Yaesu VX-5R Antenna Stub

[metrologist]

I bought this tri-bander used and it did not come with the 6m antenna stub, so I was thinking of making one.

I started with 56" of insulated wire connected to the threads at the tip of the base antenna (where the 6m or 2m/70cm stubs connect) and measured VSWR valley was a little below the target frequency. I wrapped that wire around a wood dowel and the VSWR valley was up around 100M.

Not sure which direction to go now. Any ideas what magic they have in that stub?

BTW, with the 2m/70cm stub, the VSWR measures 1.2:1 and 2.7:1, respectively. This is on an antenna analyzer with N-SMA adapter. I measured the Diamond SRH320A antenna and saw 4.4:1 and 1.1:1, respectively.

[Geoff-AU]

1/4 wave of straight wire and 1/4 wave of coiled wire behave VERY differently.  coiling the wire creates a loading effect, which lowers the resonance frequency.  100MHz will be one of the harmonics.  extreme loading has probably given it such a narrow (high Q) fundamental resonance that you missed it.

also don't forget that for a handheld, your hand grabbing it creates the other half of the antenna.  so classical rules like "1/4 wavelength" might only get you into the ballpark.. it'll need plenty of adjustment.  or you can add a tiger tail (?) which is a tuned counterpoise.

[metrologist]

It could have been a mode. My antenna analyzer can sweep from 2MHz up, but I might have set it to sweep from 25MHz to 500MHz, and could have missed the primary. I'll do it again, if we have power tonight...

[metrologist]

Well, I tried all sorts of wrapping various wire lengths around a dowel as an extended antenna stub with various loading positions (continuous, top, center, bottom...). While I can get a return loss or VSWR dip in center band, it's too narrow and not quite low enough. The Smith chart will show almost zero reactance but with very high resistive impedance, so it wouldn't radiate much.

Since it's an extra piece, might as well just build or buy a complete antenna for the 6m band.

Here's an option: Diamond SRH-940 covers the three bands my HT covers.

Or I could just go with, nothing's ever happening on 6m anyway.