UHF Beam - That anyone could build!

Hi All,

Hope you're keeping well and enjoying your radio.  


As some of you are aware I've been having right old fun building antennas!

There's a lot to choose from design wise, some will never live up to their expectations, some are difficult to construct, some are downright weird at first......but some are rather easier.

The following is one that was much easier than anticipated, works as well as my Yagi-Uda 6 element beam in that I can also open seven repeaters with it from my location and I went all 'Blue Peter' on this one grabbing whatever was to hand.

You could all probably do something similar.

Here it is in it's 'sticky-backed' glory...



"WTF is that?" I hear you say.

Well it's two bits of copper welding rod, a stout cardboard tube from an empty cling film pack, (thanks goes to my Missus who asked if it was any use before she chucked it - she knows me well!), a piece of hardboard, but a good bit of cardboard would do in a pinch and some aluminium foil tape.

Couple of hours later, judicious use of a hot glue gun to hold it together and Bob's your Uncle.

Yeah, I didn't think it'd be up to much and was pleasantly surprised when I opened up the GB3TU repeater first go whilst hand holding this 'Arts & Crafts' antenna.
(In the house no less, in my radio room/spare bedroom, on a Baofeng! Tested all the way down to 'low' power which through a 50 dummy load measures as 0.9 Watts!)

The damn thing WORKS! Not only that but really well.....so much so I have plans to build a more permanent version of it too.


Now, you know you want to build one don't you?

No?

Well with a few adjustments on the measurements this thing would be perfect for those that like to use the slightly 'higher' frequencies above the Amateur 70cms.
(Shhh, I didn't say that. )

So I'll give you some details.....


This was all thanks to stumbling across an antenna image that lead me to the website of Andy Dunham G6OHM :-

https://g6ohm.webs.com/antennadesigns.htm

Scroll down the page a bit and you'll come across the details of how he constructed his own, (labelled "70cm Double Quad Beam"). The glorious example by his friend Roy M6CKI with what looks like a 'baking foil' reflector struck the deal for me to have a go at building one.

I actually used the measurements Andy suggested but did come across an online calculator if anyone is interested :-

https://buildyourownantenna.blogspot.com/2014/07/double-biquad-antenna-calculator.html

There are some other calculators out there but not many actually come anywhere near those derived from the formula(?)


Oh God, I've mentioned 'formula', 'calculations', etc. but exclaimed this thing is easy to build?!?!

Well put it this way, the damn thing spans some 40Mhz at less than 2:1 SWR and at first I thought I'd done something wrong with the NanoVNA! (Thanks again to the Charlie Tango member that donated it. ) Honestly, you could be way out with the cutting and bending of the antenna element wire and still have a working example.


You don't need a NanoVNA, you'd probably get away without measuring the SWR and best of all you could construct it with whatever you have laying around. (You'll notice my 'reflector' isn't square as the hardboard wasn't that wide - yet still works!)

It's frequency response is so wide you could hold it Horizontally, (for Vertical polarisation - weirdly at first), for FM repeater/simplex work and Vertically, (Horizontal polarisation), for SSB work. Same gain as the Yagi but take a closer look at commercial Yagis and you'll find you have to pick your frequency of use they being so narrow-banded.


So go on, build yourself an antenna.  


Just don't try this for HF frequencies, a CB/10m unit would be 10.81 metres, (35 and a half foot), wide!!!!


Once again more of my waffling. If you got something from it then it was all worth it.



All the best,
Victor

For those of a technical bent here is an article written by the venerable L.B.Cebik including some computer modelling :-

http://on5au.be/content/a10/vhf/ddq.html

Very well done Victor. Your first post gave my brain a lot to think about last night, a lot of mental calculations went on up there whilst I was led trying to sleep. I reckon that if I take down the trampoline and washing line, move the shed and rabbit hutch, I could just squeeze in a 10/11m version into the back garden. I wouldn't be able to hide it from the neighbours unfortunately and it would be directed straight at Italy so it won't be happening. Maybe one for Andy to consider to put up on his tower?

You might of said before, but how high are you Victor? Is it open from looking out of our radio room or do you have buildings blocking you to a degree? It looks like a small but effective design that would work really well for someone who is in a top floor flat or tower block. I am wondering how well I would get out on that band from a upstairs room from of an average sized starter home in the middle of a housing estate? I guess there's only one real way for me to find out.

Will have a look at cheap baufengs again later today. I'll probably get in trouble looking for a new radio again, but if I show her a design for an 11m bi-quad for the garden first I'll think she probably let me have a little £30 HT.

Victor, just one word

LOVELY !

well done, I miss doing home-brew I have managed to get a 4m dipole together along with a 3 element beam for 2m, ready for my respite excursion into north Wales, but nothing as glamorous as that beam.

Well Done again, 73 Tony

Hi Neal.

Much appreciated mate, was a bit of fun and had to share it.

Ooh, I don't think I'd ever contemplate a HF version and our Andy does miles better with his Quad beams. However I have been contemplating a 2m VHF version which I could place back to back with a 70cm antenna. Still big but I wouldn't get into trouble with the missus for it.

I'm not actually that high up Neal, 85 foot or so above sea level which is a bit of a radio hole leaving me with a mostly eastward path. Flipping East Anglia for you(!)

I know my HF set is still out of action but trying to contact my old Ham friend when it was working was difficult with every band and mode even attempting NVIS to 'hop' over that hill that blocks my westward path. Surprisingly with the Yagi and this beam I can fire from Bedfordshire down to Hertfordshire to the Tring repeater which then gets to him in Buckinghampshire. Long about the houses trip but works!

I had a huge smile on my face as we tested these antennas hearing him going from a '/mobile' call sign to him happily announcing "No longer mobile!" parked on his drive. We were chuffed to bits and can now chat QTH to QTH.  

The best bit is that this antenna was so easy to build compared to the Yagi with much more easily sourced/scrounged parts. Amazingly I was simply hand holding this antenna on my lap sat on my chair in the radio room. So not really much of a clear path to start with!

I've since tried it downstairs and only lose two of the furthest away repeaters indoors but gain them back again outdoors on the appropriate side of the house. I think it's an antenna that would suit all sorts of occasions.



Yeah, get yourself an old coat hanger and nick some of the Bacofoil from the missus and knock one up. (Or go the whole hog with metal mesh etc.) Strap the whole thing to a Baofeng and see how you go mate. It can be fun up there on UHF as our PMR guys will tell you with surprising transmissions distances especially with the Amateur repeaters.
Plus it's budget friendly......so much so even my Missus is happy.  


If you build one you'll have to let us all know how you get on.


All the best,
Victor

Hi Tony,

I agree, it is rather lovely and I'm not bigging myself up either it's a wonderful antenna concept!
(Thanks again to G6OHM for his share on his website)

I love nothing more than a bit of Home-brew from simple wire antennas to full blown projects. Had to share this one as it was so easy to build with instant results. That's why I showed the 'concept' version in all its glorious 'Blue Peter' state!


Sourcing parts for a more permanent version now and hoping to construct a 2m version. I may well get you one day with a suitable bit of tropo on one of your excursions mate.  


All the best,
Victor