Jpole for 70cm

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.

Return Loss

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

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7 Responses to Jpole for 70cm

  1. Andrew VK1AD says:

    Hi Glenn, how close was the M0UKD J-pole calculator measurements. Did you make any adjustments to the spacing between the active and stub elements?

    Regards
    Andrew VK1AD

    • vk3yy says:

      Hi Andrew,
      The MOUKD calculator was spot on in my case. It was calculated for 433MHz and as you can see from the sweep, it is almost perfect. I understand that the spacing between the stub and main element is not too critical, the spacing came down to a nice bend radius on the copper pipe in this case.
      Cheers, Glenn

  2. Paul Taylor says:

    That long narrow box is perfect for it, you must have a few nice goodies in your junk box. You can do Lora tests to and from supermarkets 😉

    • vk3yy says:

      Yes, the box was perfect, was looking at something from Jaycar originally. Either supermarkets or Bunnings or maybe a work run if there is one this week. The tracker reported over an 10km path using that Jpole as receive.

      • Paul Taylor says:

        10km, that’s impressive, presumably line of sight. You’d get reasonable coverage from a summit, over that range. Back to a car, maybe.

      • vk3yy says:

        Surprisingly it was not a line of sight path! It must have been a fluke. I will post the path profile in the LoRa Tracker post.

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