Radio Noise

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I'm getting alot of noise based on Engine RPM. I think my ground wire for the engine is transmitting this noise. Any idea on how to shield against it?

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[Udi]

John,

Have you used shielded wires for the engine kill switch, the tachometer, and the electrical charging circuit (rectifier)? If not, this may be your problem.

Udi-

[barnstorm2]

Also, try resistor style spark plugs and keep the antenna away from the engine and direct contact with the airframe.

[PW_Plack]

John,

Describe the "noise." Is it a cracking or "staticky" sound, or a whine with a definite pitch which rises and falls with RPM?

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UDI

My wire isn't shielded. I only have the one wire from the magnito to the ground with a switch in between. Yes my RPM gauge is also connected to iether side of the switch.

Barnstorm,

My radio is straped to my leg and is self contained and battery powered. No external anntenas of power sources.

Paul,

It is a staticky sound that increases and decreases in pitch with the rise and fall of engine RPM.

I just bought an intercom from comtronics hoping this will clean up some of the noise. I'll, of course use it on the "DaLil-Wang."

What do you shield a wire with?

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[Caribean_gyro]

wire mesh. Have you seen the tube that conects the toilet tank to the valve. They come shielded to protect for over preasure.

You can buy this cut the tube and use the wire mesh jacket. Mount it on the spark plug cables and ground 1 side to the chassis. This is the cheap wire shielding you can get.
Chuck P

[Udi]

John,

Just go to your nearest electronics store (Radio Shack) and buy a shielded wire. The wire is wrapped in metal foil, which you can screw to ground. When the wire is not shielded, it acts as an antenna, transmitting the magneto pulses to the atmosphere. This is very easy to fix. Replace it all the way to the tachometer. While you're at the store, buy a flexible coax extention cable for your radio, and mount an external antenna on your instrument pod. This will further reduce noise and increase the range of your radio.

Udi-

[steveb]

I had a problem just like this one, and spent lots of money on new plugs and shielded / resistive plug caps. I finally solved it when I replaced the plug leads, which was probably about the cheapest and easiest thing I could have done!

[Screw]

Thanks all,

I'm gonna try Udi's suggestion and buy some pre-shielded wire and mount an external anntena.

John-

[KenSandyEggo]

This is weird. I posted a reply and must have hit "Preview" and then exited. DARNIT! I did colored text and everything!

Anyway, try this cheap (costs nothing) thing first before you start buying shielded wiring, special plugs and plug wires, electronic filters and half of Aircraft Spruce's catalogue. My Avid Flyer had a Cuyuna (Crap-una) engine without any shielding.

A lot of hand-held radios have their internel microphone open when you key the mic, even with a headset attached. In other words, both open. Your voice comes through the one on the headset, but the internal mic of the radio picks up all the engine and air noise and screws everything up.

Open the case, find the teensy mic, usually near the grill, and snip one of the mic wires. I had the same thing driving me nuts (and you see the result), until I snipped the wire. The radio then sounded as good as 2 tin-cans connected by a nylon string instead of cheap packaging twine.

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Thanks Ken, I will try that too.

UDI!!!! Any suggestions on an extenal mount antenna for a hand held? Like a part number. Aircraft spuce offers so many antennas, I don't know whick one to go with. I got the shielded wire and rebuilding a pod. I might as well do the antenna thing, but I need to know exactly what to get.

I have an older sporties JD200 handheld, I need to know: What antenna, and what to put between the radio and antenna (Coaxial cable?)

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[Caribean_gyro]

http://www.aircraftspruce.com/catalog/avpages/com_comant.php

this are broad band antenna. there are others but this is what I have use
huckP

[Caribean_gyro]

also use 50 ohm coax cable. rg 58au. there is a thinner jacket cable I use but handle less power. I think is rg175u. but you have to check.

RG58u is normally foun in Raio shack
chuckP

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That's alot of money Chuck.

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[gyropilot]

I'm using this one on my GyroBee with very good results:

VHF Comm Antenna (http://www.aircraftspruce.com/catalog/avpages/av534.php)

http://www.aircraftspruce.com//catalog/avpages/p421graphics/av534.jpg

$50.00 at Aircraft-Spruce... you could probably find it a bit cheaper if you shop around.

Good luck,

John L.

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That's more like it!

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[CLS447]

John L. , I think Skysports has that same antenae. Do you use it only for you aircraft radio? Would it work for a CB also? I imagine your lead is pretty short... Did you have to have it tuned in for proper operation? Any ground plane needed? Does the transponder need antenae connection?

John S. , Did you try any of the suggestions given here yet? Have they worked?

BTW Shar & I have decided to send back our one Comtronics helmet (Standard w/ flip up muffs) to exchange for the 2000 model. Definitely more comfortable and has better sound attenuation. Same price. Just wanted to see for myself.

[Caribean_gyro]

john just make sure you dont move in the whole frecuency spectrum the whip is cut to mid range. working it at the edges will eventually burn out the output transistor on the handheld.
chuckP. also pick up more static

[PW_Plack]

Chris,

The antenna in John's picture is a quarter-wave ground plane, designed for use on a metal-skinned aircraft. If it's mounted to a fiberglass surface, it should have a metal ground plane mounted beneath the fiberglass. This could be as simple as two 24-inch wires, (assuming an antenna cut for 122 MHz,) connected to the part of the antenna base where the coax cable's shield connects, and extended out from the bottom of the mount in opposite directions. Don't coil the wires, but it's OK to curve them to follow the inside of your pod, and they can be glassed, glued, taped or epoxied in place.

Wires shorter than 24 inches will help, but the antenna's impedance will be a poor match to what the handheld's output expects to see, and performance will suffer. A metal ground of random length and shape, such as your airframe, may produce a good impedance match to the radio, but a distorted radiation pattern. (The antenna tends to perform better in the direction of the majority of the metal.)

In John's case, it looks as though his mount has RF (if not DC) continuity to the frame of the gyro. I've seen a couple of Dominators with similar mounts installed through the nose pod with no ground. They probably barely work at all.

When a quarter-wave antenna is mistuned or operated without a proper ground plane, the outside of the coax cable's shield becomes "hot" with RF current. So will the DC power lead to the radio, and many other wires in your harness. This does more than produce poor radio performance. It can also result in transmitter energy being coupled into your avionics, fuel injection or ignition computer, or other places where it can cause trouble. It also increases pickup of pulse type ignition noise, the kind you get from your ignition wires. Misrouted RF can, in extreme cases, even scramble the radio's own microprocessor, randomly altering the frequency on which you're transmitting, or cause loud feedback squeals on transmit.

If you want a good, inexpensive quarter-wave antenna for use on an experimental or ultralight, see if there's a Ham Radio Outlet or Amateur Electronics Supply store near you. Tell them you want a quarter-wave, vertical, mobile antenna for mounting through a hole, resonant at 122 MHz. It will need to have a whip at least 24 inches long. It will come with a cutting chart, with directions on how long to make the whip for the frequency you want. If you have access to a standing wave ratio meter rated to 150 MHz, you can trim the finished installation for optimum performance. If not, follow the cutting chart carefully.

This type antenna will work most efficiently if left straight. The bend in aircraft antennas does little for aerodynamics, and probably became popular because the bend increases ground clearance when belly-mounted. Keep the antenna clear of any parallel metal tubes or other surfaces within a couple of feet for best results.

Valor and some other brands have these antennas for under $25.

If you absolutely cannot fit a ground plane, and have to mount in fiberglass, see if you can find an antenna designed for marine use. I've never seen one tuned for the aircraft band, but I've seen stranger things!

Ham Radio Outlet or Amateur Electronic Supply will also have coax cable of better quality than Radio Shack's. RG-8X or RG-8 Mini cable are .242 inches in diameter, and have lower loss at 122 MHz than does the slightly smaller RG-58. Never use anything smaller than RG-58 for the VHF Aircraft band. If your antenna comes with way more cable than you need, don't coil the excess...cut it back and re-attach the connector. If you're not experienced with solder, get help! Bad solder jobs kill the performance of many antenna upgrades.

By the way, the difference between a "rubber duck" antenna and a full-sized quarter-wave antenna with a good ground is typically 10 dB or more, equivalent to a ten-fold difference in power. A handheld radio with a good external antenna can outperform a full-sized 10-watt aircraft radio with a mismatched antenna. I'd bet most people who are disappointed with the performance of a handheld have something seriously wrong with the antenna installation. A 1-watt handheld with a good antenna and mic setup should have no trouble communicating over a 20-mile radius.

[Aussie_Paul]

You guys will contine with 2 strokes won't you!!!!!!!!! LOL

Aussie Paul. :D

[CLS447]

Paul P., I don't ever print things from this forum, but I'll be printing your post! Thanks alot! I'll be looking for you when I have more questions on this subject.

Paul B. , Years ago, I spent a small fortune on my Comtronics Heli-pro helmet & Icom A-20 & Radioshack handheld CB for my 2-stroke Air Command. The same patch cord fit both radios. Good thing because the cords are $90 each. I got so much noise, I gave up and I only use the helmet. It's better than the Simpson Bandit that I use to fly with because its lighter, protects what left of my hearing better & looks more aviation-like. I doubt it would protect my head as well ,though.

I've talked to alot of people about it but I didn't feel like shielding everything on the ship. So I have never spoke to a single person with it from the air! It works great when walking around on the ground, except for reception.

As you know, my new machine is Subaru powered. I just spent another $600 for Comtronics Dual-com intercom with 2 matching helmets. Can switch between 2 radios & has music input. This system is gonna work IF IT'S THE LAST THING I DO !!!!!!!!

[rehler]

Paul Plack,

Please describe the "added wires ground plane" concept a little more.

Which direction should the two wires run, fore-aft or side-to-side?

Would 4 wires be better, sticking out fore, aft, left and right?

Are these wires just single wires, all attached together and to the base of the antenna?

Thanks.

[PW_Plack]

Ken,

Four wires would make a slight improvement in performance, and should make the antenna's radiation pattern more nearly omnidirectional. Few pods, though, have room for 48 inches of wire end-to-end.

I've done VHF mobile installations through fiberglass truck caps and the like, where I've made the ground plane out of a 2-inch wide piece of 1/16-inch flat aluminum stock from Home Depot, with the mounting hole for the antenna base cut in the center. (It ends up looking a little like a lawnmower blade.) This method also reinforces the hole under the mount. A 48-inch piece of flat stock would not be practical under most gyro pods.

The quarter-wave ground plane antenna is among the easiest to fabricate and usually works well if the dimensions are close. The formula for approximate lengths of elements made from wire are:

2800 / Frequency (MHz) = Length in inches for the antenna rod

2950 / Frequency (MHz) = Radius in inches for the ground plane

The lengths will need to be slightly less for large diameter tubing, but we're not likely to want to do that in this application. Connections are made as follows:

http://www.voiceswest.com/groundplane.JPG

Please pardon my crude skills with Microsoft Paint!

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Yall are way over my head! I have some shielded wire and an intercom on the way. I'm waiting for my new pod to get out of the paint shop. At which point, I will re-mount my kill switch to the pod using the shielded wire from the mag to the switch, RPM gauge, and ground.

About the antena. I have an old Sporty's JD200 radio (Battery powered 4AAs). I am looking for a simple extenal antena I can mount somewhere on the airframe or pod and have a cable connection between the two to improve range. That's all. I do not have an internal battery on "DaScrew-Driver," and I'm currently strapping the radio on my leg. However, I have a GPS mount and I am working on mounting the radio and an intercom to each side of the GPS mount.

The goal is to sit down, buckle up, plug in helmet, and go fly. Unfortunatley, if you've been reading my postings, I'm not very bright. I know less about radios.

Help!

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[rehler]

Paul Plack,

Your drawings is great. The 2" wide aluminum plate idea seems like a really simple way to make a ground plane.

Thank You.

[Caribean_gyro]

I use a copper board from radio shack that has a copper foild on both size. Is 4 inches by 8 aprox. this is plenty of ground plane.

Pauwl you tune also the coax lenght to bad multiples right? When I use to have the whip beside cutting the whip the lenght of the coax improved the VSWR.

I steel feel that for the cost delta and the hassle of tuning the whip the coiled version has a better performance. This takes care of the nosie but the radio/microphone match also makes a diference.

Chuck P.

[PW_Plack]

Chuck,

If the antenna is properly tuned, there will be no change in the standing wave ratio (SWR) seen at the radio end by changing cable length. A 4-by-8-inch piece of circuit board is nowhere near big enough to provide an adequate ground plane to make a 122 MHz antenna tune correctly.

Assume you have a radio transmitter designed for a 50 ohm load impedance, and 50-ohm coax cable such as RG-58. If your antenna is properly cut for the frequency, and has a proper ground plane, it will be 50 ohms, and the impedance anywhere along the length of the cable will also be 50 ohms.

If the antenna has some other impedance, then the impedance "seen" by the transmitter will vary depending on cable length. As you noted, you can cut the cable in a mismatched system to a length which results in the connector being at a magic 50-ohm spot, but this does not improve antenna performance. Some transmitters with SWR-sensing protection circuits will deliver more power into a mismatched antenna using this trick, but some of the extra power gained will be dissipated as heat in the cable. More important, the audio distortion and feedback, and possible more serious problems with interference to EFI or ignition systems, will still be threats.

Back in the 1970s, when CB radios were so popular in the US that even JC Penney sold them, most CB antennas came with pre-fabricated 17-foot RG-58 coax cables. CB-ers came to accept that this was a magic length which "boosted power." In reality, it was just designed to mask the side-effects of sloppy do-it-yourself installation practices, prevent transmitter damage, and minimize the number of antennas returned as defective.

There are special cases, including the multiple antenna systems popular with truckers, which use this cable-length trick to create impedance transformers. In our simple single-antenna systems, length of the cable should not matter.

If you can find a ham radio friend who operates on the two-meter (144 MHz) amateur band, he may have an SWR meter operable on aircraft frequencies. Better yet would be the popular MFJ (brand) antenna analyzers, which can tell you where the antenna is tuned very quickly, without keying your transmitter. Either way, make your tests in an open area away from metal objects, late at night if possible, and at least a few miles from an airport. Even the MFJ analyzer emits a tiny signal which could interfere with aircraft communications in your immediate area. If you must use your transmitter to drive an SWR meter, always listen on a frequency for traffic before transmitting.

[Caribean_gyro]

Paul I am having some issue with my web page so I will replay to you inputs above. Thanks you have put me to go back to my Ham roots. Just a note. If you dont have a tuner between a transmiter and the 1/4 wave antenna to match impedance then you are asking the cable to do this for you. Again I will replay tomorrow.
chuckp

[PW_Plack]

Chuck,

If you build a 50-ohm, unbalanced antenna and feed it with 50-ohm, unbalanced feedline, there should be no need for a tuner to match it to the 50-ohm, unbalanced output of your radio. If you're an old ham, find a copy of the ARRL's [/I]Radio Amateur's Handbook[I]. The older editions used to show you how to make a quarter-wave VHF ground plane for mounting on a vehicle roof, using just a pair of UHF connectors, a 19-inch piece of eighth-inch welding rod, and a little solder and epoxy. I had one on my 1964 Chevy, built at a cost of $4 with new connectors.

Of course, the book (http://www.arrl.org/catalog/index.php3?category=Technical%2C+Electronics%2C+an d+Communications+Reference) now costs $35...

[ToddP]

After reading this, I'm thinking my best course of action is to:

Load up my gyro, haul it to Portland and have Paul setup my antenna. :)

[CLS447]

Todd, great idea! Maybe I'll meet you there & we will get a 2 for 1 price! LOL

[PW_Plack]

What price? Bring 'em to a Chapter 73 meeting some second Saturday, and give me a little advance notice. There's even a Ham Radio Outlet store here in town.

[Udi]

What a great discussion! Thanks for the great info, Paul!

I have a whip antenna, just like Landry's. It's 23" long, which is just about 1/4 wavelength (it will tune perfectly to 121.5, which I hope to never need!!!). The antenna is mounted on my Air Command instrument pod, and I have a metal wire mesh for ground plane. The ground plane is not large enough, but as large as it can be without sticking out of the pod. It is 7 inches fore and aft (total 14), and 4 inches right and left(total 8). I know this is not optimal, but I hope it will work out ok. Paul - do you think a wire mesh is a good idae?

John - let me know if you are still lost; this is a no brainer. With little effort you can have a good system!

Udi :cool:

[PW_Plack]

Udi,

I've seen guys use eveything from window screen, to aluminum roof flashing to foil. They can all work if they're big enough. A mesh screen of the size you mention will help, and will produce an SWR dip at the design frequency, but will usually not reach the desired 1:1 match.

Did you have access to an SWR meter with which to refine the whip length? If you can get one, and the mesh isn't permanently glassed into the pod, try replacing it with a 48-inch piece of copper wire, attached at the center to the antenna base's coax shield connection point, and routed beneath the pod, even if you have to bend it around. Make the bends as gradual as you can, and try to keep the ends of the ground wire away from metal airframe components. If it doesn't work any better than the mesh, stay with the mesh if it's more convenient.

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Udi, I'm still lost. Please post what I need to buy and install before I lose my mind.

screw-Out

[Udi]

John,

If I were you, I would buy a whip antenna, just like Landry showed, from Aircraft Spruce. The antenna is already cut to aviation frequency. Go to Radio Shack and buy RG-58 coaxial cable. That's an antenna cable. Buy 1 male BNC connector - you will solder this connector on the radio side of the cable. If you can't solder, find someone who can, or buy a cable that already has a male BNC attached.

Some people attach the antenna to the keel, behind the prop, and use the keel itself for ground plane. Others attach it to the pod. If you use the pod, you have to make a ground plane. The ground plane is just a piece of metal (preferably 48 inches long). See Paul’s schematic. The RG-58 has two wires - a signal wire, and a ground (the shielding). The signal (inner) wire attaches to the antenna (screwed on mine), and the ground attaches to the base plane (usually soldered, but you can screw it on).

As Paul explained above, the quality of your ground plane will determine how well your radio will transmit and receive. You can follow one of Paul's ideas for a ground plane.

Does this sound manageable?

Udi :cool:

[Udi]

Paul,

I bought this pod already made. The screen is glued to the pod. I'll mess with it only if it doesn't work ok. I will test it hopefully within a month.

Thanks again!

Udi :cool:

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Thanks Udi! I'm on it.

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[eruttan]

But RG 400 instead of RG-58 if you can find it.

[Caribean_gyro]

First the tread was meant to noise reduction and we went more technical into antenna selection and tuning . Opinion around a quarter wave antenna vs. a 5/8 or full wave antenna. which one pick up less static noise.

First I will like to set some base lines. The whip antenna is a quarter wave length with no radials and no gain . I have calculated the length the antenna should have at low,mid and high end of the aviation frequency spectrum.
118 MHZ 1.983 feet = 23.8 inches
122 MHZ. 1.918 feet = 23.0 inches
134 MHZ 1.746 feet = 20.95 inches

So it changes 3 inches on the full spectrum. There are 3 alternatives to work the SWR
1: Tuned to mid frequency and hope to get a swing to a max of 2:1 on either low or high side of the frequency.
2: Use an antenna tuner to adjust the mismatch
3: Use a coiled Antenna . Tuned to with stand a max swr of 2:1 on the full spectrum.

A quarter wave transmitting antenna may be efficiently loaded up to about twice its resonant wave length by the insertion of an antenna inductance or it may be shortened down to about three-fourth of its resonant wave length using a series of condenser "antenna Tuner. I have yet not found any GA aircraft with a tuner.

You have to give allowance for the coupling of the inductance necessary in the transmitter, which means that the resonant wave length of the wire(coax) from the antenna to the transmitter should be 25% lower than the lowest working wavelength. SO cable length should be around multiples of 17.9 inches.

Every antenna has an impedance express in ohms, same as the feed line and the transmitter side. The reactance combination plays a key role here. Just see "reactance" as the opposition to the flow of AC signal in a circuit. Radio+coax+antenna is a circuit. Radio Power "RF" equals to AC signal.

The impedance of the antenna depends on several factor, including the length,operating frequency,height above ground, surrounding metals and even weather.

The impedance of the cable depends on how is constructed. The unit of measurement of gain or loss is called DB. So the coax cable loss is measure in DB/100 feet. Example 10 DB loss in 100 foot= to 1 DB for every 10 foot.

Now 3 of the most popular cables are RG174,RG 58U, RG8. The 174 is the thinner cable .110 overall dim. then is the 58U that is .195 and then RG8 that is .240. The ticker the better for low DB loss and fast propagation velocity but weight more per feet. It also a thicker coax present a problem to the connectors. in the whip antenna you just strip the wires, but the other antennas you need a BNC connector and RG* need to be adapted to this connector.

RG174 RG58 RG8
belden cable 7805R 7807A 7808A
50 MHZ DB/100 4.6 2.1 1.6
150 MHZ DB/100 8.0 3.7 2.8
220 MHZ DB/100 9.6 4.5 3.4

Your feed line does more than simply connect your radio to your antenna. It acts as an impedance transformer. The impedance of your antenna is transformed by the feed line in to the value your radio sees when you connect it to the cable. This impedance act as a load to your radio. Most radios are designed to work with a 50 Ohms load. But if your radio don't see 50 ohms you have a mismatch.

In a mismatch a portion of the power "RF" is reflected back down thru the cable to your radio. This reflected and forward power creates the SWR in the feed line.
Now a 1:1 SWR indicates no power is reflected ,meaning maximum power is been transfer to the antenna. A higher SWR can cause damage to your radios or poor transmitting range.

Many new radios have now SWR protection circuit when SWR gets too high it reduce power or it shot off the transmitter.
If you have a Certified aircraft your radio output is around 10 to 25 watts. A handheld radio output is 1 watt. So when you have high SWR in a 25 watt radio even if the protection circuit reduce power you will still have enough been deliver to the antenna . But in a handheld you need every single milly watt the get heard.

My suggestion a coiled antenna as the RAM or Commant VHF , a low loss cable coax as the belden 7807A a good ground plane connection. Located the antenna 8 foot away of the transponder antenna and in an area free of obstruction so it can reflect 360 degrees.

I wrote all this up trying to clarified some ideas or perception of Radio and antenna tuning. My old days of communication have been displace by the computer world so this type of discusion great .

Supporting data can be found in the Ham Radio handbook, WWW.eham.net, Technical glossary http://www.coasteltools.com/glossary/glossary.htm Cables at www.belden.com, Steve Ford QST. www.cgsnetwork.com/antennagpcalc.html
:)

[PW_Plack]

Chuck,

If you're using feedline as a transformer, yes, length matters. But the reactance you mention assumes an out-of-tune antenna. When tuned for resonance and a 50-ohm impedance, the inductive and capacitive reactances in the antenna, "seen" by the radio through the feedline, will cancel for a net reactance of zero, requiring no transformer.

5/8-wave and full-wave antennas offer "gain" over a quarter-wave, and 5/8-wave antennas are popular on cars, but they achieve this gain by directing the bulk of the transmitter's power toward the horizon. This is NOT what you want in an aircraft, where your life may depend on being heard by others directly above or below you.

In practice, I find that the 1/4-wave ground planes I build will stay under a 2:1 SWR over a range of about 2.5 per cent of center frequency without a tuner. SWR will decay more rapidly below the resonant frequency than above, so if you cut for about 120 MHz, your transmitter will probably stay happy from 118 to 123. If you think about it, it will be rare to be transmitting outside that range. In nav/com radios with separate sections, you'll want a separate, horizontally polarized antenna for the navigation frequencies anyway.

As for using an antenna tuner in an aircraft, maybe something like the new automatic tuners could be effective, but the workload of a manual tuner would be nuts. (Although, I do recall seeing morse code keys on a leg strap used by early aviators to communicate with ground stations!)

I generally avoid UG-174 coax like the plague, not because it's lossy, but because it's fragile. If you want to broaden the frequency spread over which an antenna will stay within 2:1 SWR, the additional loss in UG-174 will actually help. The broader useable frequency range of the helical antennas (including the "rubber ducks") happens because the coils are lossy.

(I've edited a misstatement I made in a previous post about too-small ground planes causing narrower bandwidth...actually it's just the opposite. A too-small ground will, however, allow the antenna tuning and SWR to vary more in response to nearby objects, including your legs moving under the pod.)

Ham radio antenna builders sometimes work well past the point of diminishing returns in seeking perfect antenna tuning. In an aircraft, if you get things close enough to make the radio work properly, and keep noise out, consider it a success. Most problems in mobile radio systems happen when connections come loose, so have the fewest connectors and adaptors possible. Even one watt with a decent antenna will work great at hundreds of feet above the ground.

[Caribean_gyro]

Paul :
To be tuned the radio needs to see a low SWR. The capacitance and inductance of the radio,cable and antenna is not the same. Unless you use a Balum or "tuner" we will have a reactance varying with the frequency. This is what I ment that the cable plays a big role in the tuning process. When I mounted my whip I tuned it to mid freqeuncy myswr was at 2:1 I never acomplish anything lower. But I work in 122.8 in my airport there it got wroth. I adjust my cable as I menyioned in wavelength multiles and I got back to 2:1.

I was heard at 800 feet around 2 miles. When I switch to the Coiled antenna I even got fix wing asking what I did I was been heard farther and lowder. I am a freak of good radio comunication. The gyro can not be see easyly plus fixe wing pilots see using the radio. SO I want to make sure that when someone mounts a handheld it drives the more power as posible,

Not too many persons have a SWR meter.

AS for the rg174 the only advantage I see is thin and you can rout it in the gyro angles that it bearly show there is a wire. But performance sucks.

I agree the nosie issue is a compilation of many factors. I got a guy that ask me for help in his plane whe develop noise on landing not in flight. SO first suggestion as dont talked on landing. He didnt like that one.

Problem was alternator was not putting enought output when the light was turn on. Bottom line to the person saking noise reduction you have to attack all posible solution give here 1 at a time until you get to a confort level.

Chuck P. :)

[PW_Plack]

Chuck,

I understand what you're saying - we're just picking two different methods to solve the problem of a 2:1 SWR. If the antenna shows 2:1 at resonance, it's nowhere near 50 ohms impedance. I prefer to work on the antenna, since getting it to 50 ohms will make the impedance constant regardless of cable length, but you can certainly cut the cable to a specific length to transform the mismatch as an alternative.

A balun, which is short for balanced-to-unbalanced, is never needed with a ground plane antenna. The ground plane, coax feedline and transmitter output are all unbalanced. There's no place in the system where you need to convert from one to the other. A balun of some sort is needed if you're feeding a balanced antenna, such as a dipole, with coax. The dipoles designed to be hidden in a fiberglass fuselage have a balun built-in.

Worrying about cutting cable to offset the reactance in the transmitter output is, IMHO, not a productive use of time. At it's tuned frequency, the capacitive and inductive reactance in the radio's output stage offset for a net reactance of zero. Ditto for the antenna. The coax has a characteristic impedance of 50 ohms regardless of frequency.

The coax performance figures you quote are for a 100-foot length. If you have a run of 10 feet or less in your aircraft, the difference in performance between UG-174 and RG-58 is less than half a dB at 120 MHz, which will require sensitive test equipment to measure. It's not enough to make a difference in whether you're heard. The losses introduced by a helical antenna, undersized ground plane, or 2:1 SWR will all be much more noticeable.

[Caribean_gyro]

Paul bottom line I like to move in the whole spectrum here in PR. I have many airports and tower frequency to deal with. so I like to know that my radio is not suffering. I would not recomend the whip antenna. AS a matter of fact I have 1 brand new in my hangar for $45.00 with cables and instruction for any one that want it. I will stick with what have work for me .

bUt did enjoy our diference views on antennas. Like to see that not only aerodinamics is the discusion in the forum.
fly safe
ChuckP.

[PW_Plack]

Chuck,

If you need the whole range of the aircraft band, an automatic tuner sounds like a reasonable soultion. I haven't looked at the Icom aviation radios...do they have the same serial data inputs/outputs as the similar ham radios? A small microprocesor set up to read the radio's current frequency, then switch tuned circuits to optimize the antenna for the frequency in use, would seem feasible, and simpler and faster to react than an automatic tuner.

There are also special antenna designs which allow a ground plane antenna to cover wide frequency bands, but they're pretty bulky. They wouldn't be aerodynamically suitable for an aircraft unless they could be enclosed in a fiberglass vertical stab.

Hmmm...

I appreciate any discussion which provides new ideas to think about!

[Udi]

Chuck,

Would you describe what is a coiled antenna, and how to build one?

Thanks

Udi :cool:

[Caribean_gyro]

A coiled antenna or tuned antena Is a fibelrglass whip with a metal rod inside of it and a coiled to similuated the transimter that you frequemncy wavelenght is changing as you move up or dwon in the frequency of operation.

In HAM radio you use a tuner to adjust you loss to a min as you move in frequency . This we can not do as we fly. What I use is a set up that guarantee a maximum swr that will not damage your radio and will give you the best performance tradeoff.

http://www.aircraftspruce.com/catalog/avpages/av529_568.php
http://www.aircraftspruce.com/catalog/avpages/avt10_14.php
http://www.mikesaircraft.com/comant_antennas_couplers.htm#VHF

[rehler]

John,

When you install the shielded wire, ground the shielding at both ends. This is what Rotax recommends.

[GeneWeber]

Hi Paul & Chuck P.,

What do you think of the “Special 1/2 Wave antenna with Loading coil”, or the 1/4 wave “AIRKIT” dipole antenna? (For those of us who simply cannot fit a decent ground plane)

http://www.wingsandwheels.com/page14.htm

Thanks & Regards,

Gene

[Caribean_gyro]

my first question to them is waht is you SWR from 122 to 124 mhz. It seem she is tuned to a high frequency. Now I am not very excited to antenas with out a good ground plane. a coat hanger will recevied great, but what happen when you put Power to it? a dipole is 2 elements and again is normally cut to mid frequeny. and for 09 I know there are cheaper out there. Let me check some url and I will post them
chuckp

[Caribean_gyro]

here is an url
http://www.aircraftspruce.com/menus/av/antenna.html

here the cost go from 94.00 to 125. the only diference is whip angles and speed.

But if you want one chep I have 1 looks like a shark fin will hold 200 knots and is yours for the cost of the freight
chuck

[CLS447]

Ken, you are an artist! Looks very, very nice! How soon?

[GeneWeber]

Hi Chuck,

Thanks for your reply. I will ask them that, and any other questions you care to suggest.

I’ve never done anything with antennas before, so this is an unfamiliar topic for me. From the little bit I’ve read so far it sounds like a ¼ wave antenna is a monopole, driven single ended, and requires a ground plane to “reflect” the “missing half”. A ½ wave antenna is a dipole, driven differentially, the top half being the whip and the bottom half being a coil. It requires a balun match the difference of impedance between the whip and coil.

Based on that I would have expected the “AIRKIT” antenna to be ½ wave, but it is marked ¼ wave on the picture. So obviously I don’t yet have a complete enough understanding.

Best Regards,

Gene

P.S. Chris, I wanted to call you on Father’s day but was busy with family all day. Looks like you went flying on that gorgeous day. Please give me a call, or send an email sometime when you are free, and I can see your plane.

[rehler]

Chris,

I assume you are referring to my web site. Thanks.

How soon? If you are asking about my gyro alterations, I am completing the additions to at this time (hope to add gas and fire up the new engine Sunday). I plan on flying it at Mentone in just a few weeks. Today I ordered a new enclosed trailer, which is to be ready July 15th, so I can haul the gyro to Mentone in style.

[CLS447]

Alright Ken!, Hope to see you & the machine there!!!!!

[Udi]

Today I ordered a new enclosed trailer, which is to be ready July 15th, so I can haul the gyro to Mentone in style.

Ken - I think you can FLY your gyro to Mentone in style!!! Have someone else drive the darn trailer! This is what I am hoping to do one day, when I have the right gyro.

Udi-

[PW_Plack]

Gene,

You're on the right track. The so-called "1/4-wave" antenna you reference is, as you supposed, actually a half-wave dipole. They're just using the rubber duck in place of the other half of the dipole to save space. Efficiency will be lower, but the frequency range broader, than for a full-sized dipole.

The full-sized dipole will work nearly as well as a quarter-wave vertical, but if you can't find the room for a quarter-wave whip with a ground plane made from wire, do you really have room for a full-sized half-wave? In some cases the answer will be yes, especially if you're trying to 'glas it into a window pillar, or hide it in some other narrow, vertical space. It might be more useful as a Nav antenna, where horizontal orientation is desireable.

A half-wave antenna can be made to resonate whether it's fed differentially at the center, requiring a balun if fed with coax, or from one end, which typically does not require a balun. The varying shapes all have their roles depending on the amount and the size of the available space. Choose the one which allows you to minimize proximity to metal airframe segments and other conductors.

The so-called "gain" antennas, such as the 5/8-wave, are not magic. They achieve higher radiated power measured at the horizon by redirecting power that normally is radiated straight up or down. In a land mobile application, that's a good deal. In an aircraft, you usually don't want to drastically reduce reception and transmission for aircraft (or airports and nav aids) directly below you.

[rehler]

Paul W. Plack,

Back in April you made a drawing of an antenna with a ground plane made up of two 24" wires sticking out from the antenna base. I have a question? Can the wires stick out at 90 degrees from each other (north and west), rather than 180 degrees?

Due to the room I have available this is all I can do. If it won't work then I will need to buy the other type of antenna that Ken J. uses:
http://www.aircraftspruce.com/catalog/avpages/antennasystems.php

Thanks.

[PW_Plack]

Ken,

A qualified "yes." It will be a huge improvement over no ground plane, but may not provide the perfect 50-ohm match the radio wants to see. It may be slightly directional, more efficient on both receive and transmit in the direction of the line of the two wires.

If mounted clear of obstructions, a quarter-wavelength vertical with four ground radials cut 5% longer than the vertical element, sloping 45 degrees down from level, and oriented at 90-degree intervals can be counted on to come very close to a perfect 50-ohm match. Mounted on a pod near an airframe, all bets are off, and you'll need either sophisticated computer modeling or some cut-and-try to get it right.

Join us at El Mirage. I'm bringing test equipment!

[Jonvee]

Ken,

Contact Jim at RST. You might be able to use some foil strips inside your cabin to make a ground plane. They do alot of radio engineering here for homebuilts.
http://www.rst-engr.com/index.html

[rehler]

Paul and Jonathan - Thanks.

[Shadow]

I put an alululuminium rod in my hollow HS and grounded it to my keel that gave me a ground plane in my keel for a N/S ground plane and the two rods down the centers of my HS for an E/W ground plane. It seems to work pretty good.

[Friendly]

Screw,
Did you resovle your radio noise and what was the solution if you did so?