Connectors… BNC, N, TNC, UHF, SMA… what?

OK, so everyone has their favorite type and installation method for RF connectors.  While I’m not going to address everything, I’m going to describe my setup a bit, and the rationale I used for my decision.

 

First off, I realize most equipment ships with UHF (or PL-259/SO-239) connectors.  I don’t particularly care for these connectors, as installation is, in my opinion, a pain in the butt.  I don’t particularly care for the amount of heat I need to put into the connector to solder it – I’ve burned myself too many times, and I’ve had too many instances of solder keeping the locking ring from properly threading onto the connector.  Admittedly, NM0X informed me that taking a file or some sandpaper to the connector before soldering removes the finish (which is hard to solder to), and exposes the bare metal, which will hold solder better.

The above discussion does not consider crimp-on connectors, simply because they’re not something I, personally, would choose to utilize in a rugged environment – more so when considering the plethora of other reasons I’m not using them.  There are also some heavy duty crimpers meant to crimp the heavy duty solder-on connectors.  This is not something I would recommend, as those connectors were not designed to be crimped, and therefore are more prone to cracking and damage when installed in this manner.

All that said – the UHF connector, despite it’s wide use in radios operating up to 470 MHz, is NOT designed to operate that high!  On the plus side, the heavy center conductor can handle high power, but the connector wasn’t really designed to operate above 30 MHz.  From Amphenol’s website:

“Originally intended for use as a video connector in radar applications, UHF coaxial connectors are general purpose units developed for use in low frequency systems from 0.6 – 300 MHz. Invented for use in the radio industry in the 1930’s, UHF is an acronym for Ultra High Frequency because at the time 300 MHz was considered high frequency.”

So for HF applications, this connector is just fine, well, it’s OK.  The connector does suffer from some impedance mismatch issues – the connector varies about 50 ohms – it’s close, but not quite – especially at the higher end.  Additionally, loss increases – the connection alone adds a full dB of loss at 430 MHz, as shown in an experiment by VK3JEG, where the difference between UHF and N connectors were investigated.

One issue I’ve had, though, is connecting to this type of connector in limited access areas – and, when visual access to the connection is not possible, cross threading is possible (specifically in mobile applications).    For this reason, I chose to convert my mobile equipment (under 500W) to BNC connectors.

BNC connectors are good up to at least 2 GHz (often, they are advertised to be good up to 4 GHz) – far beyond the frequency capability of a majority of my radio equipment.  These bayonet connectors are easy to install with a small soldering iron and wrench, or crimped on.    Given the bayonet nature of these connectors, I’ve found them to be especially nice in those situations where I need to connect them in places where I cannot visually see the connection, and in situations where I need to quickly reconfigure antennas and transceiver connections.

Based on the discussions above, I’ve converted all of my equipment under 500W to BNC connections.  Unfortunately, this has resulted in an adapter at each radio.  This is a small price to pay to standardize on something convenient.  I have gone as far as putting these adapters on my HF radio outputs, CB outputs, and UHF/VHF radio outputs.  Since 50 Ohm BNC coaxial cables are fairly easy to find, interconnection to disconnect panels, VSWR meters, etc., is easy.

Above 500W, and in several other specific cases, I’ve changed over to N connectors.  This includes changing the actual connectors installed in my Palstar AT2K tuner, my Heathkit SB220, and even my MFJ-259B Analyzer (which needed to be changed, anyway, due to corrosion from the batteries).    Another catalyst for this change is my acquisition of a large quantity of N Connector coaxial cable at hamfests (presumably from some satellite enthusiasts) and other sales.  In addition, I picked up a number of N connectors at a pretty good price, still sealed in bags, waiting to be installed on cables.   The nice part about N connectors is that they’re good up to 11 GHz for the non-precision variety…  which is over ten times the highest frequency I have equipment for.  Additionally, they’re rated for 600W average, and 10 kW peak, again, based on Amphenol’s website.  This is far beyond what I normally use – even short duration CW tuning, an N connector will work just fine for “high” power operation (from the SB220).

 

Now, I haven’t touched on many other connectors, like TNC, F, SMA, etc.

I have a few TNC cables for various purposes, but only 1 or two pieces of equipment (such as the EMC-25 receiver) that have TNC connectors on them.  The primary benefit to the TNC connector is that it has a higher upper frequency limit (11 GHz), and is better in high vibration environments, since it’s essentially a threaded BNC connector (THREADED NC vs. BAYONET NC).

I have a number of SMA cables, as some pieces of test equipment (such as the SDR-KITS.com VNA), and portable radios have them installed natively – not to mention the fact that I installed them as connections for the IF taps on my FT1000.

F connectors, for what they are, are actually mildly interesting as an RF connector – they work fairly well beyond 1 GHz, and I’ve even seen them used on some GPS receivers.  I only have a few uses for them beyond television signals – such as dedicated receive antennas, where I can employ inexpensive TV grade splitters and amplifiers.

Finally, the Mini UHF connector…   not something I use much of – but every modern motorola radio I own (XTL series, CDM series, and MCS series) use Mini UHF connectors.  Older equipment and base/repeater equipment seems to typically have UHF or N connectors.    Overall, they’re good to 2 GHz, and fairly rugged, not to mention good for about the same amount of power as a BNC connector… they’re just not common on non-LMR stuff, so I can’t find much in the way of switches, attenuators, directional couplers, etc., with them on it – so the best way to handle them is to build cables with a mini UHF on one side, and an N, BNC, etc., on the other end.

 

Featured Image Originally found at http://leapsecond.com/pages/chess/

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