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BNC Connection Help

S

szicree

Well Known Member
Well, after much research I decided to mount my Comant bent whip on the centerline about six inches ahead of the spar. Everything looks terrific except for one small problem. The connector is directly underneath the bottom tip of the control stick. Once I get the little 90 degree adapter on there, the clearance between stick and connector is about 3/4 inch. I just don't like the idea of such a non-movable object protruding so close to the bottom of the stick. One option is to relocate the stick and fill the holes (not my first choice). The other is to figure out some sort of low profile wat to attach the antenna cable. I can easily put a small stud on the antenna doubler and connect the sheild with a crimp-on ring terminal, the problem is in finding a way to connect the center conductor. What I'd like best is a way to have a stud coming straight out of the antenna. I'm hoping somebody has a great idea because I really don't want to move my antenna.

Steve Zicree
RV4
 
bnc Connectors

Steve,

Do a web search on BNC connectors, and you'll find a lot of varieties out there. Unfortunately, I had a similar clearance issue with the back of my Garmin 430, and ended up having to make what I needed (but I have some clever technicians at my disposal) from several different connectors. A good, cheap, low-profile right angle connector is what the world needs! I tried to buy the one that you get with the ICOM radio, and they were happy to sell me one - for about a hundred bucks! Airway robbery.....

My experience with direct connections like a ring lug for ground, and then putting the center conductor on the antenna with another ring lug (ala cheap, bent whip antennas) has been very bad - you get more RF energy bouncing around inside the plane than you end up radiating.

Wish I could be of more help - just lettign you know my experiences.

Paul Dye
 
Steve,

Don't bother with relocating the antenna or using that 90 degree adapter/coupler.

We along with other part suppliers stock and sell a right angle crimp BNC connector that is also made by Amp, but they are not cheap (downright outrageous). They crimp together just like regular BNC's, and don't protrude any higher than your regular BNC, but let the coax exit at a 90 degree angle.

I'm sorry, but I think the above method just plain looks kludgy to me.

We routinely use these right angle BNC's for exactly the installation you describe, and I personally did it that way on my RV6 with the bent whip under the seats.

Contact me off list if you have any questions.

Cheers,
Stein.
 
Last edited:
Stein: How outrageous? It's okay, I can take it.

Mark: Dang! That is so brilliant and so simple I'm embarassed I didn't think of it myself.

I'm thinking that a combination of both will get that thing right down against the skin if I want. I feel so happy that I don't have to fill those holes.

Steve Zicree
 
I was dealing with a tight fit when I wanted my Com. antennae dead center on the fuse awhile back.

46393864718050399kc.jpg


46395249718050150cl.jpg


I can't find my pict of my spacer plate. mark
 
.125" thick

thought I posted two hrs ago. I'll try again.

I was thinking of my Garmin 330 antennae but same idea.

I barely cleared with my Com. 90 deg. connector also but no spacer. Sorry about the big picts.


926050282ou.jpg


926050302vs.jpg
 
The spacer is probably not a good idea. The antenna is sized for the correct frequency at 1/4 wavelength (about 3 inches in this case) and needs a metallic ground plane to work correctly.

The spacer has increased the effective length of the antenna by a measurable percentage.

Yes.... I know "it works", but it doesn't work as efficiently as originally designed, or as required in any TSO (I believe the transponder system is one that does have to meet TSO specs. even in our homebuilts)

gil in Tucson
 
az_gila said:
The spacer is probably not a good idea. The antenna is sized for the correct frequency at 1/4 wavelength (about 3 inches in this case) and needs a metallic ground plane to work correctly.

The spacer has increased the effective length of the antenna by a measurable percentage.

Yes.... I know "it works", but it doesn't work as efficiently as originally designed, or as required in any TSO (I believe the transponder system is one that does have to meet TSO specs. even in our homebuilts)

gil in Tucson
Click to expand...
I thought the radiating length of the antenna was measured after the coax termination point not the distance from the tip to the ground plane. Can you enlighten us here with a little more antenna theory and perhaps dispell a little more of the witchcraft surrounding these things?

inquiring minds would like to know...

-mike
 
Gil,

The spacer does not increase the length of the antenna, at all. I assume that the spacer is grounded to the skin, and is part of the gound plane. You can see that there is an insulator (rubber, I assume) between the spacer and the antenna. The spacer only raises the antenna above the ground plane, and by an extremely small amount. Looks like a good fix to me.

Tracy.
 
It's a quarter wave above the ground plane, not the end of the co-ax.

The original picture was of a transponder antenna, right?

A 1/8 spacer at comm. wavelengths (around 23 inches) is negligible... at transponder wavelengths, it's no longer negligible.

The first section of this describes 1/4 wave antennae, the rest gets into 'black magic' :)

http://www.web-ee.com/primers/files/antenna.pdf

gil A
 
For the outrageous amount $17.50 you can save yourself the hassle of fuddling around with spacers, lord knows how much time fabricating the thing, or using ring terminals, et.al. The spacer idea is fine and shows the ingenuity of builders, but once again reminds me of a band aid. Buy the right angle BNC connector and be done with it. No flames intended, and it's just my 2 cents as usual.

Cheers,
Stein.
 
I'm with you Stein, but I'm not really sure the right angle deal will get me the clearance I need. The 90 degree adapter that's on there now looks about the same size as the photos I've seen of 90 degree connectors. I guess I'm not really sure how much clearance I need. I've currently got around 0.5 - 0.75 inches, which is probably plenty. It just bothers me to see that thing sticking up in such a potentially serious spot.

By the way, do you happen to sell the connector pins that go in the back of my TDR 950 tray?

Steve Zicree
 
szicree said:
The spacer is metal and therefore becomes part of the ground plane.

Steve Zicree
Click to expand...

Steve,

No, not at RF frequencies. ... because the spacer is not a quarter wavelength in radius.

Make a spacer that is a disk and a diameter twice the length of the transponder antenna, and then this statement would be true.
The spacer would then become the ground plane.
RF waves are measured to surfaces at this frequency, not just equal electrical potential....

gil A
 
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