Which coax is it? (Asking for a friend)
Looks like LMR-400 if I blow up the photo, but the resolution isn’t very clear.
That’s not very helpful for your signal! When the strands of the braid don’t make good contact with each other, the loss goes way up.
If you find yourself stuck on a summit with such coax, vigorously shaking, wiggling, and twisting it along the whole length will sometimes help to rub off the corrosion between strands, temporarily reducing the loss. But the appropriate long-term solution is to toss it in the bin.
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Yes you right with the coax ! I got back into radio after a long break of approximately 15 years after buying a Baofeng UV5r to listen to the VHF marine band ,in that period I had moved house and disposed of all my radio equipment. For some reason the dodgy RG58 had avoided the downsizing. As an orignally a short term measure I used the Rg58 and never changed it till now.
LMR400
Sorry, I should have posted a drawing. I found a couple photos online for versions with a single 70cm element on one side of the 2m element. Sometimes it is hard to imagine that it can be that simple!
Do make sure that the feedline is perpendicular to the antenna for some distance. Easier to accomplish in a loft than on a mast on a summit.
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O.K I finally got round to making this , as you can see very Heath Robinson ! It a prototype for testing purposes !
I looked at it and thought your having a laugh ! I first tested SWR on 70cm and it was just over 3.1 , then tested Repeater access I could just about get into GB3HN at 10 miles almost line of sight ( 1 Watt) I then trimmed about a cm off as is was resonating at 420mhz ,1.4.1 SWR and all of a sudden I had access to GB3HN with a good returned signal. I then tested the other repeaters In and a full strength signal from GB3RR about 15 miles ( bad path) A good returned signal from GB3KR ( I can just about make it from the base antenna) and I’m not theoretically in it’s footprint , and again a good returned signal from GB3KA ( only 6.5 miles away but a really bad path) GB7CC at 40 miles ( bad path ) again usable with noise. I thought wow this is working well ! I then tried 2 meters thinking O.K 70cms works but I’m guessing it’s killed 2 meters. Full signal from from two localish repeaters ( 10 and 15 miles) a workable signal from GB3CG at 25 miles (ish) and a fully usable signal from another repeater down in Banbury ( 45-50 miles away). Back to the 2 meter 1/4 wave Only GB3HN at 10 miles was even activated, signal was poor at best ! I then swapped back and forth multiple times and the results were the same.
2 meters were unaffected on both antennas.
I am truly surprised that something so simple and easy to make works so well. Now I just need to order some more spring wire in order to build a more substantial one and also find a way of making some sort of former to keep the coil stable during mobile operation.
Here is a link to the original article
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Right as I have a weekend to myself I have been playing with antennas, I first built a 2/70cms ground plane using the same design as the mobile antenna above and connected to my new LMR400 cable. I’m not sure why but I decided to build each ground plane leg in the same way as the driven element. A quick SWR test on the edge of 2 and 70 cms and all was well without any adjustment and I decided to have a few tests on both bands first contact was with Peter G7RPG ( of HUBNET fame) at 118 miles with only one watt wow ! I must of built the ultimate antenna ( or maybe there was a lift on ! Further tests showed a major improvement of all repeaters although I couldn’t get everyone perfect from one position as to get one good it end up shielding another, using the best position for all there was still a great improvement.
Here is the beast ( as you can see no expense full stop)
As there was no way I could get GB3HN well and still get the others well I decided to use the original coax ( rubbish RG58) and build a beam. I found a piece of trellis fencing which was 60 cm after a few calculations from an online Yagi design site I came up with a 5 element design which gave me 7.8dbd ( I’m putting it at 6 dbd to allow for my errors in measurement minus 2.2 db loss of the rubbish coax now cut down in length to reduce loss and get rid of the blackened coax braid ( water ingress) After checks ( again SWR was perfect) Have a guess who my first contact was with through GB3HN and HUBnet ? Peter G7RPG the same person who I had made the 118 mile contact on 2 meters ! I then listened back to our contact using the HUBnet website and my 500mW was doing really well.
Here is the pic of my 5 ele beam ( again as you can see no expense again )
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I tried this one today ( I didn’t photograph it ) I made it out of soft copper wire in a similar manner to the mobile antenna above. The tests showed it was far better than a 2 meter 1/4 wave on 70cms but not quite as good the 2 meter 1/4 wave on 2 meters but not far off ( not surprising) Just after I finished testing Mr Amazon Driver arrived with the 1.5mm spring wire so I have built the first antenna with the single coil. To stop the coil deforming in mobile use I have temporarily used a cocktail stick taped to the two upright sections bridging the coil, Full mobile tests tomorrow. Any way here is today’s antenna design ( not mine just found on the net) Performance on 70cm is identical to the the 5/8th wave design of first antenna and I do think in use it would be easier to put the coil on a former to stop it deforming in mobile use but then it is more difficult to wind the coil using the spring wire as it is so stiff and the coil is so narrow.
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