While experimenting with LoRa, I needed a better antenna at home for range testing the LoRa tracker. I came across this Jpole antenna calculator and used it as a starting point for dimensions.
As we are presently locked down and and travel is only allowed for essential reasons, I had to use materials that were on hand. I found some 6mm copper pipe, and although its a bit soft, it would be easy to solder to and should stand up ok outside.
In the past, it’s been weatherproofing the Jpole match that has been the challenge. I found a weatherproof looking plastic enclosure in the junk box that looked like it would protect it.
A test was done with the coax feed solder tacked onto the pipe at the calculated point using the calculated lengths for the radiator and stub. A VNA was connected and the match was perfect without any need to make an adjustment. The return loss read off at just over 30dB with the antenna in the clear, away from any metal.
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Return Loss
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Jpole Match
Stabilising the radiator and stub inside the box are some 6mm cable clips. The nail was removed and the hole left was a perfect self tap diameter for 2mm stainless screws. The coax is decoupled with a ferrite about 25mm long. Not sure of it’s properties as it came from the junk box. It seems to do the job as the return loss is not affected by touching the coax.
Copious amounts of neutral cure silcone sealant were added around the radiator and stub entry to the box. A drain hole is left at the bottom of the box incase water does get in.
After fitting into the box and adding the sealant, the match did not change too much which was surprising. It’s now on a pole outside at about roof high, ready for some LoRa testing
