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Tiny Radio Connectors

In the past few months I have assembled: an MTR-3b LCD, a ZM-2 tuner (BNC) kit I put together, a Pacific Radio 20/40 antenna kit to assemble, a couple fibreglass masts sitting in the corner, 24 AA Eneloops and a nice charger on its way to me along with a keyer. Now I need to order some BNC’s, battery cases, and some other misc. items to get this up and on the air.

I have some questions before I put in my order. Why use RG174? RG8 is less lossy. Or does the connection between rig and tuner not matter since it is so short? …RG8 too bulky? …same with the height to the top of the mast? …too much weight? I’d think you’d want to squeeze every ounce of electron at low power? …or I’m straining at gnats?

Just thinking out loud and no one to bounce this off of up north here. I’ve never dealt with such tiny coax and connector before.

…do I need a good crimper to do these connectors? …recommendations on BNC’s? …nearest electronic store is 250 mlies away so need to order everything which is the way life is here, you need to make do yourself.

Thanks in advance.


For the length of cable between a radio and tuner, a few 10s of cms, it doesn’t matter. So a light weight cable will do fine. RG-316 is a better thin cable than RG-174. It’s Teflon so doesn’t melt when soldering. And when you are learning to fit the connectors, it will melt!

Buy a bag of cheap connectors and some cheap cable from eBay to practice on. They buy some better connectors for the real thing. In a perfect world, solder the centre pin on 316 and crimp the shield. You need crimp sockets and a crimp tool. Balance the cost of the tool by how many crimps you will make. Some cheap tools are ok as you wont be going into production.

You will find ready made BNC<>BNC RG-316 patch leads on eBay that will meet your needs. Maybe a bit suspect for UHF and upwards as the cheap Chinese connectors may be poor tolerance compared to pricey ‘real’ connectors from Suhner or Radiall or Greenpar or Andrew. But it will be fine for HF and QRP power.

It’s still worth buying some and learning how to fit them…

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:+1: on all Andy’s comments.

Chinese connectors for practice only!

I bought a bag of crimp BNCs and the centre pins looked like they were for something else entirely!

A crimp tool can be had pretty cheap.

The down side of RG316 is it says how you reel it up. Even meticulously coiling over-hand then under-hand it still wants to go its own way, due I guess to the copperweld inner. :slight_smile:

My normal coax is RG58 Polyurethane jacketed coax. Stays flexible in cold temps, still good at -28C last January. I use the same style of coax but RG174 for shorter runs.
Connector wise, from Mouser is the best deal here. However I do like the ones Sotabeams sells but the shipping is a killer. Crimpers, look at B&E or MRO in Calgary.
If needed I will go shopping for you. Trust me me buddy :wink:


I dont go out to the mountaintops to do radio. Mine is at all the local parks. After using the MTR3b with an RCA phono plug for antenna connection, I changed all my connectors to RCA.
Super easy to solder to my coax, easy to plug in and out and I can just stick the wire into the jack if something get broken.
Last big plus for me is that I can get them for 10 cents a piece at the local electronic surplus store. The jacks are more- 35 cents each.


Not all RG174 is the same. DXW174 from DXWire is made to their own spec (solid copper inner conductor) and is vastly superior to normal RG174:

It is reasonably priced as well. I like to crimp my connectors where possible, so a multi-crimp tool set is very handy. Our club in Graz has one, so everyone can borrow it whenever they need to. Perhaps there is a club near you that has one?
73 de TF/OE6FEG/P

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This has all been very helpful. Yes, thank you to everyone.

I went ahead and ordered a cheap crimper along with a handful of BNC’s and will put several together on 174 per your suggestions. Also got a length of 58. 316 was not so easily had and I will keep watch for some; shipping any more is the main drawback. I will have to ask about better crimpers from our club but it might not be had. No one at the meeting two Saturday’s ago fabricated BNC cables. Considering our central meeting point is 200 kilometres away it is something to plan out beforehand. :wink:

I hadn’t seen any posts on this before and I certainly had no need for this using standard HF gear. Just another part of working up a SOTA station. I journey on. Later…

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to your question, if the feedline is very short (six feet) and/or being used on low frequencies (40 meters) it isn’t an issue. The higher the frequency, the longer the cable, the greater the loss. Everything between the TX and the antenna contributes loss, including the tuner.

If you use a dipole in an inverted vee, the feedline must run up the pole to the peak, now the pole has to be so much heavier to deal with that, everything decays quickly…

I use no feedline, and only what amounts to an impedance transformer. I plug the impedance transformer directly into the radio, and the end of the resonant endfed halfwave wire directly into that, no feedline. There is very little RF radiation near the end of the EFHW so I use the wire itself for feeding. At the same time that I have reduced overall loss, I have reduced weight, volume, and complexity. I also changed out the BNC connector to an RCA. ( BNC’s are stressful on thin coax).

I hold the radio in my hand, 3x5 card clipped to the back of the MTR for logging. Keyer is built in. I added a tiny touch paddle board, inside the MTR, with just posts to touch sticking out, no contacts to get dirty, no moving parts to be damaged in transit.

73 fred kt5x (aka WS0TA)

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Hi Craig,

I’d just like to answer some of your original questions.

Most of us use telescoping fibre glass masts (squid poles) and discard the thinnest top section. Even so the mast will not hold up RG213 so we don’t use that. Even RG58 is going to induce some serious bending and needs taping to the mast for at least the top half. So that’s no so common.

Most of the ops I know use RG174 or 300 ohm ribbon for feeding doublets. I’m not a fan of end fed wires because often their implementation is lossy. In VK we need to cover out to 3,000 km for local contacts so every mW needs to be radiated.

Yes the 8 m or more of RG174 as required with most masts has some loss on the higher HF bands but that’s acceptably low and the ability to wind it up (fig 8 over and under) without difficulty is a bonus.

Small connectors, SMA for example, are popular but I use PL239 style connectors because they are rugged and easy to solder with the right soldering iron. I pack the plug exit point with Silastic type filler and that not only keeps water out, it stops cable tension having any effect on the soldered connections.

All my connector failures with SOTA have been with BNC connectors. When I have to use them I go for crimped braid and soldered pin. Lots of sage advice here on that.

One problem with PL259 plugs is the thread and the length of thread. Some SO239 sockets do not have a long enough thread and the plug is still loose when screwed home. And Yaesu once used their own thread which was a great irritation. Some insulation in the plug is a low temperature thermoplastic. Use connectors with teflon or the brown insulation.

RCA connectors can be used on HF but there are variations in size and some cheapies will damage the real ones. That said I still have one on my MTR transceiver but I use a short adaptor cable.

Don’t worry about having your first set up having to be perfect. You will still have fun and will learn as you go.


Fear not Ron of the humble EFHW. A fortnight ago using a homebrew EFHW from VK1/AC-028 Billy Range I worked stations in VK1, VK2, VK3, VK4, VK5 and ZL all at 5 watts voice mode SSB in the 40 and 20 bands.

All connectors from the impedance transformer to the transciever are crimp BNCs on RG316. :slight_smile:

73 Andrew VK1AD

Another excellent blog entry Andrew… simple and elegant presentation with photos that are focussed and clear with easy to read diagrams.

Thanks for the info on that cable. To be pendantic it’s not RG174 but 174 sized. It’s got the same loss as LMR100, another 174 sized cable. Still worth investigating next time I need to buy some more 174 sized cable. I picked up 12m of RD316 (aka RG316D aka RG316 double screened) for €10 at FN this year. If I’d have known of the DXW wire I’d have bought that instead as DX Wire had a stand at the rally. The DXW174 price looks excellent even when considering shipping costs.

I just don’t like them Ron. At these frequencies and powers there’s nothing wrong with them other than they’re big and heavy compared with many other connectors. And personally, I think fitting them is a pain. SMA are wonderful but they are such a nightmare to connect when it’s cold and you have big old podgy bear-sized paws like me especially when you have some thicker more microwave compatible cable that has a mind of its own with regards to handling (I’m thinking of you RG-400!). There’s nothing wrong with RCA plugs at these freqs and powers but unless you modify all your equipment to sport them or it’s all homebrew you end up needing adapters.

The important point I suppose is that at QRP HF levels the connector is not that important but it’s best to pick something and standardise on it. Although sometimes you’re forced into some compromise… I have VHF/UHF and microwave gear that uses SMA and everything else in BNC. I do carry the “FMFuniversal-cable” with me. This is a 1m length of quality RG58 sporting a cable mount female BNC at one end and an RG58 style SMA male at the other. Combined with an SMA female to BNC male adapter I can cross connect all the different antennas to all the different radios used for SOTA though why I’d want to connect the 80m dipole to the 13cms transverter is questionable but it can be done!

Just one thing I’ve found with connectors: the right angle BNCs for RG174 are a little delicate where the dielectric enters the main body. I broke one once just by dropping it, and they are not cheap to replace, well, the Telegärtner ones aren’t. It was also pointed out to me that cheap connectors (in particular but not restricted to RCA) may have a simple plastic dielectric that could fail at higher output power. Not an issue at QRP, and I have no idea if it’s true or not, but I always go for a high quality PTFE dielectric where possible. After all, I may want to use the lead for something else; field day perhaps.
73 de TF/OE6FEG/P

Hi Craig,
I have been using RG178 since the 1980’s. It’s PTFE, high quality and I can’t find anything lighter or thinner (1.8mm). I also use RG316. The loss figures are not significantly different from RG58 at HF though the lines are diverging more at VHF.

I used to use solder type RG58 size BNC’s for these cables and it was necessary to build up with heat-shrink sleeving to make them fit but I now use crimp - much quicker. I do use the cheapest crimped BNC’s that I can find and have no complaints (apart from the occasional bayonet being badly machined or in one case completely absent), admittedly mostly for HF but some for 2m also.

As Andy stated, for short lengths, patch leads etc, loss is not a consideration but it’s worth checking that you’re buying 50 Ohm and not 75 Ohm, thought that can be next to impossible the way that many of the products are presented. Often the sellers don’t know much about what they’re selling.

I agree about SMA’s in cold weather or if you’re a ‘blacksmith’ and not a ‘seamstress!’

Yes, me too! I have wondered about using some spinner grips like these:

I haven’t tried them, I guess they could be more trouble than they are worth in the field, unless they stay put reliably. Care needed not to over tighten the connectors too…


Wow Adrian, I’m impressed. How on earth did you find something that obscure and unexpected. They could be useful in certain circumstances for sure. I have SMA to BNC adaptors on my VHF handhelds, which annoyingly are a bit contrary in not being able to agree on whether they’re male or female. I haven’t arrived at a summit with the wrong gender yet but no doubt it will happen!
73, John.

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Hi Andrew,

You are now running an OCF dipole with links, not an end fed wire so I would expect reasonable performance. VK1 and VK2 is very short haul from that summit anyway. ZL is more like it. If it does what you want stick with it.


Well, I just thought they would be a good idea, and whenever I have a good idea I can be sure that someone cleverer than me has already thought of it, so I googled :smile:

Curiously, I just came across these whilst looking for something else, which could be good for anyone with a 3D printer:

They are on this website: http://www.hybridpretender.nl/ towards the bottom of the page.

Yes, I have hand held radios with different gender SMAs which can be a nuisance. One of the cheap adaptors that I use fell appart, and has been soldered back together - so I can recognise that one without finding my specs and peering down the end!


Hi Craig,

Re the different types of “UHF” connectors, the M series from Japan is almost the same as the UHF but sufficiently different that some genuine Amphenol PL259 plugs won’t mate with a type M socket, due to a slight pitch difference in the outer thread. The “UHF” series was so named a long time ago, when anything above 30 MHz was regarded as UHF, but it is far from a valid name now even though the name has stuck. They are non constant impedance, take time to connect and disconnect and are bulky. Some types require soldering of the connector to the braid, which often results in melting of the inner insulation and if the user is not experienced enough in preventing it, can actually result in a shorted cable as the inner conductor moves over towards the braid within the melted insulation. The PL259/SO239 connectors on most ham radio equipment are there because they are cheap and most people can use them, with or without adaptors to other more convenient connectors. Where possible I substitute a BNC socket.

For SOTA use all the way up to 1296 MHz I use BNC connectors and RG58 sized cable. Short lengths are not sufficiently lossy to justify anything of higher quality though there are some similar sized (eg. LMR) cables that have lower losses. Whether the improvement in transmitted power or receiver sensitivity is actually worth while is something each operator needs to decide. 1 db cannot usually be noticed. 10 db can be noticed especially on vhf/uhf receiver sensitivity. The feedline lengths required for SOTA are not sufficient to justify lower loss cables for HF and VHF in my view. UHF - if I am trying for a distance that could be marginal I will improve the cable.

The SMA series was complicated by the wifi industry deciding to create a reverse polarity version, where the plug contains a socket and the socket contains a plug. This was intended to make it difficult for people to use existing connectors, antennas etc, but pretty stupid given the ability of high volume manufacturers to make adaptors which are readily available from the auction sites. I think though, you are referring to radios being either a male or female connector, which complicates the requirements for antennas, amplifiers, etc. I think you are doing the right thing by checking out the connectors required by your gear and making sure you have the right cables in the backpack when you need them. I carry a small plastic box with several compartments, with PL259-BNC, BNC-BNC (MM and FF) and stereo 6.5-3.5mm adaptors (needed for one of my radios that has a 6.5mm socket for the key). It adds a bit of weight but has saved a few activations from failure.

Edit: adding a comment about RCA (phono) connectors. The original design of these was a simple 50 ohm connector apparently rated up to the gigahertz region, which is why Collins and Heathkit gear used (ceramic insulated) versions of these on their radios. It wasn’t due to being cheap, it was because when correctly manufactured and terminated it is a good RF connector that is very easy to connect and disconnect, unlike the poor old PL259 series.

73 Andrew VK1DA/VK2UH

Hi Andrew,

You might have added that anyone on UHF looking for weak signals should be using type N connectors and RG8 sized foam dielectric coax. Crimp them. Use a ratchet crimper unless you are very strong gripped.

Someone asked about tightening and undoing coax connectors. Those plastic spinners would be good if they could grip round connectors. :joy:

Please don’t use image


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