalic items. Hope you can post a photo when you get it set up.

[WHY]

Hi Doug

A little side note, I buy a ot of stuff from R Shack, but the last time I bought any coax cable from them it was really low end stuff, looked like it only used about 70 to 75 percent braid shield. You might get away with the open shielding but at these frequencies I prefer 90 percent plus shielding (Belden is a good brand). If you have any problems , you might suspect the shielding.

Tony

[Resasi]

Where does one get a ferrite coax or antenna choke?

Are they different?

Are there specific chokes for specific radios?

Thanks.

[PPG Doug]

Doug,
Get an 1/8" brass welding rod. Start with about 25" or longer. Mount it to your enclosure vertically so that it is away from all metal except the lower end. Mount the lower end very close to a bolt on your airframe. Run your coax to the bottom of the antenna near the airframe. Solder the center of the coax to the welding rod and attach the braid to a bolt on the airframe. Make sure your connections are solid and that the coax attach point and antenna are not free to move about at all. Run the other end of the coax to your radio. You will have to tune by trimming the top of the welding rod for a good SWR. Since I doubt you have a meter just trim it so that the distance from where the center of the coax leaves the braid to the top of the antenna is about 23.5".

Good luck.


Thanks. I have a call into my buddy Scott, who's radio is pictured below. His antenna is homemade by a friend of his. I'm not sure how they made it, but is sounds a bit like you suggested above.

Any pictures you could add would be great as RF and antennas are NOT my area...

[PPG Doug]

Doug,
You MUST use an external PTT switch to activate only the headset microphone with that handset. Looking at the pictures in that one post it is hard to tell if you have an external PTT switch.

Thos pictures are of my buddies' gyro, not mine. I do use a PTT button mounted on my control stick.

Keep the suggestions coming...

[PPG Doug]

Hi Doug

A little side note, I buy a ot of stuff from R Shack, but the last time I bought any coax cable from them it was really low end stuff, looked like it only used about 70 to 75 percent braid shield. You might get away with the open shielding but at these frequencies I prefer 90 percent plus shielding (Belden is a good brand). If you have any problems , you might suspect the shielding.

Tony

That is good to know. I was leaning towards them as I found a 2' piece of RG-58. One guy rated it on their site and hated it. I guess he agrees with you. But, such a short piece of RG-58 isn't easy to find...

http://www.radioshack.com/product/index.jsp?productId=2102420


Any suggestions on where to find a 2-3' piece of good shielded RG-58 coax? Again, the short length is the hard part from what I can see. It would seem that whatever ends are one the cable, I can probably find adaptors to fit the cable to BNC ends for the Icom...

[PPG Doug]

Doug,
The choke idea is a sound practice especially with what you are planning. I don't know much about using a ferrite choke as pictured in a previous post as the material it is made of is important for the frequencies you are using.

Lastly, so the ferrite choke(s) I use should match the FREQUENCY I plan on using, not the size of the cable etc... ?

[WHY]

Hi Doug

Might check around some of the "flea markets" and look at some of the old CB antennas, some had cheap coax and some had good coax, can usually get them for around $2 cut off what you need. They are the same 50 ohm impedance. You really don't care what shape the antenna is in.

Tony

[PPG Doug]

Tony:

CB Antennas will work??? I didn't think I could use one...

What about needing a ground plane? I'm still trying to figure out this 1/2 wave stuff etc... :boom:

How about the telescoping style? This thing would sure be appealing from a price standpoint. I like the sound of the Miracle Whip, but I hate to pay $100+. I'm cheap, er, frugal...

[PW_Plack]

CB Antennas will work???

No! That's not what he said! Throw away the $5 antenna - you're only buying it for the cable.

If you have nearby access to a Ham Radio Outlet or Amateur Electronic Supply, I think they'll still sell you coax by the foot in any amount.

By the way, cable that works just fine for CB (at 27 MHz) may perform very poorly in the aircraft band at 122 MHz. A better choice than cheap RG-58 is a cable called RG-8X (sometimes called RG-8 Mini, or RG-8M). It's the same diameter as RG-59, so the RG-59 connector parts can be used for assembling cables in the field, but it's 50 ohms, and has significantly lower loss than RG-58.

[PPG Doug]

A better choice than cheap RG-58 is a cable called RG-8X (sometimes called RG-8 Mini, or RG-8M). It's the same diameter as RG-59, so the RG-59 connector parts can be used for assembling cables in the field, but it's 50 ohms, and has significantly lower loss than RG-58.

SOLD. Will start looking for the RG-8X and the RG-59 screw on BNC ends.

Thanks.

[PPG Doug]

I found on Radio Shacks website that they do carry varying forms of coax.

Radio Shack's descriptions are as follow:

RG-8/U --(/Universal) 50 Used for CB, Ham, shortwave and scanner antenna hookups.

RG-8M --Mini 50 Has a smaller diameter than RG-8, but a larger diameter than RG-8/X. Used for CB, Ham, shortwave and scanner antenna hookups.

RG-8X --eXtra-mini 50 Has a very small diameter. Used for CB, Ham, shortwave and scanner antenna hookups.


Do I want to shop for the cable in that order of preference?
All of these variations have less loss than standard RG-58, is that right?

[RockyMeLad]

Guilty as the source of Scott's antenna. It's naught but a piece of piano wire with a slight taper to more easily fit a female BNC connection, epoxied into a male connector housing so that the tapered tip replaces the center pin, cut off so there is about 23" of wire outside the conector.

I generally avoid RS cables. Very poor electrically and weak mechanically. I prefer RG-400 or RG140 coax (available through AcftSpruce), but they require connectors that are commonly crimped on.

There have been several threads on external antennas. A search should bring up lots of info.

If you can find an amateur radio operator (Ham), they are usually good with antenna/coax issues. Or if you're at BDs, I should be bringing my junque and will be glad to assist then.

[PPG Doug]

So you're responsible eh... I do remember that Scott said something about piano wire, but I could not remember.

Well, you got my attention with the RG 400, but as I have no crimping tools necessary for installing the BNC ends, I'll likely stick with RG-8/U cable. A friend of mine just told me he has lots of the RG-8/U cable I can have.

But...... while I'm at it, can standard BNC ends fit onto RG -400? There is always a chance that if I buy the cable, I might find some crimpers to borrow...

[RockyMeLad]

Yes
Cheap (as in less expensive) is good.
Never tried, but unlikely due to double braid thickness.

[PW_Plack]

Real RG400 is magnificent cable. It's a small, mil-spec, 50-ohm cable with double, silver-plated copper braid shields, teflon dielectric, and low loss. Some military and electronics surplus outlets may have short jumpers already made up with BNC male connectors on each end.

Just read the tiny print on the jacket carefully and make sure it doesn't say "RG400 EQUIVALENT." If it does, it's mystery meat.

[PPG Doug]

Well, I've made some movement towards an affordable try at extending my Icom A6 transmission. I've built a side radio mount to attach next to the throttle on the Dominator.

The cardboard is a mockup of what I'm thinking of for an Antenna Mount on the underside of the Gyro. The brown cable is RG 400 coax. The cardboard (aluminum plate to be...) is a little larger than it could be in an attempt to create some sort of Groundplane, although I'm really not sure if this fits that bill or not.

I have an appropriate BNC "bulkhead" connector to run thru the aluminum plate, but it is not pictured.

Any additional thoughts fellas?

[PPG Doug]

Any idea how BIG the ground plane should be?

Also, should I seperate the groundplane from the rest of the gyro frame with nylon washers, or simply attach it without concern for that?

Thanks.

Doug