The Problem With PL-259/SO-239 connectors

many 1090MHz antenna construction plans use the common “UHF” bulkhead connector as a “base”.

Originally the connector was designed to carry signals at frequencies up to 300 MHz, but later measurements reveal limitations above 100 MHz.

Notwithstanding the fact that we are using these connectors as receive signal path components, and that is certainly less critical than transmit paths, the fact remains, the UHF connector is not the greatest at 1090MHz. … sults.html

What about F- barrel connector / panel mount bulkhead connector? These are designed for Satellite TV signal 950 Mhz to 2050 Mhz.

I built my ground-plane antennas using bulkhead N-connectors because of this. They work pretty well, and are a bit more sturdy than F-connectors even if you need an adaptor to connect to them.

F Connectors would seem to be the most appropriate for this endeavor, considering with these connections and RG6 it is possible to make an uninterrupted 75 ohm run from receiver to antenna, even incorporating amplification with no changeovers as you have demonstrated. That said, a few tenths of a dB here and there aren’t going to destroy the overall system performance on receive, but changeovers do add up.

I have been using RG6-Q coax and F-type connectors exclusively with good results.


So it looks like my panel mount BNC and the pigtail are 50 Ohm. I take it that 50 Ohm to 75 Ohm is a bad thing to do? I looke on ebay for BNC to MCX but I’m not finding anything as far as resistance/impedance values. A quick google search shows that 75Ohm BNC’s have less (or no) dielectric? (I live about 10 minutes drive from Fry’s Electronics, and I’ll see what I can find there, although I’ll have to order online for pickup to keep me from buying a lot more than what I intended to purchase! That place is like Toys’R’Us for big kids!)

The quick answer is that you will see little to no difference using your 50ohm BNC to MCX panel connector vs a 75ohm BNC, or connecting a 75ohm BNC to a 50ohm BNC. They all will work fine for this receive application.

Let’s say you build an antenna on a F connector, like the Cantenna. On the radio end, you could get a** BNC 75ohm twist-on** type connector for RG6 PVC. No soldering needed, no crimping required. These are commonly used in CCTV applications and Fry’s would have bins full of them for $1.79. That would connect directly to your panel connector/MCX.

Thanks, I just picked up Gordo’s Technician Class book and was browsing thorough the impedance mismatch section and I remember there have been some discussions here about issues when going from 50 to 75 Ohms, and trying to keep the system all the same. I have a bunch of 50 Ohm connectors, but the coax is 75 ohm… I’m sure I’ll learn all about that later while tweaking the stations.

Do you know if the Ebay Spider is 50 or 75?

(And I have no proclivity against soldering, would give me an excuse to finally upgrade from the POC 30W firestick that I have now, lol…)

My original spiders were built with SO-239 bulkhead connectors. I’ve since built with N bulkhead connectors and noted a modest increase in performance when using them.

It’s 50 ohm.

No SO239, no N-connector, no F-connector, … Spider with no connector at all :smiley: