What started out as a sub 10° temperature day, soon warmed up. A very convenient reason Dave ZL1DL used to stop sweeping the driveway; he was dressed for the lower temperatures. Actually, it was the arrival of others that really led to more interesting activities.
Martyn ZL3CK headed off to a field for his first try at POTA. Using his 5W K2 and PAC12 vertical, he made a couple of contacts on 7090; ZL2AJ and ZL1TPZ with 5×0 reports! Harry ZL1BK, reeled out his QRP endfed for a bit of testing. The wire reel, a builders chalkline winder, houses the balun as well.
First up was checking the frequency response of the recently repaired 40m dipole. The balanced feedline had been shortened and this resulted in a significant retune of the coax to balanced line matching unit being required. This suggested the feedline was not just feedline but part of the antenna. The feedline was disconnected from the match unit and connected to a nano-vna. Those still awake might recognise that connecting a 50 ohm VNA bridge to a 600 ohm feedline is questionable at best. And yes, that’s right. Strange results were observed depending where on the feedline, the nano was connected. So a switchable impedance unun was introduced and really, we achieved such differing results ( big resonant frequency shifts! ) at different impedances, at the end we reconnected the feedline to the match unit and called it good! To achieve meaningful results, the transmission line needs to be terminated in 600 ohms resistive. We need to manufacture a 600 to 50 ohm balun just for the test. Pleasing though was the near -30dB return loss and confirmation of the wide bandwidth of the 3 wire dipole.
A lot of radios with orange coloured volume controls have been appearing in the hands of members, and one of the features of the Quansheng UV-K5 is an RSSI indication. Today this was used to demonstrate the relative signal absorption of VHF / UHF through foliage. We just happen to have some suitable bush nearby – how convenient!
The 5775 repeater antenna is wobbling around from vertical – most likely from a failure of the pinning bolts in the base casting, so repair is back on the todo list. Mark ZL1MRT wanted to clarify the length of the antenna support pole on the top of the building. A measuring tape was never going to hold a straight line when proffered (is that really a word?) vertically. However, with a bit of trickery (supporting 3m of the measuring tape inside a pipe held vertically), we managed to measure the lower pole at around 6.4m and estimated another 1.5m for the top section. The antenna mounting is therefore around 7.7m above the top roof level. Mmmm – short straw anyone?
While on the roof, we took the opportunity to reterminate a disconnected feed jumper on (or was that off?) the V beam. Harry ZL1BK and Dave ZL1DL patched the feed back together with a wire clamp – job done.
And surprise surprise, afternoon coffee to round out the day!