Hope you're all keeping well and enjoying your radio.
Can't help myself, enjoy this radio malarkey so much that I keep building things. (Makes for brilliant learning experiences if nothing else!
The latest 'homebrew' creation is after an opportunity presented itself in the shape of some discarded TV antennas.
Actually, they were 'discarded' in my own attic! Left over from when we had to upgrade our antennas for the TV analogue service switch off to go digital. They call it progress.....now I have more channels than I can shake the proverbial stick at with far less things worth watching!?! (Repeats of repeats and each channel labelling them as 'New' but only new to their network or channel not to the unfortunate viewer!)
Wouldn't mind but the new antennas are monsters yet don't seem to reliably pick up signals from a huge TV transmission tower I can actually see on the horizon from the upstairs bedrooms!
Anyway, whilst stripping apart the old antennas I began a bit of reading on Yagi-Uda beam antennas.
"Uda What?".....Mr Yagi was the front man and most forget about poor old Mr. Uda.
So after a bit of reading, researching, more reading, (some people really like their maths and numbers
), I came across the following site :-
ON6MU - Home Made UHF Yagi Antennas
Ah, here we go, some actual sort of plans without all the 'fap-fap' numbers, charts, diagrams thing going on.
The basic measurements helped, except the boom I had was a different size.....and the directors/reflectors were flat, not tubes....and a different size.....and in fact nothing I had matched the materials list whatsoever!
Hmmmm.....let's go for it anyway!
I broke the aluminium pipe that was the old TV folded dipole trying to straighten it, (Doh!), but luckily I had some 8mm soft copper pipe left over from my 2m Halo Antenna
project a while back. That'll make a new dipole and should fit one of the TV antenna mounts, (a bit of drilling to enlarge the holes from 6mm to 8mm helped).
When you make this dipole cut it longer than specified on the ON6MU site.....go on, ask me how I know that.
(Yeah, cut it flipping twice!) I made the reflectors & directors pretty much the same size as specified luckily just needing to trim the old TV aluminium struts down to size.
I didn't have another spare piece of aluminium to make the 'bazooka choke' mentioned on the site but a ferrite tube cut from an old PC VGA monitor lead should slip over the coax and do a similar job.
Then I marked the boom with a pencil with where everything should be placed but did NOT screw everything down yet......
I carefully balanced the dipole, reflector and directors on the TV boom, (15mm x 15mm), where the measurements/markings were made. Then tentatively hooked it up to my Zetagi SWR meter.....yep, CB SWR meter and as long as you have low power going into it, (My Baofeng was set to 'L'), it's quite useable at these frequencies. I then slowly moved everything back and forth until I got the lowest SWR reading, (1.8 ), and then finally trimmed down the dipole until the SWR improved even more, (1.2).
I still did NOT screw everything down yet.
With the aid of a field strength meter, (I didn't have one but a couple of pin diodes and an old analogue meter later I built one!), I then slowly moved everything back and forth again until I gained the highest readings on the field strength meter. It was at that point that I drilled the boom for all the fittings and finally screwed everything down.
So with a big 'Ta-Dah!' we landed up with this -
None too shabby eh?
It would have all been a little easier had my antenna analyser gone to 70cms, (MFJ-259B), or if I indeed had a NanoVNA....but I don't, so I managed with what I've got.
So how does it perform? (The real crux of the quest.)
Well, with my little Baofeng and the nearest repeater being some 15-16 miles away, (GB3OV), my 70cm activity has been a little lacklustre.
(I can only hit GB3OV if I hang out of the bedroom window!)
......Now I can hit SEVEN repeaters!!!!
All a clear radio 5 just by pointing this monstrosity towards the target repeater whilst sat in my chair, in my radio room. (Yep, haven't even mounted it yet!)
Think that'll do nicely.
I can even chat to my old Ham friend who is only 20 miles from here but is separated from me by a rather large hill(!). He opens GB3TU, (Tring), and I point my beam South accessing it thereby circumventing said hill.
Gain? - Hopefully whatever the ON6MU site says or as near as dammit.
Charts? - Yeah, not my thing
Anyway, thanks if you got through another instalment of my waffle. Been a while.
Don't be afraid to make an antenna out of what you've got laying around and if the maths and charts puts you off...simply ignore them.
Right, I have an old cordless drill lying around somewhere.....and a broken telescope equatorial mount....
Should make a nice antenna rotator!
All the best,