Making good-quality connections with solder-tag BNC connectors?

[prv]

I have an RG-213 antenna cable which I want to terminate in a box with a connector on the outside. This is at VHF frequencies, probably won't be used for transmission but I don't want to rule it out, and I want to lose as little signal as possible.

I think BNC would be an appropriate connector - I don't need great physical robustness or any waterproofing and I've read that it's better from an RF point of view than the standard PL-259. It's also conveniently more compact and I have various 50Ω BNC patch cables lying around which will be handy.

Specific screw-together connectors for RG213 (relatively chunky) to BNC seem to be few and far between, especially in bulkhead mount form. But there are lots of generic (ie, not specific to a particular size of cable) bulkhead connectors around with a central post and a tag for the screen:

However, the obvious way of assembling these (core soldered into the central cup, braid gathered into a pigtail and soldered to the tag) loses the concentric nature of the screen for the last 10mm or so. The questions for those knowledgable in RF (I know there's a few about) -

• Does this gap make any appreciable difference to the signal?
• If so, is there a special method of assembly that should be used instead?
• Or are these particular connectors just a bit rubbish and there's no way of assembling them without substantial loss?

Cheers,

Pete

 

[habeer]

Consider using a 'N' connector with RG-213, because it's so hard to bend RG-213 and it'll put a lot of torque (could shear off) a BNC connector in a marine environment. N connectors are available in bulkhead style as well. If you must use BNC, you can terminate the RG-213 in N, and use a short piece of RG-58 with N on one end and BNC on the other.

Harold Beer
35 year veteran of radio broadcasting

 

[prv]

Thanks for the suggestion - the RG213 will be emerging through a hole so firmly held in place, and I can freely choose and locate the box so that it's over the hole and the face with the connector is directly opposite the cable and a suitable distance from it. So there should be no strain on the connector, and nothing at this point will be undergoing any movement. My aim is to use as few connectors and adapters as possible.

Pete

 

[William_H]

The losses at VHF frequencies will be negligible so just use what you have in the manner you propose. olewill

 

[Daverw]

N type is really needed if you do end up transmitting, much better electrical connection

 

[Salty John]

Bayonet connectors are most useful if you will be unplugging frequently, they were designed for laboratory purposes such as connections to oscilloscopes, generally with smaller size cables. The threaded version, the TNC, is a better choice if you don't need the convenience of the BNC, it gives a more positive connection.
(Assuming you are not enamoured with the N type.)

 

[Chalker]

N, BNC and TNC are all good connectors and for the perfectionist are better than 'UHF'. Whilst you can measure a difference with lab equipment you are most unlikely to notice a difference in practice.
Why use the solder tag versions when proper coaxial entry types are available?
Salty John is correct, N and TNC re better for installation use rather than quick release. Don't forget a thorough rapping of self-amalgamating tape at all joints inside and outside except for the one to the radio.

 

[lw395]

Those connectors are used a fair amount at frequencies well below vhf.
You can get away with them at hf, if you keep the ground pigtail very short and you don't have lots of other discontinuities or particularly high power.
I don't think they are appropriate for a cable of any length, as the cable will be vulnerable to fatigue at the connections, and open to corrosion, particularly of the braid.
Even an oxide film on the braid can put the loss up a lot, but in a marine environment, wholesale failure of the braid is likely with a few short years.
There are proper clamp and crimp BNC females available for most cable types, which avoid both those problems.

N type is a better connector, but very big.
TNC is not much used, it negates the advantage of being able to buy reasonable quality patch leads easily.

 

[prv]

Why use the solder tag versions when proper coaxial entry types are available?

Do you have a link to one? Bulkhead mounting (to go on the side of a box), RG213 cable. Not silly money, preferably not from China due to the delivery time.

Pete

 

[habeer]

Do you have a link to one? Bulkhead mounting (to go on the side of a box), RG213 cable. Not silly money, preferably not from China due to the delivery time.

Pete

Amphenol 082-97-RFX is a good quality low-cost connector, more than adequate for VHF. I'm not too clear on what's going on in your 'box', sounds like you are interested in receiving, and as low loss as possible (hence RG-213). If you are going to a circuit board, the solder cup connector, with the shield attached to a lug, and bolted works well. If it's a module with a connector, then I'd use a bulkhead mounted between series adapter, and a short jumper. There is a little bit of loss at every connection, transmit or receive, but most times it's worth a short jumper instead a direct connection, especially with large coax. (I remember when I had to repair an antenna with a broken 'N' connector because someone thought connecting 1 5/8" directly to N was a good idea. It would have been much better to have a short jumper with a 1 dB loss than the infinite loss broken connection as thermal expansion and contraction sheared off a $100 unavailable connector)

 

[prv]

Amphenol 082-97-RFX is a good quality low-cost connector, more than adequate for VHF.

That's a solder tag N connector, though. I was asking Chalker about the RG-213 "coaxial entry" BNC bulkhead connector he was advising me to buy, since they seem hard to come by. Not non-existent, but not widely available.

I'm not too clear on what's going on in your 'box', sounds like you are interested in receiving, and as low loss as possible (hence RG-213).

There isn't really anything going on in the box, it's just to give a neater appearance than a cable sticking directly out of a ragged hole. The RG-213 may be overkill for this application; it's good quality cable I had left over from another installation (where it has made a very noticeable difference over the cheap thin stuff previously used) and the other end of it is now mounted somewhere inaccessible so I'm not changing it now

Pete

 

[Chalker]

Do you have a link to one? Bulkhead mounting (to go on the side of a box), RG213 cable. Not silly money, preferably not from China due to the delivery time.

Pete

No link but if you google 'tnc bulhead' (or bnc, N or whatever) you should get hits of RS or Farnell. Lots of options to search; male, female, cable, rg213. Or go straight to either company and use their search/selectors.

Crimp are available but you do need the tools, soldering is good for the centre pins if you have a good pointed iron, check online instructions or probably Utube. The screens are clamped.

 

[forelle541]

Bulgin make an excellent one but it's a bit of a bugger to fit.