Okay, so re-thinking the problem… one issue I have is securely mounting the whole lot to the PL-259 connector at the bottom. That’s always going to be the weak point, as I don’t have the luxury of making the connector integral to the antenna.
So I’ve re-thought my plans a little bit. The original rod was nice and light, and more than long enough to make a vertical sleeve dipole, which is what I originally had planned before I dove off into more complicated designs like the dual-band flower pot. Perhaps the way forward is to turn a base out of a 30mm block of wood and make it a fixed base antenna.
Going back to the original fibreglass rod, I noticed that the heat-shrink hid a small length of hose, and that could be stripped away to give me just the bare rod. This, could be jammed into a clamp-style PL-259 I had laying around, meant for RG6 coax. There’s enough room for a length of RG58 to come out of that connector alongside the fibreglass rod. I could then make a sleeve dipole by peeling the outer sheath and sliding the shield back over the coax.
This is the length of coax being prepared. I normally ignore velocity factor, but in this case I decided to factor it in, I can always strip the coax back further to make it longer.
I normally tune my 2m antennas for 145.7MHz which is mid-way between 144.1MHz and 147.3MHz. I don’t do CW so the bottom 100kHz of 2m is of no interest, and there might be some simplex stuff between 147.3 and 147.5MHz, much of that upper 500kHz is repeater output frequencies, so I’ll be listening rather than transmitting.
With that in mind, 145.7MHz gives a wavelength of 2.059m… quarter wavelength is 514.75mm. Accounting for 0.66 velocity factor for RG58/U coax, I get 339.7mm, call that 340mm. That’s the length of exposed braid seen in the above photo.
I found that this particular coax is pretty stingy on the braid, so when I peeled it back along with the foil, I found it difficult to get that to wrap around properly. Plus I had managed to accidentally cut the shield. Ahh well.
I have some adhesive aluminium tape, so I used a length of that to replace what was lost. Bonus being it adheres the coax to the fibreglass rod. Downside is it won’t take regular solder. @pelrun pointed out (on Slack) I need special flux for that, which I do not have. (Did try some flux I happened to have, but it was no use.) So workaround, use some scrap stranded wire, solder the braid to that and wind it tightly around the top of the aluminium tape and solder it.
At least at DC it checks out. I’ll try it out on the radio in a moment.
That’s the full antenna completed there. I just wrapped some tape around the bottom to secure the rod in the connector, long-term I might look at what I can make to clamp around that and better secure it, but at least it’s together now.