BNC Connectors

[Knighty]

Hello Forum members

 

Can anyone give me a diagram/info on the proper instalation technique of the screw in type that is used for our VHF radios. Dick Smith's supply them by the bucket loads but cant give me any information other than the price.

 

Thanks

 

Knighty

 

 

[hiperlight]

Knighty

 

Look up Dick Smiths Annual Catalogue 2005/2006 page 351 or google 'wiring rf plugs' and download the 56 page CASA document on 'RF Connectors and Cabling' at:

 

www.casa.gov.au/rules/1998casr/021/021c99s2c12.pdf

 

Bruce

 

 

[Wilfred]

I would reccommend getting someone like you Local radio or communications tech to fit a crimp type one with the correct tools.

 

The solderable (if thats a word) type that you get from DS will not be as efficient as the crimp type and you do need the right crimping tool. Your local tech would not charge much to fit one.

 

 

[Ross]

Hi Knighty

 

See attached jpg file. More readable as is now four files.

 

 

 

 

 

 

[Knighty]

Thanks for the info guys, I will be right from here. Ross, you have won this round as your thumbnail explains the go in plain English and Microair demonstrates the same connection as the ones DS supplied me with.

 

Safe flying fellas.

 

Knighty

 

 

[Dieselten]

I second the recommendation to use the crimp-on BNC connectors. I have put literally hundred of these on both 50-Ohm radio cable and 75-Ohm TV cable. The screw-on variety are a PITA and will let you down with poor performance almost from day one. Typically people pull them off the end of the cable and just push them right back on again and expect them to work. They do - sort of - due largely to capacitive coupling, but they are very poor compared to crimp-on BNCs. The centre-pins are especially prone to coming adrift.

 

The BNC is a very good connector with a wide frequency range and substantially constant impedance throughout these frequencies. Using a cheap one to save a few cents is false economy. Using a decent one saves all sorts of radio problems, especially poor receive performance (on receive, microvolts are induced at the antenna terminal, and any deficiency in the connector will manifest itself as noisy reception or no reception at all.) Practically anything will transmit (over a limited range), even a 50-Ohm resistor (such a device is called an "artifical antenna" or a "dummy-load"), but receive is where you really learn how good your installation, cable and antenna system are.

 

Use crimp-on BNCs and get a competent person to install them. Take the screw-in ones and throw them into the nearest lake, ocean or bottomless pit.

 

Incidentally, the BNC stands for Bayonet Neil Concelman, and not British Naval Connector, as is popularly believed.

 

A variation of the BNC is the TNC, where the outer section of the male connector (the one with the pin in the centre) has a screw-thread rather than a bayonet fitting. Some handheld radios use TNC (GME ELEctrophone UHF handhelds for example,) but they are not commonly encountered in aviation VHF units.

 

Also, for best radio transmision and reception, make sure the antenna is resonant and mounted as high on the aircraft as possible, with a decent ground-plane if at all possible, and impedance matched to the output inmpedance of the transmitter (nominally 50-Ohms). A slight impedance mismatch is acceptable because we are not continuous duty-cycle radio transmitters. Use high-quality coaxial cable (preferably with a MIL-spec number on it) and eschew cables with no brand or identifiication at all...they are cheap junk. As a rule, the more braid the cable has the higher the quality.

 

If your radio receives poorly, suspect bad connectors before just about anything else. Chances are you'll be correct.

 

 

[eastmeg2]

I have to disagree about the screw-on type of connectors being a PITA. Yes they do require some extra care to instal, but anyone with a pair of wire cutters, precision screw driver set and a delicate touch can make these perform just as well as the crimp on version, without having to go the the expense of buying the right crimping tool or geeting a professional to do it.

 

I have forgotten to disconnect the coax cable between my wing and trike base a couple of times when de-rigging in the past and the screw-on type is far easier to repair after these little mishaps.

 

What you do need to know is exactly how far you should be trimming back each of the dielectric, outer conductor and outer insulation in order to make the connector work properly. A little bit of knowledge goes a long way - and weighs nothing.

 

Cheers,

 

Glen

 

 

[numptie]

May as well throw in my two bob's worth. In my experience (23 years of electronics and communications) I'd have to say the best way to go for performance is the BNC with the solder on pin. Unfortunately they can be a bit of a pain, a little fiddly and, as Glen mentioned, you have to make sure the insulation and dielectric are stripped back the correct amount. Luckily, Dick Smith electronics (and a number of others like Jaycar, but DSE is probably cheapest) sell coax strippers for about $20 and they'll do RG58, RG59 and a few others.

 

Getting the crimp on type doesn't get around the requirement to strip the correct amount. It does make putting the connector on a little easier though because there's no soldering or screwing. You can buy a crimp tool (again at DSE or many other places) and a cheap one that will "do the job" is around $40.

 

Whichever connector you get, make sure you prepare the cable properly, strip it back the right amount and make sure the cable is the right length. If it's for a radio antenna and it's not the right length, in extreme cases it can create standing waves which is not good for the output of the radio.

 

The other option Knighty is to send it to me, I have all of the tools for the job sitting right here at home.

 

Bob