Meant to get back to this thread earlier, but lost track of it. Responses below are not an argument or an attempt to fuel one, just the way I see the hardware.
I am not an RF engineer, so I will not offer that kind of opinion.
I am an RF Engineer, with more than 35 years in the field. However, as most of my professional history is at frequencies significantly higher than HF I might have a bit of a bias against lower quality or marginal quality connectors.
The position I stated before is my opinion, and what I have found to be true, both in professional use and in hobby use.
But I have designed dozens of electronic devices in the field of audio, and I have also manufactured them for profit, and owned those businesses. So, I feel competent to offer an opinion about cost strategies in general. Yes, the RCA connector would cost some cents less than another connector. But no, that cost saving probably is not the reason it was used. You wouldn't use 150 high quality parts, and then toss in one cheap one to save a few cents as a cost strategy. That would make no sense to anyone in business. I suspect they could use any connector in that spot they wanted without undue concern over their profit margins. IMO, it was used because they considered it to be the one which would offer the most convenience to their users. I didn't know that, because I have never owned a SW receiver before.
I can only back that up with their message to me, which says in effect that for "receive only" radios, they considered the RCA to be the most common. Now, if that's incorrect - so be it. But I don't see it as useful cost reduction when there are dozens of other opportunities to lower the cost far more substantially without attracting the least bit of attention.
Unfortunately that statement (RCA is the most common used in receive only radios) does appear to be incorrect. RCA appears to be a very small minority in the currently , or recent past, available receive only radios.
For example, looking at the currently available line-up of radios on the Universal Radio Inc web page (by no means authoritative, but probably a good starting place as an example of market population today) of 11 radios listed in the Shortwave Tabletop category only the Ten Tec RX-320D uses an RCA for an HF antenna, everything else is either BNC or UHF (PL-259 / SO-239), except for the alternate high impedance input for the R-75, which is a spring clip input. A quick look through 20+ portables resulted in several odd antenna connectors, from BNC to clip terminals, but not one RCA that I saw.
RCA is simply not used very often today for HF radio applications, and has not been for decades. As far as I can tell it was never used by the majority of radios, although it used to be more common than today.
The only advantage RCA offers today, for this kind of application, is in cost. At its best, with regards to performance, it is "as good as" the next cheapest thing, and it is never better than something like a BNC, TNC, UHF, N-Type, SMA, etc. It can be argued that RCA is also more convenient, but that is personal preference. It can be easier to build cables for at home.
I should clarify for all. There are no RCA connectors on the DX Engineering ARAV. They use F connections on their matching unit (as does Pixel and likely Wellbrook).
No, the Wellbrook does not use F connectors. I know you said “likely” and were not making a hard statement, just adding to your knowledge base here. The Wellbrook (at least my 1530+) uses BNC and UHF connectors only.
Personally, I use RCA adapters on my Pixel and the ARAV in the house for quick disconnection during a storm. Never had an issue. I always make comparisons before I make a switch such as this. I'm sure there's some gadget somewhere that will reveal that I'm losing something in the process, but my ears sure can't tell. Adapter or no adapter - sounds the same to me. Weak signal reception doesn't change. The Excalibur reports the same signals across the board rather or not I use RCA adapters. Perhaps I'm missing something. I would be interested in hearing thoughts about RCA adapters, as the main focus seems to be a direct RCA on a receiver itself, rather than using them as adapters. Though I would have to imagine that if impedance matching is a concern when they are present as an antenna input on a radio, then using RCA adapters would be a concern as well
When RCA connectors are new and in good condition, and at HF frequencies, any difference in a receive only application will be negligible. Sure, it might be able to be measured, but in real life, for most people, it makes no difference.
The problem with RCA, as I have seen them in use, is as they age they tend to degrade performance faster than BNC or UHF would. This is particularly true if you are cycling them often, as in disconnecting the antennas when you are not home or when a storm approaches.
As I said earlier RCA is relying on friction fits for both mechanical and electrical connectivity. This friction fit often loosens with age. As the connection loosens there starts to be a performance hit. But because this happens slowly, over time, the user might not notice a change. It is often not until a problem becomes large and is noted, then the connector replaced, that the user has that “ah ha!” moment of realizing there had been something going on for a while.
It is primarily because of this more rapid degradation over time that I refuse to use them, even in a receive only HF application, unless there is no other possible answer. I have replaced OEM RCA’s on equipment with BNCs several times just to get around this issue.
I'll also mention that there was quite a discussion on another board concerning the use of RCA adapters. After reading those comments, I decided to use them as I prefer to pull rather than unscrew when weather gets ugly.
For quick release the RCA is certainly preferable to something like UHF, however they are really no faster than BNC to disconnect. With BNC you just twist and pull. Of course, with RCA you can just yank the wire, without touching the connector itself, but you really should not be doing that to any kind of plug/wire, let alone coax.