PMR-446 8-element Yagi

Post by **ntj** » 07 Jul 2007, 18:28

Hi folks,

Hehe, I know Fez has just made a similar thread but here are some notes from our homebrew sesh yesterday in case they're of use to anyone

We couldn't find a design that was perfect so set out to mix and match the best bits of others. We used this Yagi calculator to get our dimensions and went for an 8-element beam. If anyone wants the exact parameters used, let me know.

The true stroke of genius was using 6mm threaded rod for all elements. It's really really strong and because of the threads alignment is easy. The boom is 21x45mm timber. Total cost about ?4

Not wanting to fuss with tuners, we went with a J-pole as the driven element so we could use a gamma match device (inspired by the diagram near the bottom of this page). The threaded rod made this extremely easy!

I replaced the antenna on one of my Binatone MR 150s with a BNC socket. I also knocked up a little SWR meter, but now I don't think it's really suitable for UHF.

With the SWR meter not behaving right I got out my trusty homebrew passive field strength meter (yep, both those little meters are from the same stereo!):

The meter responded strongly to the antenna and demonstrated the directional nature of the beam very well. The readings we saw from the front and rear lobes were in the ratio expected from calculating the gain out the front and the gain out the back of the reflector, which was encouraging

Today I set up a jig to try and peak the antenna by pointing it straight at the meter. I managed to find the gamma match sweet spot so although I don't have a UHF SWR meter I'm confident it's working well.

It certainly pulls in a lot of random PMR when I sweep it across the town I overlook. Looking forward to some range tests!

Post by **g0slq** » 08 Jul 2007, 14:02

Again, I like this idea, the thought of getting as big a signal as far as possible from 500mW seems like great fun.

Post by **ntj** » 10 Jul 2007, 20:29

I've got a better UHF SWR meter design so I'll get that knocked up in the next couple of days. Hopefully Fez and I will be able to do some range tests soon too.

Post by **Robin1** » 11 Jul 2007, 12:39

GOOD LUCK!!

FoulOleRon · Post by **FoulOleRon** » 16 Jul 2007, 23:16

What's the news with these? Any further progress?

Post by **Panteneman** » 17 Jul 2007, 07:59

I have good reason to believe that Fez was able to RX NTJ, from who is based down in the midlands for a week or so because of work. He was TX'ing from some apartment block somewhere.

I am reliably informed that there is still a SWR related issue, but results appear to be shockingly good.

I wouldn't mind getting one of those Chinese imported UHF handhelds for this kind of thing. This UHF DX'ing seems fascinating, I am a fan of PMR446. More frequencies to play about with that are licence free, a good thing in my book

Good on them, I say...

Post by **fez** » 17 Jul 2007, 08:33

nonono, I rxed him from his house 19 Km from my house the day before he went there, NTJ (aka Iain) is currently on work in coventry and is going to try some contacts from the midlands from the top of his hotel window etc on 446.