BNC Connectors for Transducer Wiring

[Stu Jackson]

The connector between my speedo transducer's 10 foot wire and the long wire back to the cockpit display has 'died' from being "hidden" and underwater in the bilge for the past 29 years.

It is a BNC connector. Datamarine SX120. I have been attempting to get the two parts part for the past few days, using all the "usual suspects" to no avail.

It appears that I will need to cut both wires and install new connectors.

I am aware that there are BNC connector tools available, although the ones on Radio Shack's website have gotten poor reviews.

I will contact DMI tomorrow to determine if it is a 50 or 75 ohm connector and what the wire size is.

I would appreciate any suggestions for a proper BNC connector tool and source that actually works.

 

[chuckwayne]

Stu,
any good electronics or ham store should have what you need - google bnc connectors and you should find several online

 

[Mark Maulden]

Stu, you should be able to get a solder version of the connector. BNC is typically a 50 ohm connector normally used for RG-58 size coax. Thats probably about the size used in the DM installation. When you get it sorted out, wrap the entire connector assembly with "coax seal" and knead the wraps until it all amalgamates. This stuff is used by all the commercial RF installers and hams. You might find it in some electronic/ham stores in your area. I had to order it online and the shipping was more expensive than the product. Sort of looks and feels like butyl tape. BTW, i talked with Maine about Butyl tape and his feeling was it probably would not amalgamate well. You'll never have this problem again......

 

[duality]

stu,

we use "bnc" all the time in the security business all the time for cameras
call adi (650) 871-2300 and see if they have what you need, they may not
sell to you without an account, if so pm me and you can use my account

mike

 

[Stu Jackson]

Thanks for the ideas. The ham outlet here is right next to West Marine!!!How could I forget??? Thanks to your ideas my wife reminded me where it is. Doh!

 

[Forrest15112]

You can definitely use the butyl tape Maine Sail sells. just wrap it in electrical tape. In fact, that's how RF connectors are typically wrapped for weatherproofing. The butyl, especially the black kind used on connectors, will stick to the connector and can be messy. What many do is first wrap the completed and connected junction in electrical tape, wrap that in butyl, then wrap the butyl in more electrical tape. when done, the cable will look like a snake that has just eaten something. I have seen this hold up in sun/rain for many years. There are other products that would work well and not as messy. I have been using self fusing silicone tape made by 3M and like the properties of it. It doesn't leave any sticky residue and seems to hold up well exposed. I still wrap it with electrical tape on my connections just to protect the soft silicone material.

 

[Ken Cross]

I've had good luck over the years with www.digikey.com
Commercial electronics parts supplier.

No connection to them except a customer on occasion.
Ken

 

[Fred Villiard]

Hi Stu,

Pasternack.com is a good place for all styles of rf connectors anr tools.

Are you sure that the cable its self is good? BNCs are relitively robust in damp conditions, the cable can wick moisture and become lossey.

I've done thousands of enviromental lab tests of all types of rf connectors and cable during my time at Amphenol. If it were me I woulld replace both the cable and the connectors, the connectors can not be reused unless they are the solder type.

 

[Stu Jackson]

Are you sure that the cable its self is good? BNCs are relitively robust in damp conditions, the cable can wick moisture and become lossey.

Fred, I can't check the cable condition (per DMI's easy test method) since I can't get the fittings apart! Like I said, I didn't even know a connector existed until the signal stopped, so I found out about it in the DMI FAQs!!!

Here's the latest:

I stopped in a ham radio place at the suggestion of you great helpful folks. It's RG 58 cable. He gave me a male BNC connector for free, but did not have female BNC's, since I guess those are always at the back of the radios and not on the ends of the wire in the "ham radio world." This is consistent with the DMI instructions (for a new transducer with the female at the end of the transducer cable):

When you remove the old SX-120 you will find it is wired exactly the same as the new one, meaning there will be the same 10' cable with a female BNC on the end. There is an interconnect cable between your knotmeter and speed sensor [SX-120]. The interconnect cable consist of a 30' run of coax cable with male BNC connectors on each end. One end mates with your knotmeter, the other end mates with the SX-120. No splicing, adapters or cutting needed. Just disconnect the old one, connect the new one and you are done.

I went to the marine electronic store at the suggestion of the ham radio gentleman, and the folks there said just splice it by un-braiding the outer wire, like the photo below (from wikipedia).

It seems easier than buying a once-in-a-lifetime use tool. I think I'll be splicing.

It's going to be brain-salad-surgery to do this with the wires on the saloon sole.

 

[Fred Villiard]

Stu, you can get a properly made up cable from pasternack, you are asking for cable moisture problems doing a splice. Buying a premade cable isn't the cheapest way but is the best. A 10 foot RG-58 BNC male to male is p/n PE3067-120 $31.39. If you truly have females they have them also and they ship the same day.

 

[Mark Maulden]

I definately would not splice. You can change the setup to have both males and put a barrel connector betwen them. Then wrap it

 

[Stu Jackson]

Re: BNC Connectors for Transducer Wiring-Update

Fred & Mark,

You're right, thanks.

If you're interested, here is the ongoing story:

http://c34.org/bbs/index.php/topic,8467.0.html

I'll keep posting there rather than here, so if anyone searches for BNC here,they'll find it.

Thanks again for giving me those ideas.

Having a reputable local source is also good, in addition to internet-by-mail stuff.

Heck, Berkeley is good for something besides you-know-what.

 

[Stu Jackson]

All done and it works.

Thanks to all of you. Details in the link posted.

 

[pateco]

Another easy option is to make or buy premade RG6 jumper cable of the correct length, and use F to BNC adapters

 

[Ken Cross]

Don't use RG6 for this!!!

Another easy option is to make or buy premade RG6 jumper cable of the correct length, and use F to BNC adapters

RG6 is 75 ohm cable. RG52 and B&C connectors are 52 ohms of characteristic impedance. Depending on application the impedance mismatch can completly kill the signal. Generally higher frequencies become more sensitive to impedance, but it can be easily measured aven at audio frequencies. Always match the cable impedance to the appliances.

I see he already has it solved, but this post is for anyone else contemplating the change.

Ken