abcd567 "The one thing I have tried & know is that the 70 mm dia Can gives better result than 55 mm dia Can which gives better results than 25 mm dia Can. "
I found the same, Larger cans performed better but I dont know what the upper limit is ie the sweetspot
Thanks all, so I’ve tried to cut down the coax cable <5cm still bad, I’m starting to think that it could be the connector (pig tale?). Anyways thought I’d give it another go at DIY, based upon the original post on this tread would these be appropriate:
Have you tried just optimizing the whip as in the picture from abcd with the can below the antenna?
That way you don’t need to buy an adapter.
Do NOT cut the whip. Unscrew it, and use a thin wire as whip
If the wire is thin, it will be easy to wrap it over the threaded brass stud of the magnetic base. With thick wire it is a bit difficult.
Placing whip antenna over a metallic can or metallic plate is the easiest thing to do, and gives the biggest improvement to the performance.
Added advantage (if plate or can is made of iron/steel) is that it keeps antenna vertical and prevents antenna from falling
Thanks both,
I thought perhaps it might still be worth trying a spider one as I could mount it in a more favourable position, is the DIYed original antenna roughly equivelent to the DIY spider?
If all else fails “fixing” the original by curling wire around can certainly be done (I’d rather not chop the antenna), and atm it is on top of metal surface which has indeed seemed to have helped, despite it not being the optimal length.
I’m assuming them parts look good then? I have both the time and the inclination to mess about with spider just as it’s fun to try make your own!
At the beginning of my feeding experience i’ve also built a very simple spider as shown above. IT was a lot better than the small whip antenna.
Give it a try, doesn’t cost that much
Yeah you’ll need a suitable adapter that actually works.
Then you can do DIY as much as you like 
Just with that adapter you had it didn’t seem to make much sense.
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Derivative of the spider …
If you have some cheap coax, the insulated center wire can be pulled out easily from the rest of the cable. The size of the soldered loop allows it to fit over a coax connector.
It’s easy to try different length center pieces as the center piece isn’t soldered - the stripped end is just pushed into the coax connector. Having an impedance analyzer makes it easy to fine-tune the length of the center radial and the angle of the ground radials.
I later switched to the SMA-to-F coax connector cables and put the antenna in a weatherproof box with Raspi+tuner so the cable length would be short. I used the Raspi’s WiFi for the internet connection so the box only needed the 12V power connection (used a 12V to 5V step-down converter).
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Why measure to the your red line and not a blue line?
(I asked the same question last time you posted this pic, but never got a reply)
You are right. The correct measurement should be from blue line. However, the sketch is not to scale. The blue and red lines in reality are almost coincident.
When I have to cut the whip, I actually measure without opening the base plate. I measure from outside, between center of coax at it’s entry point, and start of stud, as shown in green in sketch below.
As the whips from different manufactureres are slightly different, this distance varies by few mm from whip to whip.
Finally, a few mm error practically does not noticeably affect the performance of whip.
True - it’s never going to be a great antenna. As we’ve discussed previously, the coax supplied on these is (to put it politely), nothing special. An easy antenna to get started with, but hardly a performer.
But much better than keeping the original one.
I started with it and after a few days i replaced the whip with a piece of copper in the given length. I did not have perfect tools, so the length was not cut to the perfection.
However i had immediately a 40% better reception. It’s a good starting point for people doing the journey with DIY antennas.
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Does anyone know the impedance of the cantenna? Is it OK to use RG6 coax with it?
The characteristic impedance of a 1/4 wave antenna on an infinite ground plane (ie. the perfect build) is 36 Ohms
https://www.sciencedirect.com/topics/engineering/monopole-antenna
Now that I know it’s called a “monopole” I was able to find this information which shows how the impedance varies according to the angle of the droop of ground plane radials. On the cantenna it seems that the side of the can is the ground plane, so is at a 90 degree angle which offers around 60 ohms of impedance. So, while a 52 ohm low-loss coax would be better a 75 ohm one would be OK too. Good, because all I can get here is either RG58 or RG6 and I plan to use RG6.
RG58 has far too much loss at 1090MHz
If you use RG6, get a quality brand. If you use something from your local $1 ‘bling and trinkets’ shop, you’ll end up with some third rate garbage.
To be suitable, RG6 needs to be rated for cable TV or satellite use.
Measurement of Antenna Impedance is influenced by the length of coax (in terms of multiples of wavelengths) between antenna and Measuring Instrument.
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I got ten meters of Cignal satellite coax made by Perfect Flex in New York, with a male F connector on each end. It’s the best available in my area (Philippines.) For now I’m making do with 15 meters of RG58 borrowed from my HF antenna as I’m still waiting for more parts including F female to SMA male adapters or I’d already be using the RG6. I’m just using the short antenna that came with my NESDR SMArt bundle for now but I plan to replace it today with a piece of 52mm wire wrapped around the stub and also try to get the antenna outside of my upstairs window instead of inside the room near the window. That should give me a bit more north-south range as my concrete walls won’t attenuate signals in those directions anymore. The mag mount is on top of an overturned soup can and about four feet off of the floor.