RG58 without BNC connector

[PurpleSwamper]

I purchased 2 inexpensive antennas from Aircraft Spruce - one for a Garmin GTX327 transponder and the other for an Icom 210 COM radio. These antennas are nothing more than stainless steel rods with delrin insulators for mounts. They didn't come with BNC connectors and according to the manufacturer (Freeway Enterprises), one attaches the core wire of the RG58 cable to the antenna by wrapping it around the rod and tightening down the washer and nut. There is no connection on the antenna for the grounding braid of the cable and so it attached to the metal fuselage.

In my computer life I've only ever terminated coax with BNC connectors. This is the first antenna wiring I've done. Is this a good practice to attach the cable to the antenna with a BNC? Does it degrade the signal? At the very least shouldn't one crimp on an eyelet connector? How do other antennas attach to RG58?

[PurpleSwamper]

I meant to say.... "without a BNC"

Is this a good practice to attach the cable to the antenna withOUT a BNC?

[bird]

That is different, I would use a bnc connector, my transponder ant. Has a connector on it. I think o e would have more loss without a connector.

Bird

[Walt]

I would recommend you return them and purchase 2 real antennas, they quit using those about 30 years ago. If you are really desperate, you could use one on the com but you definately should not use this style for the transponder (not approved and will never pass the xpdr test).

FYI: the center conductor goes the the antenna terminal and the shield is attached to the antenna ground plane using a screw/bolt.

[SteinAir]

Walt beat me to it!

Do yourself a favor and just don't use those antennas. They are NOT good antennas for a whole host of reasons (bad for RV speeds, bad for antenna performance, etc..). Those antennas are best used on something like a Cub/Champ/Stearman (and even then barely). Overall they are a POOR choice for an antenna and to be my usual blunt self: this definately is one of those times where that selection is pennywise and pound foolish. As long as you're at it I'd also recommend ditching the RG58 and just putting in RG400 while you're working on it.

Just my 2 cents as usual!

Cheers,
Stein

[rleffler]

I agree with Stein and Walt.....

If you want some good antennas and save a little money for ones not certified, check out:

http://www.deltapopaviation.com/Home.html

Also, like Stein mentioned, go with RG400.

Pay attention to your connectors. Most are BNC, but Garmin does use TNC connectors on some devices. Also, you need to ensure that the connector is good for the wire you use. The white insulator comes in different thickness, so they aren't always swappable.

Since your new to all this, just go to steinair.com and get the connectors and the appropriate crimp tool. Stein's inexpensive crimp tool works just fine.

[PurpleSwamper]

Thanks for your suggestions but I'm not looking to switch out the antennas or cable... I'm just wondering what degradation if any would be experienced connecting the RG58 to the antenna without a BNC style connector.

My cable lengths are under 20' so I'm expecting RG58 will suffice. I think RG58 vs RG400 has been debated under another topic so will leave it alone here.

Walt: why do you say these won't pass the transponder test? One of the 2 antennas is afterall a transponder antenna currently sold by Aircraft Spruce.

Stein: Can you give me a more technical reason as to why it's a "Poor choice".

I guess I wasn't looking so much for sales-type advice as I was a technical evaluation of the degregation (if any) of using a non-bnc connector to attach the cable to the antenna. There is nothing magical about the BNCs and in the hundreds of BNC cables that I've encountered / installed / troubleshooted, I've found some good and some bad connections.

I suspect the "real antennas" that you speak of are nothing more than a steel rod like these ones, with a BNC connector soldered to the end and piece of fancy looking fiberglass hiding the functional part of the antenna. Am I wrong?

[SteinAir]

Originally Posted by PurpleSwamper

Stein: Can you give me a more technical reason as to why it's a "Poor choice".

Poor SWR, poor attenuation, made for planes that go less than 100kts, not robust, terrible performance, almost impossible to keep secured on an RV, ungainly, big, they bend airframe skins skin without huge doublers, unreliable, not recomennded by any avionics mfgr for decades, not used by reputable installers for decades, not installed on OEM airplanes for decades, they bend easy when a dog runs into them, others in the air trying to communicate with you will be unhappy with your whale songs, poor mechanical installation, poor electrical installation, poor electrical connectivity, poor reception, poor transmission,...and they are of poor quality not to mention they are ugly!

Last but not least - because Walt said so!

I suspect the "real antennas" that you speak of are nothing more than a steel rod like these ones, with a BNC connector soldered to the end and piece of fancy looking fiberglass hiding the functional part of the antenna. Am I wrong?

YES, you are wrong and your suspicions are incorrect. There are thousands of pages of technical details all over google which you can read about the bits/bytes. In the end, it's crazy for you to worry about degradation of using a BNC or not when the antennas you're starting with are only 20% usable to begin with....as pointed out by a few folks that know this stuff. Nobody is trying to sell you anything other than some free advice. Lastly, just because something is in a catalog and is cheap doesn't make it a good match for modern radios in a modern plane. Talk about someone trying to sell you something; apparently someone already did!

Just my 2 cents as usual.

Cheers,
Stein

[Neal@F14]

"Real" comm antennas have a gamma match circuit embedded in the base and will transmit/receive so much better. I removed a homemade copper foil adhesive strip comm antenna from the windshield of my RV-6 that the original builder installed, and replaced it with a RA Miller (RAMI) AV-17 belly-mount bent whip antenna and gained over 50 more miles of useful comm range! Yeah it cost me about $150 but was well worth it. If you're wanting to save a small bit of money, you can get by with using the cheaper RG-58 coax on the VHF comm radio antenna if the length is short (under 12 feet), but I'd still recommend using the RG-400 coax for the transponder antenna no matter the length.

[BobTurner]

As soon as you split the coax into the center conductor and a separate twisted braid pig tail, you lose the 50 ohm impedance geometry. This will cause some of that transponder signal to reflect back into the transponder, which means less power to the antenna. If bad enough you won't meet the radiated signal strength requirement, as Walt was alluding to. This little section of wire will also radiate some power, but it is inside the plane, where all it can do is cause RF interference with other avionics. Oh, and make the inside of your airplane like being inside a low power microwave oven. How bad this short wire section is scales like its length compared to the wavelength. So for the com, an inch or two compared to the wavelength of 10 feet isn't too bad. For the transponder, an inch or two compared to the wavelength of 12 inches is not so great.
A good antenna will not just have a BNC; inside the fiberglass the BNC will have a tapered conductor which expands up to the antenna diameter, and around that there will be a tapered shield, looking like a funnel, which maintains the 50 ohm impedance right up to the antenna, to maximize power transfer.
A good connector is gold or silver plated. I'll bet that if you come back in 3 years and look at a copper wire clamped to steel bolt connection it will be badly tarnished and not a great connection.
RG 58 is okay for the com, but again will cost you expensive watts at the transponder frequency.