radionortheast wrote: ↑Wed Jul 02, 2025 8:44 am

Mongo82 wrote: ↑Mon Jun 30, 2025 10:44 am It was mentioned a mast being used as reflector, the way described does that mean the dipole would look like an H ((((

Suppose it has bit longer the reflector, I had one used to put behide a dipole in the loft it did work to a degree, it was mostly still omidirectional. The mast will be a longer than a reflector to get it off the ground, so I can’t see how it would do alot.

Northeast - the reasons that it didn't work for you are:

1. It was in a loft. You're going to get reflections off everything around your aerial, your radio energy isn't getting radiated (you'll lose most of it into the roof), and if the roof is wet with rain, you'll get almost nothing radiated!

2. You didn't have the dimensions correct. The distance between the radiating element and the reflector is crucial. If you get it wrong, your SWR will be abysmal, sending power back down the feeder. The impedances (real and virtual) of the aerial will also change - possibly quite radically - and it just won't work!

NEVER put a transmitting aerial inside a loft - you'll waste at least 90% of your expensively generated RF energy!

Mongo82 - You're right. A two-element Yagi (a radiator and a reflector) does look like an "H".

In answer to your question about the PL259: A friend of mine used to call them "audio plugs" because they're so bad at VHF frequencies! If you use a TDR (or a VNA) to look at the feeder from the output of the final PA filter, all the way to the aerial, you'll see that the SO239 / PL259 combination gives a big disconinuity in the trace. This shows that the socket and plug combination doesn't work very well, and causes reflections of its own.

Better connectors include the BNC (be careful to use the right impedance version - they come fractionally differenly sized for 50Ω and 75Ω) and the "N"-type. There are several other (SMA, SMB spring to mind) that also work well.

You may be surprised to learn that (at low power) even the humble RCA / Phono plug and socket outperform the PL259!

Unfortunately, fitting SMA plugs need the right tools, so most people use ready-made cables. They have the advantage that they provide a good match, can handle a few Watts, and give a physically robust connection.

The BNC is the one I'd usually favour for up to (perhaps) 20 Watts. You don't need any special tools, and the provide a reliable, low-loss connection. They're also easy to connect and disconnect, and you can get ones with the right collar internal size for your RG58 (or RG59 if you're going for a 75Ω system). I can't vouch for other suppliers, but RS Components used to supply a little pamphlette with their BNC connectors, showing how to fit them correctly!

For SMA powerhandling, it does 1.5kW on HF all day long, but 300W on VHF and it melts.