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Nano VNA H4

Even though I will not be on the air for another 6 months or so I have already been planning the first  antenna I will make.

The last time I actually made an antenna was over 35 years or so ago!

 

 

Delta Loop

After scouring websites, books and forums I decided on a vertically polarised multi band Delta Loop. I will have ample space for this antenna. Naturally, the length of the wire, height off the ground and so on will affect its performance, especially it's swr and its resonant frequency.  In the old days we used an swr bridge and our transmitter to determine what adjustments were to be made to an antenna to ensure resonance at the desired frequency, but it was a laborious job. 

So I looked into buying a new fangled Antenna Analyser. After much deliberation, especially about the price for an item I would use seldomly, I settled on a Nano VNA H4 analyser and ordered one.

Having never used any form of analyser to set the resonant frequency of an antenna, I ordered some bits to make a 10m dipole to use the Nano VNA on and familiarise myself with its workings.

I got the wire from a DIY store and RG58 coax with already attached PL259's, from a store online. I also ordered 2 glass insulators or 'Glass Doobies' as they used to be called. OrGlass Doobie Insulators thought I did. I ended up with 10 as they were in packs of 5 which I didn't realise.

I made the 10m dipole in about 15 minutes and put it up in the air about 12 feet off the gound. After setting the frequency range of the analyser, calibrating it, switching 2 of the traces off the display, and setting it to read swr, I connected it to the dipoles coax feeder. I immediately saw that the dipole was resonant at about 26.5 MHz. I trimmed a bit of wire off each leg of the dipole an that did the trick. 1.2 : 1 swr at 28.050 MHz. 

Nano VNA

I was amazed how easy the analyser was to use. But I am not going to explain how to use a Nano VNA here. There are ample tutorials available. My thanks to TheSmokinApe  whose video on You Tube was all I needed to get started with my Nano VNA..

Test over, the dipole came down and I put the analyser back in its box until next year, when the Delta Loop is actualy made.

I also played around with ChatGPT 4 to work out the lengths of the sides of the Delta Loop. The apex of the triangle will be at the top with the feed point at a corner at the bottom, making it vertically polarised. I could have worked out the measurements in the normal way with a calculator but I like AI. 

The length of the sides of the triangles were worked out by the AI using my specifications for the height of the mast / centre support and the height I wanted the bottom horizontal side above the ground. I specified that the total length of wire used at 43.5 metres.

The below sketch is a representation of what measurements the AI worked out. The AI took all of of 5 seconds. I will use these measurements as a starting point and see what happens. The height of the mast was only a guide, it might be a few metres higher, but the side dimensions of the delta loop will stay the same just with the bottom side higher off the ground.

I have downloaded free antenna modelling software (EZNEC) but have no idea how to use it - yet. When I have got to grips with it maybe the measurements produced by AI may have to change.

Delta Loop Measurements Suggested by Chat GPT 4

 

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