PL259 Versus BNC Plugs

 So it seems I may have found the problem I'm having with my VHF / UHF setup. I took some readings on HF frequencies and everything seems fine. After a little research, I discovered that a PL259 plug is apparently at it's limits at 100 MHz. A better choice for these bands would be the BNC or N type connectors. A quick reference to Wikipedia states:

Despite the name, the (PL259) UHF connector is rarely used in commercial applications for today's UHF frequencies, as the non-constant surge impedance creates measurable electrical signal reflections above 100 MHz.

Either this had slipped my mind or I never new about it! I have never liked the PL259 plug, but most radio equipment is manufactured to take these plugs. So it looks like I'll be doing some conversions. Caution is required because not all BNC plugs are the same. Some are only for CCTV applications and are probably not suitable. They need to be stated as 50 Ohms and for up to 3GHz usage. Also, if using the screw-in type, it is a good idea to check for continuity and short circuits on your coax afterwards. (I speak from experience here!) There are some handy converters on the market - see below.

PL259 to BNC converter.

BNC connection plug (50 Ohm Amphenol type or the screw fit).

Update:

 Well the connectors have been changed for the VHF / UHF side of things now and the analyser was connected up for testing again. To be honest, it hasn't made that much difference. I have only changed the connectors back to the antenna switch though. Maybe if all the connections were re-done it would improve things. Also, maybe some dedicated coax for VHF / UHF applications. That will be a work in progress. The system is useable as it is.

QFH Install

 So the rain stopped today and it was quite a nice day. The Quadri-Filar Helix Antenna has now been installed. I had to join the coax run indoors because it wasn't quite long enough to reach the antenna switch. I did this with two PL259 plugs and a back-to-back socket connector. (check for continuity and shorts) So now there is a mix of RG58 and RG8 Mini going to the antenna. Not ideal but it might suffice for what I'm doing just as long as the SWR is OK. Just hope there's not too much loss. A quick test with the analyser produced these results:

The image shows a sweep from 120 MHz to 150 MHz. All the markers are around an SWR of 2.

This image shows a sweep from 400 MHz to 500 MHz (100MHz sweep?) I'm not sure about this trace - it seems odd. All of the SWR readings are showing very low. Maybe I'm operating outside the parameters of the analyser (100MHz), It could also be that the antenna doesn't work on this band. It is, after all, designed for satellite reception on the 2m band. I'm not sure. I may have to delve a little deeper here to resolve it.

Testing the receive ability showed it to be working well on the 2m band. I tried the SWR meter on this band but it was reading quite high transmitting from my UV-5R handheld at 5 Watts. I don't know if the SWR meter is suitable for this frequency though. More checking required.

A New Start

 This will be my new home from previously posting on my M7GBO blog. As mentioned before, I am currently working on improving my VHF/UHF setup and I am in the process of moving my QFH antenna.

The problem I have at the moment is the weather - it's atrocious! Just waiting for a dry spell because we've seen nothing but rain for a good few days. When erected it will make the working of satellites much better and also my general 2m coverage. If you would like to see what I got up to before this blog, check out https://M7GBO-UK.blogspot.com