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I understand that the:

  • PL-259/SO-239 connector (so-called "UHF connector") isn't great for UHF frequencies, but is very common
  • N type connector is water-proof; and the
  • BNC connector is quick to connect and disconnect

From James Eagleson's YouTube video I can see that the PL-259/SO-239 (so-called UHF-connector) performs the worst over VHF, BNC is significantly better, with the N-type performance being comparable to the BNC.

However I, as a ham-in-training building his own SWL rig, haven't been able to figure out when to use which as my primary coupling for antennas and switches as the cabling comes down to my rig.

I, personally, plan on creating antennas for a wide array of bands. My first antenna is for the 2m band, and I plan on creating some UHF antennas, but most of them will be for HF frequencies.

When do I use which is best connector to use when?

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  • $\begingroup$ There are also F connectors. That's all I've used outdoors for years. Inexpensive, low-loss, easy to install, and handle the legal limit when used with RG-6. $\endgroup$ – Mike Waters Mar 18 at 19:44
  • $\begingroup$ @MikeWaters Really! Isn't the characteristic impedance 75 Ω? How do you handle that problem? $\endgroup$ – rclocher3 Mar 19 at 0:04
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    $\begingroup$ @rclocher3 Never been a problem here. A dipole is 75 ohms at the feedpoint, not 50 ohms. For my inverted-L, I use a tuner at the feedpoint. For a Yagi, it's a one-time adjustment. But even if it's looking into a 50 ohm load, it's only a 1.5:1 SWR. :-) $\endgroup$ – Mike Waters Mar 19 at 0:57
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For shortwave listening, it doesn't really matter – all these connectors are suitable for 30 MHz, and for reception you don't need to work with significant power.

PL-259

2m-band

If you, however, plan to work in the 2m band (2m being the wavelength, so frequency is, $f=\frac c\lambda=\frac{3\cdot10^8\,\frac{\text m}{\text s}}{2\,\text{m}}=150\,\text{MHz}$), then PL-259 definitely reaches its limits. That connector was designed before going "so high" in frequency was expected to be common for civil/low-cost radio equipment, and thus, the shape creates impedance changes over frequency. And that gets worse with increasing frequency.

UHF

Just to cite Amphenol RF, which probably are the most important industrial player in RF connectors: They do offer PL-259 connectors, but even they say "Impedance: Non-Constant" on their product specifications, for example: https://www.amphenolrf.com/083-1sp-15rfx.html

That's not really an option, to be honest, when handling power. Your amplifier will not like seeing its power getting reflected back at him. You will not like getting less power at your antenna than your amplifier generates.

Oh, and even they only say the connector works up to 0.3 GHz. UHF actually is defined to be 0.3 to 3 GHz, so nope:

It's called UHF-connector, but it's not good for what we call UHF, at all.

BNC

The go-to connector for anything that is high-frequency, but not outright microwave, at least in labs. It can be manufactured to a high degree of precision, which allows frequencies above 1 GHz to be transported well. If you spend more money, you can even get connectors that work up to ~ 4.5 GHz. These expensive connectors don't make sense unless both sides of a connection have the same precision. And you don't want to go up that far in frequency, anyway, probably

BNC is pretty nice for the lower UHF band, i.e. below ca 1.8 GHz. It's cheap, easy to buy from multiple reliable manufacturers (I wouldn't go for "sale boxes" on connectors – if you save 1€ on a connector to 50€ on cabling, but end up with something flaky, or lossy, you'll be sad). Also, they are typically able to withstand 1 kV of voltage – enough for high-power transmitters.

Cables that work with these connectors are cheap, and there's adaptors available to basically anything you want, from SMA over N-Type to Gardena garden hose.

You have to pay a bit of attention: BNC systems and connectors exist in 75Ω and in 50Ω variants – you need to pick what is identical to your system! (50Ω is kind of standard in RF measurement and lower- to medium-power systems, but 75Ω has typically lower losses and thus is preferrable if you have long cables delivering much power – but the 75Ω cables and connectors typically don't work for frequencies as high as their optically nearly identical 50Ω counterparts, soooo... it depends on what you have, anyway, but don't buy BNC stuff that doesn't say whether it's 75 or 50 Ω.)

BNC is also pretty nice as it's quick to connect and disconnect. It's, on the other hand, not as sturdy, and not outdoor-compatible.

N-Type

Kind of what you see the most in medium-power professional RF equipment's antenna connectors. Works up easily to 10 GHz (again, depends on the price, in the end), handles significant power, is sturdy, has low loss and excellent impedance match.

It's a bit more expensive than BNC stuff.

More of a hassle to connect, and disconnect, but very reliable once tightened (don't over-tighten!), and can be wrapped in self-vulcanizing tape to make a connection weatherproof.

N-type is used in most sensitive RF measurement equipment when BNC doesn't go high enough in frequency – exactly because you can tighten it precisely enough to give a very reliable low-attenuation connection, which isn't easily degraded.

Conclusion

You're not starting with a 1 kW transmitter. You'll probably be happiest with using no connectors outside, and BNC inside.

When aiming for higher frequencies as interconnects between low-power devices, SMA might be a better, because smaller, alternative to N-type. For high power, N-Type is pretty much your go-to choice.

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  • $\begingroup$ Thanks, as a follow-up. Is the SMA good for anything other than simply using as the terminal connector for my SDR? $\endgroup$ – Amin Shah Gilani Mar 16 at 11:49
  • $\begingroup$ yes? I mean, it's an RF connector with specified properties. It connects RF devices to RF cables, antennas and so on. At work, it's by far our main connector – between SDRs, antennas, on cables, for low-noise amplifiers, filters, splitters, clock sources… We never work with any significant power, so there's no need to look for anything larger. $\endgroup$ – Marcus Müller Mar 16 at 11:51
  • $\begingroup$ Would it be too much of a problem to add an SMA to your answer? I was given bad information that that connector wasn't a good connector for over 20 watts and therefore I didn't think to ask. I could also update my question to if you add this information and your answer would serve as a comprehensive reference for my friends in the future. Only if you're comfortable. $\endgroup$ – Amin Shah Gilani Mar 16 at 15:09
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    $\begingroup$ N connectors are usually weatherproof even without the tape, though the tape is still a good idea in a permanent installation. $\endgroup$ – Phil Frost - W8II Mar 16 at 16:05
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    $\begingroup$ @tomnexus hahaha! OK, that is kind of like a running engineering joke, the "XYZ-to-Gardena plug", just like the "Siemens Lufthaken" (Siemens aerial hook) for mounting things steadily in thin air, $\endgroup$ – Marcus Müller Mar 17 at 9:35

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