# Antennas

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#### Spaceclam

##### Member
Hello,
I have a New-to-me flybaby that was fitted years ago with a whip antenna mounted behind the headrest, and connects to a hand held radio. This airplane is about 30 years old, and one of its issues is radio noise. I have to keep the squelch all the way up, and sometimes it causes me to miss transmissions. It’s not engine noise. It’s more like aliens screaming in my head, and the noise is far louder than the transmission level. The radio works just fine by itself, but there isn’t really much room in the cockpit to use the handheld radio antenna and I like my radio mounted as it is

Seeing as there is corrosion at the base of the antenna and the connector is visibly discolored, I’d like to just replace it all and see if it helps. In looking at antennas, there appear to be nearly identical models ranging from $75 to$1500+. Is there some compatibility issue I am not aware of? Does it need to be sized to work with the lower-power handheld unit? What should I buy?

-Clam

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#### Pops

##### Well-Known Member
HBA Supporter
Log Member
Been using these antenna's since the article in Sport Aviation. They work great, low cost, light weight and no drag.

#### Rhino

##### Well-Known Member
Is this noise all the time, during all received transmissions, or only when you key the mike? If it's the latter, it may be a simple matter of the external antenna being too close to the radio. Fortunately you can put an antenna anywhere in a Fly Baby. It doesn't need to be externally mounted, because the wood/fabric construction won't affect your signal. I would try something as cheap and simple as this, just to test the possibilities:

#### Spaceclam

##### Member
Is this noise all the time, during all received transmissions, or only when you key the mike? If it's the latter, it may be a simple matter of the external antenna being too close to the radio. Fortunately you can put an antenna anywhere in a Fly Baby. It doesn't need to be externally mounted, because the wood/fabric construction won't affect your signal. I would try something as cheap and simple as this, just to test the possibilities:

The noise is not when the mic is keyed. It just happens randomly, even when the engine is off. I’ll give one of those a try. Also, any thoughts/comments/suggestions on the connector and wire? How long can the wire be? Do they make 90degree connectors so it doesn’t put so much strain on it?

Thanks,
-Clam

#### rv7charlie

##### Well-Known Member
If it's breaking squelch with no transmissions in the area, then either there's something wrong with the radio or you've got excessive RF or electrical noise in the a/c.

If it were me, before spending money I'd try to find the source of the problem. Things to look for/think about:
If it's an ancient engine, are the mags & plug wires shielded?
Are your P-leads properly shielded and terminated? (Whole chapter there...)
Is there a generator/alternator? If so, does turning it off improve things?
Is the shield on the antenna coax properly terminated *on both ends*?
Is the antenna grounded properly to the airframe?
Not directly related to a noise problem, but does the antenna have a ground plane? (doubtful if it's on the fuselage top behind the headrest)

Just a few things that came to mind in the time it took to type them.

#### Spaceclam

##### Member
I probably should have mentioned -this aircraft has no electrical system. So given the noise when the engine is off... that pretty much rules everything out besides antenna and connections. I think?

#### rv7charlie

##### Well-Known Member
A comm antenna can be as simple as stripping about 22" of shield off a piece of coax, and attaching 3 or 4 22" long radial arms attached to the shield at the strip point: 1/4 wave antenna Now it it will only be maximally efficient at one frequency, but it will 'work'.

If the radio is breaking squelch without the engine running and in receive mode (not transmitting), and there's no electrical system, it's hard to understand where the noise is coming from, except from the radio itself. Does it have the problem on multiple frequencies, or just your local active frequency? Are you doing the test out in the open, well away from a hangar or other building that might have fluorescent or LED lights, or other noise generators? The fluorescent lights in my hangar drive my handheld crazy, unless I get 20-30 feet away from them and outside the hangar. Have you verified the integrity of the coax, from the connector at the radio end to the connector at the antenna? Is the noise the typical 'white noise' that you hear from any comm radio when you disable the squelch, of does it have any different characteristics? 'aliens screaming in my head' does not sound like normal open squelch. If you're getting a howling or squealing sound, that almost sounds like it's interacting with another radio that's transmitting; the sound you get when one pilot 'steps on' another's transmission.

Kinda hard to 'remote troubleshoot'; just trying to give you some ideas on things to check.

#### Rhino

##### Well-Known Member
The noise is not when the mic is keyed. It just happens randomly, even when the engine is off. I’ll give one of those a try. Also, any thoughts/comments/suggestions on the connector and wire? How long can the wire be? Do they make 90degree connectors so it doesn’t put so much strain on it?
Have you tried a different radio? Maybe borrow one from a friend? It'd be a shame to mess with wiring if the radio is the problem. From what you're saying though, replacing the antenna/wiring is probably a good idea either way. Make sure it's a 50 ohm cable. TV antenna cables can look identical, but they aren't 50 ohm, which is what you should use for the aircraft band. Make sure you have good ground connections at both ends if you fabricate your own cable. Normally you'd make the cable run as short as practical, but don't go overboard trying to save every inch. Prepackaged antenna/cable combinations might be longer than you need, but they're probably acceptable for your application, especially since you have no electrical system.

Might I also suggest you get a copy of Bob Nuckolls' Aeroelectic Connection if you can? Much of it won't apply to you since you don't have an electrical system, but it's still a great reference book to have. Much of it applies to vehicles other than airplanes too.

EDIT: This isn't bad to have either:

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#### Rhino

##### Well-Known Member
Oh, and the specific cable type depends on the application. RG 400 is fantastic antenna cable, but it would be incredible overkill for what you're doing. RG 142 is good, but RG 58 will probably do you just fine.

#### akwrencher

##### Well-Known Member
HBA Supporter
There is currently a good series of articles in Kitplanes magazine on antennas.

#### Rhino

##### Well-Known Member
There is currently a good series of articles in Kitplanes magazine on antennas.
Don't spoil it for me. I'm not caught up on my reading!

#### Map

##### Well-Known Member
I still have a few pieces of RG-400 antenna cable for sale, 17 & 16 ft pieces no connector, and 1 x 17 ft with TNC connectors, $1.10 per ft &$8 for cable with connectors.

#### Bill-Higdon

##### Well-Known Member
What make & model of radio?

#### tallank

##### Well-Known Member
Hello,
I have a New-to-me flybaby that was fitted years ago with a whip antenna mounted behind the headrest, and connects to a hand held radio. This airplane is about 30 years old, and one of its issues is radio noise. I have to keep the squelch all the way up, and sometimes it causes me to miss transmissions. It’s not engine noise. It’s more like aliens screaming in my head, and the noise is far louder than the transmission level. The radio works just fine by itself, but there isn’t really much room in the cockpit to use the handheld radio antenna and I like my radio mounted as it is

Seeing as there is corrosion at the base of the antenna and the connector is visibly discolored, I’d like to just replace it all and see if it helps. In looking at antennas, there appear to be nearly identical models ranging from $75 to$1500+. Is there some compatibility issue I am not aware of? Does it need to be sized to work with the lower-power handheld unit? What should I buy?