Homebrewing a Sirio Gainmaster using RG58 and 2.5mm wire.

[Kaos]

What are the thoughts on using a T Piece and 259's for the stub attachment?

I see now reason why it wont work TBH.

Thoughts?

[PsiDOC]

That will work fine.

Psi

[Stronty]

Yep that's what i'm now going to do on mine, what clicked for me was watching Dave's Vid on the Quasar .64 seen Here at around 1 min 23sec, nice and easy when you think about it, or someone else does for that matter.!

[Kaos]

Just bought them and they are fitted.

Just a last few bit to do then its gonna get a run tonight.

[Kaos]

Right just back from town as the youngest daughter won something in a toy shop.

Anyways here are the findings:

Using a Lincoln with about 30w going thru it.

26.000 - 2:3
26.500 - 2:1
27.000 - 1:9
27.500 - 1:6
28.000 - 1:4
28.500 - 1.3
29.000 - 1.2
29.500 - 1.3
29.999 - 1.5

All the coax is RG214/U and the stub is joined together with a T piece and 259's. The top braid is pure copper at about 2mm thick.

While there is not alot of EU FM activity round here I did notice a huge drop of static. I used my IMAX2K to compare it with. The GM is on the ground just now (dark) but I did here low USB on 555 clearer on the GM than the higher IMAX2K. S points were out the window due to the noise/static.

Just caught the back end of Russian truckers on AM and again both came in with same result as SSB.

I suspect the stub is a little short as the centre freq appears to be about 29.000, so I will look at the the morra.

The coax feeding the GM was RG58/U.

Now whether or not it has the same characteristics as the real GM that remains to be seen. Saying that, all the measurements that Psi has helped with/figured out work, meaning the AE is usable.

Looking fwd to getting it up on the roof then having a proper fight out with the IMAX2K.

Pics to follow when its light.

[PsiDOC]

Actually I'd say the stub is a little long. The phenomeon with the stub is that shortening it raises the swr curve in the higher frequencies and reduces it in the lower frequencies. Anyway you have nothing to lose by shortening it so try cropping off 1cm and do another sweep.

Psi

[vkrules]

In theory it's just a 5/8 and should not be any better or worse that any other 5/8. In practice I find it's significantly better than my imax with long distance dx I.e 2000 km and about the same with locals and short skip but with lower noise. I think the gm does indeed produce a cleaner low angle radiation pattern than other 5/8 s , as claimed by Siro. Most verticals suffer from the pattern skewjng due to current on the mast and or coax The gm is well isolated and this is less of a problem .When constructed with 214 or 213 it could well be better that the original siro with better high power rating and lower loss. An interesting test would be to insulate the imax from the mast and wind the same choke at the feed point!

[vkrules]

Actually I'd say the stub is a little long. The phenomeon with the stub is that shortening it raises the swr curve in the higher frequencies and reduces it in the lower frequencies. Anyway you have nothing to lose by shortening it so try cropping off 1cm and do another sweep.

Psi

True but I found if the other end is to short( between aerial and t) it also produces that sort or curve. Ain't trial and error wonderfull.

[PsiDOC]

It is indeed. Basically the antenna was made using good old trial and error.
Although it's a lot easier to trim the stub than the antenna to achieve a good match.

Psi

[Kaos]

MMMMMMMM.

Trimmed the stub by 5mm and started to blow fuses in the lincolns power lead. Not happy.

Anyways before the trimming I worked 110 and 291 (Cyprus) and heard alot more.

Might have something to do with the drizzle. Need to waterproof it when finished.

Still it works.

[Stronty]

Sounds like you are having fun Kaos!

I'm now tempted to purchase one of those cheaper Antenna analysers on the back of this.

great thread.

[Kaos]

Its been up at same height as my IMAX and I intended to do lots of comparisons with the IMAX, but as soon as I put out one shout on 385lsb and a couple on 025am time flew by.

Using 150w (Amp) and 25w from Lincoln it worked about 2 dozen US stns and a few in the Caribbean. All with good radio n signal reports.

Have arranged with locals to do a decent test with the 2 the morra.

As for the feed point being 50 OHM or if it acts like a GM, who knows. I do know it works.

Will get pics up the morra of each bit before I finalise it and waterproof the exposed bits.

Might have to do the same as you Stronty and get a cheapo Ae Analyser. Any suggestions?

[Stronty]

The ones I have read about are mostly copies of or similar too what is talked about Here

From ebay these,

Northern35 may or may not have got one from here

Another variant

There is also a thread on TM1 Good detail in this one

[Kaos]

Here is a YouTube vid of my GM

http://www.youtube.com/watch?v=AGyH0kJkbRk

and here is a vid of the GM and IMAX on RX.

http://www.youtube.com/watch?v=tBsZ9FzPSP0

Overall chuffed to bits with performance. Less noise on GM than IMAX.

[PsiDOC]

For the few £££'s it cost to make without the price of the fishing pole it really is a surprising performer isn't it.
Watching your vid on ewe tube it looks like the Imax just had the edge on RX but as you pointed out there was a 2 s-point difference in noise which can be all the difference. Definately all good.
Did you sort out the blowing fuses issue?

Psi

PS: As a footnote those clone Sark antenna analysers that stronty was mentioning look good value. You pay £119 for a basic bare bones MFJ207 that only does to 30 mhz and has no display so you need to plug in a counter.
If I didn't have my modded MFJ 209/259B hybrid I'd be looking at one for myself.

Psi