Icom a6 ptt

[Mike G]

I use an ICOM A6 on my gyro (M16) with an old PTT switch I've used for years on many different types of aircraft before I flew gyros.
Recently I had a connection that came unsoldered and decided to simplfy the cabling by wiring the PTT direct into the A6 adaptor.
Attached is a sketch that shows what I found.
The ICOM A6 adaptor has a small female socket for the PTT switch. This socket connects the switch simply across terminal at the extreme end of the plug (the bit with a groove) and the inner end of the plug.

When I took my old PTT switch apart I found that it was a double switch and didn't give the same results as a switch connected to the ICOM adaptor cable.

Can anyone explain what the difference is?

Mike G

[MichaelBurton]

The function of a Push-To-Talk Switch (PTTS) is to place the aircraft radio into the transmit mode and connect the microphone audio to the transmitter modulator. This is done by grounding the aircraft microphone jack key (tip) line to airframe ground (normally the “shell” of the mic jack). At the same time a second set of contacts in a newer PTTS closes the circuit between the microphone audio line and the aircraft microphone jack audio (ring) contact. There are two kinds of PTTS. The old style that did NOT have a second set of contacts to break the mic audio line in receive, and the newer design that break both the audio and the key lines when the PTTS is not pressed. I did not compair the diagrams you gave but suspect that the audio line is not connected when you wired directly to the PTTS input.

[Mike G]

Michael
Thanks for the explaination, although I'm not sure I really understood it.
It seeems to me that the ICOM system simply grounds the tip to the case.
The old PTTS I use also grounds the tip and and connects the tip to the middle ring. I hope that makes sense to you.
Mike G

[MichaelBurton]

The tip is the PTTS and the case is ground. Connecting the tip to the case activates the transmit function. The ring is the same as the case, both are ground. On the PTTS with two contacts the other contact can be used to connect the mic.

[Mike G]

Michael
I'm even more confused than before. What do you mean by "the tip is the PTTS"?
Mike G

[All_In]

Michael
I'm even more confused than before. What do you mean by "the tip is the PTTS"?
Mike GPTTS = Push to talk switch!

[MichaelBurton]

When you connect the tip of the mike plug you select transmit on the radio. What I am saying is that the PTTS is wired so that the tip and ground are connected when the button is pressed.

[Mike G]

Michael
OK that's what I thought and that's what my PTTS is doing. I really appreciate your efforts to educate me on this.

I'll try to explain another way.
Looking at the setup before the PTTS is pressed,
The tip that is plugged into the radio is connected to the PTTS and not to the mic plug at all.
The middle ring of the radio plug is connected to the the tip of the mic plug and to the PTTS.
The inner ring (ground?) of the radio plug is connected to the inner ring of the mic plug.

When I press the PTTS
The tip of the radio plug is now connected to the inner ring (ground) of the mic plug.
The middle ring of the radio is still connected to the tip of the mic plug and connected (via the PTTS) to the middle ring of the mic plug.
The connection between the inner ring of the radio is still connected to the inner ring of the mic plug.

Is this correct, and if so why does the ICOM setup only connect the tip of the radio to the ground leaving the tip of the mic connected to ground instead of connected to the middle ring of the radio as with my PTTS?
Mike G

[MichaelBurton]

It is correct to have the mic plug tip connect to the ground only when the button is pressed. The mic tip has no other function. If you connect a PTTS directly to the radio it does not need to be connected to the mic tip. If you connect it in this way then a regular PTTS connected to the mic will not function. The other lines do not need to be changed on most radios. As I posted earlier some PTTSs connect the mic at the same time they select transmit.

[Mike G]

Michael
Thanks for the help.
I wired my old PTTS up as it was and tried it yesterday, unfortunately there was no one at the field due to the very high cross wind. No problem for the gyro so I flew around and now hear myself clearly when I transmitt but seem to have increased interference from the gyro itself. I can hear all the switches going on and off and when the Turbo control unit opens and closes the exhaust gate I nearly deafens me. I've squelched a lot of it out but reception seems to have suffered. I'll try again when there's someone who can hear me.

A stupid question, my antenna is a a straight length of stainless rod with a sheet metal ground plane. Does the ground plane need to be connected to the gyro metal chassis? I just thought about it and since my gyro is a long way away I can't simply check if it is or isn't but should I?

Mike G

[MichaelBurton]

The ground plane acts as the "missing half" of a dipole two element antenna. There should be no need to ground the ground plane. If you have more noise I would insure you have 50 ohm cable to the antenna and look at how the radio is getting power.

[Mike G]

Michael
I'll check it out, although its the same cable as before and it worked OK at the beginning. I realised that the Icom battery charge was very important and this is confirmed by others on this forum and other forums, so I made sure the battery was really charged up.
My plans have changed today so perhaps I'll get to the field tommorrow to play with it a bit more.
Mike

[WHY]

Hi Mike G

When checking out recieve noise, this can be easily tested by using the battery "in the radio" be sure to not be connected to the gyro battery. If noise dissapears then the noise is coming in via the power lead, if you still have the noise then it is coming thru the antenna and must be corrected at the noise sourse.

The ground plane part of a antenna system is probably one of the most misunderstood part of the antena, it is ever bit as important as the antenna it self, ALL ANTENNA ARE MADE OF TWO PARTS, antenna plus ground plane. The first mistake many make is that they try to "run a wire from the antenna over to the ground plane" this is called a"extended ground" and is pure trouble, the ground plane starts at the antenna base connection, and some part of that ground plane MUST BE AT LEAST AS LONG AS THE ANTENNA and prefferably 5% longer. Can be the whole keel length with no problem, it just cannot be shorter than the antenna. Also if there is just one"leg" of the ground plane that is good, this will be the main direction of communication . You only need one leg of the ground plane to be correct to make it work right .

The other mistake is mounting the antenna next to or up right near some metal structure, this is like having a wife and a girl friend in the same house, there is going to be trouble (SwR), the antenna needs to be at least the length of the antenna away from the metal structure. Sometimes a good alternative mount can be done by mounting a BNC connector on the BOTTOM of the keel facing down and using the "rubber duck" antenna pointing down, this sometimes will even help eleminate "flutter" in the transmitted signal which occasionally is caused by the rotor blades, remember the blades are part of the total structure as far as radio frequency is concerned.

Tony

[Mike G]

Tony

Thanks for the detailed education.
I only use the internal battery of the Icom, I'm about to fix up a power supply from the gyro battery to ensure the radio always gets its full 7.2 volts voltage.

When you say the ground plan must be at least as long as the antenna, is the length from the point where it's fixed to the antenna? My antenna is mounted in the middle of an aluminium sheet disc, do I consider the length of the ground plane as the radius or the diameter of the disc? I doubt if even the diameter is longer than the antenna itself, if so would connecting the ground plane to the gyro chassis increase its length or just add problems, could I simply fix a length of wire to the ground plane to increase its length?
The antenna (and disc ground plane) are mounted in the nose of my Magni so its fixed to the fibreglass body but is still very close to the steel chassis. I don't know how I could move it further away.
Thanks again to you and Michael Burton for your patience.
Mike G

[MichaelBurton]

The best radiation pattern will be achieved if the ground plane is equal in each direction. Adding a wire to one side will cause the pattern to distort in that direction. As a note I have seen alumunum foil tape used as a ground plane on composite aircraft. A star pattern would be better than just a straight line. As was pointed out the plane needs to be as long or longer than the antenna for it to work well.

[Mike G]

Michael
I still need to know if the "length" of the ground plane is the radius or diameter of my disc?
Mike G

[WHY]

Hi Mike G

If you are trying to use the "disc" ground plane, then the length for the ground plane would have to be the radius, not the diameter. And yes, the measurement for the length of the ground plane starts at the point where it is fixed to the antenna. I am gurssing the the gyro in your avatar is the gyro you are reffering to, I cannot see the antenna but am guessing it is mounted in top of the nose and in front of the windshield. If so then using a single piece of aluminum tape or a strip of .016 aluminum bonded under the fiberglass and attached to the braid of the coax cable will work "IF" you can get close to the length necessary for the ground plane without making to much of a arch going foward in the inside of the nose, once you bend either the antenna or the ground plane more than 45 degress it starts to degrade the measurements. I'm not sure how long this will need to be, maybe 25 inches or so (Michael can maybe comment ?). This piece of aluminum need only be maybe one half inch wide. If you make this set up, it will do as Michael says, with only the one leg going "foward" , you primary direction of comminication will be in front of you, with shorter directions to the side and back.

Tony

[L_Butler]

Mike,

It's the radius. As mentioned earlier, the ground plane should be slightly larger/longer than the main antenna length.

There are many programs on the internet that will provide you with exact lengths for any frequency and type of antenna.

Larry

[Mike G]

Tony and Larry
Thanks for joining in. My ground plane disc is in the nose of my gyro as Tony guessed. It doesn't have a radius as large as the length of the antenna and it is bent around the inside of the nose of the gyro so certainly breaks the 45° rule. However it did work reasonably well in the past.
I really don't see any way of meeting the ground plane requirements with a gyro unless I put the antenna in the middle of the tail and used the horizontal stab as the ground plane.
I do have another question that may seem stupid to you. The antenna connection to the core of the coax cable is underneath the ground plane (the antenna is on top) so there is a small part of the antenna (about 1") that is close to the gyro metal frame and the instruments and switches and is not screened by the outer core of the coax. Could this un screened part be picking up the noise from the switches and engne and shold I screen it?
I flew again yesterday but there was nobody else there (25 kt crosswind frightens off the ultalight flyers). I enjoyed myself immensly having the base to myself but still hear on the radio all the switches going on and off and worse the turbo waste gate motor as I throttle back or forward. I also heard nobody on the local area frequency but since I didn't get much above 100' it's perhaps not surprising.
Is there a simple way to reduce the interference from switches and little motors? Funny the electric trim motor makes no radio noise just the trim switch.

Mike G

[MichaelBurton]

Noise is usualy a problem when the grounds are incorrectly connected. Only the radio side of the antenna shield should be connected to ground. If you connect both sides you have created an antenna network (groung loop) that will pickup extra noise. All grounds should be kept bundled. You should not have more than one ground wire Going to a radio. The ground or shield should be connected near the radio. If there is still noise after that you can place farite beeds on all wires that connect to the radio except the antenna. The wire goes in a loop through the beed and rejects AC noise. More than one wire can be placed in the same beed. The other thing to look at is the connections on the end of the coax. Make sure that they are undamaged and that the shield does not contact the center.

The hstab would be a good place for the antenna. It would have a much better radiating pattern. The antenna should be close to vertical as it creates a polarized field. The other problem with a horizontal installation is that the radiation pattern will have big holes in front and behind the aircraft. This is usualy the direction where the people are with whom you need to communicate.

[WHY]

Hi Mike G

Have an idea, but would like Michael to comment on it before you try it. Michael , what if he made a right angle bracket from aluminum and mounted the antenna on the flat horizontal part and then mounted a bulkhead type BNC connector to the vertical part of the bracket and connected the center connection of the BNC connector to ground and then installed a " RUBBER DUCK " antenna like goes on the walkie talkie on this BNC connector.

I'm working on the theory here that the nose is fiberglass and there will be no metal near the ground plane component . Most "rubber duck" antenna used on aircraft portable radio's are around 6 to 8 inches long and are of the "helical" design and are somewhat broadly reasonant. While they are certainly not the best radiating antenna around, they do work and maybe the "helical" radiator design could work as well (or as poor) as a ground plane, but would be better than nothing. What do you think????????

Tony

[WHY]

By the way Mike G, do you have access to a SWR meter or to someone who has a meter for this freq range and power range ?

Tony

[Mike G]

Thanks guys I'll be away for a few days, will log on again at end of the week.

Mike G

[MichaelBurton]

Not sure I quite understand the whole thing. The center connection should not go to ground. This should be the signal. Sending it to ground will prevent it from radiating at all. I would not recomend the rubber antenna be used other than on the radio. You could create a ground plane as you have outlined but it may not be pleasant to look at. For a small antenna like the transponder that would work.

[WHY]

HI Michael

Was using the outer part of the BNC connector for only mechanical attachment to the aluminum bracket, the center contact is indeed the "signal " contact but this would be the Part the would produce the "loaded" ground plane and thus was connecting it to ground. all this would be inside the nose.

Tony

P.S. when the helical antenna is used on the portable radio, the outer shell of the BNC is for mechanical connection only and the center or helical coil goes to the radio signal.

[MichaelBurton]

HI Michael

P.S. when the helical antenna is used on the portable radio, the outer shell of the BNC is for mechanical connection only and the center or helical coil goes to the radio signal.

This is because the radio contains the ground plane. This is similar to all unbalanced antenna.

Ok so what I see is that you would have a metal plate that acts like a wire extending out to attach the antenna . This would change the radiating frequency of the antenna and increase the SWR. I would not recommend this type of install. If the SWR gets large then you could damage the radio.

The higher the SWR is, the poorer the match at the antenna, and the greater the amount of reflected power that goes back to the radio.

[Mike G]

I'm not using the antenna from the radio, I'm using a simple stainless steel rod about 1/8" in diameter. It's the antenna that was already on the gyro when I bought it.
In fact I've lost the antenna that came with the radio, I'll have to borrow one to see if the problem is the antenna or the interference from the gyro.

What is an SWR meter?

Mike G

[Chuck Roberg]

What is an SWR meter?

It stands for "Standing Wave Ratio"
Sort of a long explanation.
http://ludens.cl/Electron/swr/swr.html

Shorter explanation.
http://www.absoluteastronomy.com/topics/SWR_meter

[WHY]

Well guys, it sems as though I'm not making the picture clear as to what I'm trying to accomplish here. I am not replacing the regular antenna, that stays as is. I am removing the aluminum disc and just replacing it with a small "L" shaped bracket, to which I am adding a "rubber duck" antenna in the horizontal position to act as a "loaded" ground plane. The "L" shaped bracket will have a "chassis" style BNC connector installed on the vertical leg of the bracket and the "rubber" duck will mount on this connector just like it does on the radio only in the horizontal position, the center pin on the connector must be put to ground for the helicial load of the rubber duck to operate as a ground plane.

I'm not good with pictures on the forum but I have a friend that is, and I think I have enough salvage parts from my old radio shop days to maybe make one of these critters up and photograph it and even test it out since I still have some of my shop equipment which just happens to include a BIRD MODEL 43 swr meter. I don't have the low power element (10 watt) all I have is the 50 watt element but this will be sufficient to check out the swr and tell if the idea is working or not.

If I can find enough parts I will put this together and take photos and have my friend help me post them here and state whether it works or not.

Tony

[WHY]

A note of clarification, the center pin is to be "grounded" to the bracket. The regular antenna is to be mounted in it's normal manner with the proper size hole through the horizontal part of the bracket. This bracket should be about 2 inches wide and each leg should be about one and one half inches long. This bracket will be under the cowl and the antenna will be outside the cowl in it's normal manner. The rubber duck will be under the cowl with the bracket. One very important note, there can be NO wiring or other metal of any size near the rubber duck, especially paralell and near to the rubber duck as this will disturb the "loading" of the helical coil in the rubber duck.

Tony

[RockyMeLad]

Mike,
The shape of the "ground plane" is not critical. I've successfully installed several "ground planes" in composite structures using simple foil tape. Doesn't mater if it's aluminum, copper or ?, and whatever width is available. Just needs to be metal, and not mylar or other metal looking plastic. Typically a plus sign or cross is adequate. More is ok, but usually shows very little improvement. Individual arms of the plus can be bent/folded or even cut short if needed. The ground of the antenna is connected to the foil tape at the center of the plus sign. The glue on the tape often is an insulator, so usually I wipe it off where one sticks to the other letting metal touch metal. Unless you have carbon fiber or static screen in the composite, the plus sign ground plane works fine stuck to the inside of the structure out of sight. Not sure what Tony is trying to describe, but keep it simple...
The center conductor of the coax goes to the antenna (the approximately 23" metal rod sticking out and is insulated from everything else), the shield/braid of the coax goes to the center of the ground plane near the feed point of the antenna.
If you can find a Ham radio operator in your area, they usually have SWR meters and can help you "tune" your antenna system.


Tony,
You're right... I can't visualize what you're describing.
So a couple of questions and I'll try to help.
1- Do you mean by "grounded" that it is attached or directly connected, but not necessarily to metal like the frame?
2- What is the base of the rubber duck antenna? a fine thread screw/bolt? an SMA connector (about a 1/4" female threaded hole with a pin/wire in the middle)? a BNC (slightly larger and fits on a "bayonet" twist coupling)? something else?
3- How are you going to attach the rubber duck to the angle bracket?
4- To what is the center conductor of the coax attached?
5- To what is the braid/shield of the coax attached?

[WHY]

OK RockyMeLad

Thanks for the questions, will try to answer by number #1. by grounded I mean connected to the aluminum bracket, no part of this mounting system connectes to the frame since the lack of sufficient frame metal is the problem. #2. the base of the rubber duck is the typical BNC quarter turn connector. #3. a BNC chassis type connector is mounted in the vertical portion of the bracket, the rubber duck attaches to this, putting the rubber duck in the horizontal position. the center pin of this connector is connected right directly to the bracket so as to make the helical element of the rubber duck the "ground plane". #4. the center conductor is connected to the standard vertical antenna. #5 the braid or shield is attached to the aluminum bracket. both #4 and #5 are accomplished with the typical BNC coax connector that is the basic connector for most aircraft antenna.

The BNC coax connector is the usual standard for most aircraft antenna as it is very resistant to vibration and does not come loose also they go to great effort and extent to mount the antenna in the most un-accesable place possible.

keep in mind that the bracket serves two purposes, a way to mechanically attach the antenna and to mechanically attach the ground plane and to provide a "common" connection for the ground plane and the shield of the coax.

hope this helps with some of the questions, will try to answer any more as best I can.

Tony

[Mike G]

Tony
I can't comment on the feasibility of your idea, as you have seen from my previous posts I don't understand radios or antennas. When you say no wiring or metal near the rubber duck how near is near? I fear this may be difficult in the nose of the Magni but it may be worth a try.
Why do we call it a rubber duck?????
Mike G

[WHY]

Hi Mike G

Not really sure on "how close" is going to be, on a "full size antenna" the rule of thumb is "no metal closer than the length of the antenna" or in this case about 23 inches. HOWEVER, with the rubber duck being typical 6 to 8 inches in length then maybe the condition will be 6 to 8 inches, as I say I don't know. The rubber duck will point foward so metal or wiring that is behind it and a 90 degrees to it will not be critical (like wiring behind the insturment panel).

Last night I finally found enough parts to make up a test model and try it out, will try it out and take pictures and have a friend help me post them on this thread in a few days.

Not sure where the term "rubber duck"came from, to some degree it would come from the flexable ability of the antenna.

Tony

[MichaelBurton]

The shape of the ground plane will change the radiation pattern but as long as it is large enough it will not damage the radio. I don't know why you want to add the small antenna to the ground plane. The SWR meter show how much of the transmitted power is being radiated / reflected. The optimal antenna would have an SWR of 1:1 The first number is always 1 and the second number gets larger. A ratio of 1:3 is as worse than I would accept. The meter can be purchased for around $30.00.

[WHY]

Hi Michael

Not adding the "small antenna" to the ground plane but replacing the "insufficient" ground plane with the "loaded" helical antenna because of limited space, in other words using the helical antenna as a "loaded" ground plane.

Or trying to anyway????

Tony

[kc0iv]

The shape of the ground plane will change the radiation pattern but as long as it is large enough it will not damage the radio. I don't know why you want to add the small antenna to the ground plane. The SWR meter show how much of the transmitted power is being radiated / reflected. The optimal antenna would have an SWR of 1:1 The first number is always 1 and the second number gets larger. A ratio of 1:3 is as worse than I would accept. The meter can be purchased for around $30.00.

I'm afraid a $30 SWR meter won't be very good because of the frequency involved.

If I may I like to make a couple of comments.

While the concept of using "rubber ducky" antennas will work I'm not sure it is worth it.

The "rubber ducky" is a poor antenna performer. Mainly due to it's short length. The "rubber ducky" is mainly used for short distances to and from repeaters.

Leon
(KC0IV)

[Mike G]

"rubber ducky" sounds like something out of a porn shop!!!!

Mike G

[WHY]

Hi Leon

No argument on the "rubber duck " being a poor antenna, but the whole idea around trying to use it as a substitute ground plane is to come up with something that will "work" well enough to be usable and good enough to not damage the radio and fit into spaces that a normal ground plane just wont fit. Although the rubber duck is not the best antenna, it will surprise you how well it works on a gyro when it is install on a good ground plane, like installed on the bottom side of the keel facing down or on a axel. Just ask Chris Burgess.



Tony

[WHY]

Hey Mike G

If it came out of a porn shop and will work as a ground plane -----------well?

Tony

In all seriousness, it wil, amaze you how far a rubber duck antenna will reach when you get just 50 or 75 feet in the air, 20 miles is easy.

[MichaelBurton]

Using an unbalanced loaded antenna as a ground plane is not going to work well.

[kc0iv]

Just for fun I tried a "rubber duck" and a 1/4 wave antenna on my transceiver on several of the local 2 meter repeaters (Close to the aircraft frequency). One of the repeaters could not hear the "rubber duck" and was noise quieting on the 1/4 wave.

I would agree with the right setup just about antenna will work to some degree.

One other problem is the narrow frequency range the "rubber duck" has. Be sure to check the SWR range.

If you check the board history we discussed an antenna (1/2 wave) that I think would work better.

One last comment. Noise should be cure at the source. It can never be solved at the antenna and still have best receiving antenna.

Leon
(KC0IV)

[RockyMeLad]

Well, it sounds like the experiment was to make a dipole. . .
with the center conductor going to a quarter wave element and the shield going to an inductively loaded pseudo-quarter wave at 90 degrees to the first element.

Will it work? Sorta, but very poorly. You could play with "tuning" both elements (real quarter wave and rubber duck} to optimize it at one frequency, but. . .

Like I said the ground plane can be taped to the inside of the composite structure which is curved and even have a short leg, yet still be 95+ percent efficient. The rubber duck dipole thing, IF carefully tuned might get up to 15%.

Over the years there have been several "shortened" ham antennas on the market. Yes, they're better than no antenna at all, but not by much in most cases.

As an example, I use an 8' mobile antenna on the truck with a 100 watt rig. It gets out (transmit) about as well as my 2 watt rig into a decent dipole at the house, but the dipole is not mobile (it's 135 ft long and 60 ft up in the air). Oh, and reception efficiency is equally dismal with the mobile antenna.

So the moral of the story. . .
Stick with a full sized, standard type of antenna whenever possible. Aviation frequencies are well suited for this. Note, this does not mean it has to be an expensive commercial product, but that is an option. In another thread I put a picture of my aviation dipole. Looks like $h1t, but is more efficient than any 1/4 wave ground plane antenna.

[Resasi]

Not the greatest picture but only one I could find that shows our antenna and it's position.

If you look at the base of the stick it is a couple of inches forward of that underneath the keel. Stainles steel tapering rod. Comes out of the base/attachment plate straight then bends about thirty-forty degrees down and is, I think, 21''

Any comments on the placement/length. We have not been able to try it yet so no idea how it will perform.

http://i35.photobucket.com/albums/d165/Paterbrat/Gyrotrailer7.jpg

[WHY]

Hi Leigh

Well, about your antenna, the general rule of thumb on antenna is that it should not be any closer to the keel (or metal) than a 45 degree angle. It looks like such an angle will make the antenna subject to dragging the ground and getting beat by grass. My guess is that if this antenna is measured with a SWR meter it will show some serious SWR.

Your set up would be a prime place to use the rubber duck antenna mounted in a small aluminum plate using existing bolts (if possible) to locate the plate on the bottome of the keel and about 1 inch of plate sticking off to one side just big enough to mount a BNC bulkhead feed thru connector and clear the keel. This would then allow for the antenna cable to connect to the "top" of the connector and the antenna to connect to the bottom of the connector with the antenna pointing down and thus using the whole keel a the ground plane, this has been tried and works well even thought the rubber duck is not the greatest antenna in the world. (it will only stick down about 6 or 7 inches.

Have to "fess up" and tell the whole world that the idea of trying to use the rubber duck antenna as a loaded ground plane was a BUST. Built up a test set up and tried the configuration and the SWR was at a dangerous level, so forget that idea, will post some pictures later to show what did not work and what worked great.

What sources do you have for BNC connectors, don't think Radio Shack will have the bulkhead connectors, will probably need to be a electronics supply house.

Tony

[Resasi]

Tony thank you for that input and advice.

I see a couple of possible alternative sites that would comply with the need for a greater angle from the keel/metal frame than I presently have.

Up towards the rotor head pointing backwards and slanting up and clear of the rotors, though this may get interference from the rotor spinning. Or, under the pod projecting forwards and slanting up.

The rubber ducky in place of the present one projecting down as you have suggested also seems a good possibility that would probably work better than simply having it on the radio.

[kc0iv]

While the best antenna angle will be perpendicular to the mount it is not required. Anytime the angle is NOT perpendicular the radiation will be effected in both pattern and impedance.

As an example your 45 deg angle will cause the radiation resistance to increase over that of an angle that is perpendicular. Which in of itself is not a problem since it can be tuned. The same thing goes for any other angle.

Where there can be a problem is where the radiation element flexes. The more the element flexes the more the element will be detuned.


Leon
(KC0IV)

[WHY]

Hi Leigh

Mounting the antenna up on the mast is going to do like you said and probably get some signal pulsing from the rotor and REALLY get some engine interferrance. Under the pod is not going to work to well as the human body can detune a antenna as well.

Will be doing some testing on the rubber duck "under keel " today and take some pictures to post with the ones on the "ground plane bust"

Tony

[WHY]

Rubber Duck Ground Plane

[WHY]

All of the photos on the Rubber Duck Ground Plane are just to let you know it was a Bust !, forget it!

[WHY]

These pictures show a steel whip ground plane that was 25 inches long and gave excellent SWR reading, direction of communication would be foward with the ground plane whip facing foward.

[WHY]

"And now a word from our sponsor" as they say on TV.

Note the antenna that was used in this experiment,---not the rubber duck but the antenna. It too is a "loaded antenna ", note the slight buldge about 2 inches long near the tip of the antenna, this is a loading coil to help shorten the antenna. This is a new antenna that came with a ELT some years ago and was not used since I already had a good antenna on the plane. This antenna is 16 and 1/2 inches long from tip to bracket. Note how small the loading coil is and that it is covered in shrink material. later photos to follow will show this antenna mounted under the keel/fuselage and at a angle less than the "rule of thumb 45 degrees" and still producing excellent SW.

Also the next group of pictures will show the rubber duck antenna mounted (although crudely ) under the fuselage, this system will work but you have to remember (as others have said) the rubber duck antenna is about as close to no antenna as you can get and have something still work, it is a last ditch effort but does work.

Probably the best compromise for under keel mounting is the "ELT" antenna, it is set for 121.5 MHZ which is right next to the Unicom frequencies and well with in range of operation.

Just a note, check with avionics shops for these antenna since all of the ELT came with a new antenna and usually the plane has a good antenna to start with, one serious point, one style of this antenna uses a coil that looks like a coil spring in the antenna, this is somewhat draggy and want to whip around and would catch grass and everything else under the gyro and YOU DON'T WANT IT.

Tony

PS. Although I could have reduced the angle on the antenna to less than 30 degrees under the keel, these signals are polarized and you will start to loose strength when you go to cross polarization. The angle in the picture was just starting to show some SWR.

[Resasi]

I guess that what I will do as soon as I get back is to try the antenna where it is, see how it does compared to just a rubber ducky on the radio itself mounted on our radio mount. Then progress to the rubber ducky mounted on the keel pointing straight down.

That at least will be our initial course of action. Will be planning the next steps based on information I have gleaned here.

[WHY]

Leigh

Probably the best set up you can go to is the "ELT" loaded antenna that is shown in the pictures, as stated this is 16 and a half inches long from tip to bracket because of the little loading coil and as will be show in some pictures forth coming it was mounted at about a 30 to 35 degree angle under the "keel" with only the slightest SWR showing. This put the tip of the antenna at 9 inches below the keel.

The reason I suggested checking around some of the avionics shops is that they usually have several of these antenna lying around because the original antenna is still good and no reason to install a new one and you might "get a deal"

Tony

[WHY]

The results of using the loaded ELT antenna mounted under the keel and at a 35 degree angle show excellent SWR readings would not reduce the angle to any less so as not to get to much cross polarization on the signal.

[Resasi]

Thanks Tony. Unfortunate thing is I was offered one of those antenna from the shop at Lakeland at a fairly reasonable price but a friend said that because it was tuned to 121.5 it wouldn't be any use. With my knowledge of radios and antennae hard pushed to exceed the operation of tuning and volume knobs I passed it by.:noidea:

One question though, if as you say the body detunes an antenna why would mounted to the pod bracket with its base between the two uprights and pointing forward (ie under the pod) not be a reasonable place as it would be further away from me there and slanting up towards the tip of the pitot tube?

I am saying this just in case you had thought the antenna was pointing back at me.

[WHY]

Hi Leigh

I thought your legs would be near the antenna if it was under the pod.

I was doing my testing at 123.05 and getting next to nothing from SWR, even at that angle. That particular antenna has a angle of about 10 degrees built into it to start with, maybe the shop a Lakeland still has one he would ship you,( or would shipping be unreasonable ).

Can't remember for sure but think that antenna came with the Ameriking model AK450 ELT. If some one offers you one, be sure that it has the small covered loading coil and not the one that looks like a coil spring .

Tony

PS keep in mind not having any serious metal parallel to the antenna or near the tip as it will detune it.

[Resasi]

It would be mounted just slightly ahead of the rudder pedals projecting directly forwards before then tilting up. It tip might possibly get a little close to the pitot tube, but not being there I can't really say, I am only trying to visualize the setup

The one they had in Lakeland was the one with the open coiled spring type, not the covered one.

[WHY]

good deal Leigh that you did not get it. If the line from the pitot tube is not metal you might not have any problem

Tony

[Resasi]

OK so dodged that one

Some frontal views of the pitot tube setup and pod mount.

I had thought of mounting the base of the antenna down at the bottom of the pod mounting bars. Perhaps just in front of the nose-wheel mount and the first section projecting directly forward. The bend already in the antenna would tilt the rest of upwards.

Not sure if that makes the intended location any easier to visualize.

http://i35.photobucket.com/albums/d165/Paterbrat/DSC01609.jpg

http://i35.photobucket.com/albums/d165/Paterbrat/DSC01599.jpg

http://i35.photobucket.com/albums/d165/Paterbrat/DSC01593.jpg

[WHY]

OK, Leigh, I think I'm getting the picture now----- that is a instrument pod and not a full body type pod, and your talking about mounting the antenna down on the keel and facing foward and up ???

Tony

[WHY]

Leigh

That black tube that sticks out in front of the pod looks like metal, think this will produce a problem especially if the antenna want to blow back n the wind

keep looking for that ELT antenna his is what is going to be the best for you


Tony

[Resasi]

Yup it is metal, that is my nose grab handle and Pitot tube. The thin aluminum one I began with lasted about an hour.

That antenna I have is extremely strong and very stiff. I really don't think it is going to do much bending. It was difficult to get the bend in it that it has now, and hopefully it will not be getting too close to the pitot but I will have to try and see what it looks like. If it was still straight it would have been lethal sticking out the front.

Actually I would not like to get prodded by the pitot either that is really sturdy.

Anyway Tony I've been given some good ideas to try out and we will just have to see what is best.

[RockyMeLad]

Leigh,

Looks like my response didn't get uploaded, so will try again.

I can't see your antenna in the picture, but your description is of one of the better locations for this type gyro. Under the keel, using the keel and everything electrically attached to it as your counterpoise, about centered from other metal (landing gear, etc), straight down as far as possible then bend back at 45 degrees to clear ground/grass/etc. Just don't want to hang up on something when pushing the bird back.

Yes, there will be some interaction between that antenna location and real ground, but not usually serious. If you can hang the bird as clear of the ground as feasible (like doing a hang test) when tuning the antenna, you should have good flying results. I've successfully tuned Dominators sitting on the ground with this antenna location, and they're not much taller than your bird.

Another decent location would be the top/front of your pod. Your counterpoise could be metal tape on the inside of the pod. Probably only three would fit that pod, and even if you had to shorten one a bit it should still work. Ideally from an RF view the ends of the tape away from the antenna base shouldn't touch. Another option for the counterpoise would be a good ground braid from the base of the antenna to a good electrical connection through the pod to the top of your mounting post. Then like the under-keel location all the "frame" becomes the counterpoise. On rare occasions I have seen strange resonant lengths of metal cause problems, but this usually works. The top of the pod antenna also makes an excellent place to tie your yaw string.

Then of course, there is the infamous Rocky's Ugly Dipole. . .

[Resasi]

Paul in my original picture of the gyro on the trailer, if you looked at the base of the control stick just forward of that are the bracing struts for the main gear that comes back to the main wheels. You can see the port side one clearly.

Below that, just forward of that on the bottom of the keel you can see where the base of the present antenna is mounted. It projects straight down about an inch and then is bent backwards at about a thirty degree angle.

Not a great picture of it and it is barely visible but you can see it.

Actually the tip, which we cut off as it was too long, is mounted on the top of the pod for my drawstring.

When I get back I will try it where it is then if the results are bad will then begin casting around for a more suitable/successful location.