Homebrewing a Sirio Gainmaster using RG58 and 2.5mm wire.

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Kaos
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Re: Homebrewing a Sirio Gainmaster using RG58 and 2.5mm wire

Post by Kaos » 18 Dec 2013, 18:44

Still got mine up in the air.

Loving it.

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Re: Homebrewing a Sirio Gainmaster using RG58 and 2.5mm wire

Post by CBCharlieST » 18 Dec 2013, 21:26

PsiDOC wrote:Very impressive indeed. I agree on the stub trimming methodology. If it gets to the stage where no difference is made then you have hit the right spot. Interesting that you had to add to the upper radiator to get a flat swr on the FCC part of the band. Every time I have done this it's pulled it downwards towards 26.7 mhz as I would expect.
What wire did you use for the upper radiator?
Would there be any chance of posting the swr readings from 25.5, 25 and 24.8 mhz please? I am just wondering if you can hit the 12 meter band with it.
NO mater though, well done on getting it as you want it. Now get it up in the air and see how it perfoms :)
Another homebrew gainmaster on the air. I love it!
When I started building the GM thought I was going to get some normal, everyday SWR of 1.4-1.5 through as you say the FCC band, but this did not expect it!
I think a lot of importance has matching stub or material of which it is made.
That's what you were experimenting with changing RG58 for westflex
This Belden H400 is a solid piece of coaxial cable as hard as a wooden stick, and I think he does a great job of reasoning antenna attached along its entire length for thin coaxial lower part of GM.
- For the upper radiating element I used a 2.5mm square stranded wire, means a sectional diameter of about 1.7mm.
-No problem, next week between Christmas and New Year when I borrow an instrument and I will do readings for 12m band.
-Today I made some tests here in the local receive better for two to three units. I talked to a guy from the city of Baghdad, and I noticed that the antenna reception has a lot of white noise and it is interesting that the noise is slightly reduced by the addition of one extra piece of wire 25cm! which means that the antenna resonates well in the air.
When I have more time I will replace the wire from the top element with pipes made of brass 2mm diameter, this turned out to be very good when I did a double bazooka.

This is great that you published method and idea for making homemade GM every honor to you PsiDOC
greeting.

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Re: Homebrewing a Sirio Gainmaster using RG58 and 2.5mm wire

Post by CBCharlieST » 18 Dec 2013, 21:40

JGR wrote:Looking good and how are you finding it performs also what are you comparing it too?
Also photo P1010008.JPG looks like there is a UFO in the picture :lol:
for now it does not compare with anything, and for the future with lafayette CBS-18 and gp Lemm ... we'll see.
:D That looks like a UFO but it is still an air rat - seagull

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Re: Homebrewing a Sirio Gainmaster using RG58 and 2.5mm wire

Post by vkrules » 26 Dec 2013, 02:40

Mine is still in the air as well.

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Re: Homebrewing a Sirio Gainmaster using RG58 and 2.5mm wire

Post by 43cs44 » 16 Jan 2014, 08:18

Hi guys , great thread going here , has anyone got a set of dimensions to start with for the 6 metre band ,50-54 Mhz,
I havent quite figureged out the formulas used. , I will see if I can get it working there b4 making the bigger version.
Thanks.

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Re: Homebrewing a Sirio Gainmaster using RG58 and 2.5mm wire

Post by 43cs44 » 27 Jan 2014, 00:32

So after a few days of calculations and uneducated guesses I have come up with these dimensions for 6 meters
using rg58 for the feed and rg213 for the stub and capacitor
design freq 50.0 MHz
choke 13t on 50mm former,
or 9t on 66mm.
top wire 1875mm
feedpoint 687mm from center
stub 307mm
capacitor 5.0pF = 49.8mm (guess)

how do these numbers sound ?,
and is there a formula to actually calculate the correct capacitance by frequency?

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Re: Homebrewing a Sirio Gainmaster using RG58 and 2.5mm wire

Post by vkrules » 27 Jan 2014, 02:08

Ok here are My figures Freq 52 mhz
choke 8 turns on a 66 mm former
top wire 1880
feedpoint 640mm
stub 310 mm
cap 43 mm
My swr 1.5 points are 55 mhz and 49.3
swr min 50.3 1 to 1
rg213 used for stub

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Re: Homebrewing a Sirio Gainmaster using RG58 and 2.5mm wire

Post by vkrules » 27 Jan 2014, 03:07

Hi just like to add ,I threw this together in about 2 hours and stuck it out the window on a fishing pole , haven't spent any time fine tuning yet or getting any reports on air . The stub might be a little long I started long and trimmed it suit.Also I am getting the characteristic second dip in the swr at 53.5. and no cmc evident .I think it's good to go.I don't think anything is to critical in the build.

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Re: Homebrewing a Sirio Gainmaster using RG58 and 2.5mm wire

Post by 43cs44 » 27 Jan 2014, 09:14

well my first attempt was out a fair bit
it came in at 1.1 on 47.5 rising to 1.5 on 51.5
i would have expected it to be higher than this.
First i will reduce the capacitor and ff that fails some pruning may be in order.
or perhaps a longer stub
Too hot here to get too energetic !!
2 vkrules , how did u t in ur stub?

Back to the drawing board

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Re: Homebrewing a Sirio Gainmaster using RG58 and 2.5mm wire

Post by vkrules » 27 Jan 2014, 21:41

Off course you can us a t piece and three connectors .But my method for the t is to take off about 4 cm of insulation and cut the braid around the middle about 3/4 around the cable ( leaving the back of the cable intact)and fold it back, you will need it later,I then remove a 3cm piece of the dielectric exposing the centre conductor , careful not to cut the cable all the way through I then use a small screw driver to open a gap between the centre conductor and remaining dielectric and solder the centre conductors . I melt some scrap dielectric for insulation over the joint.Now pull back that braid that you folded back and solder together with the braid of the the cable your splicing in, cover with rubber tape.
This way is a lot easier than trying to join 3 pieces of cable and the joint is quite strong.Before you cut anything fold back some of the top wire on it's self and test again.

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Re: Homebrewing a Sirio Gainmaster using RG58 and 2.5mm wire

Post by 43cs44 » 28 Jan 2014, 07:07

got home from work today , 45.6 deg c in the shed.
no probs , cut the capacitor off and made a new one at 43mm
also fine tuned the sections back to 1875 and cut the gap below the capacitor to 10mm
it now shows 1.1:1 at 50.150 MHz rising to 1.5:1 at 54.000 MHz
I'm gonna be satisfied with that , now to plan getting it inside the squid pole.

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Re: Homebrewing a Sirio Gainmaster using RG58 and 2.5mm wire

Post by PsiDOC » 29 Jan 2014, 11:21

Sorry guys, only just seen this.
On my 6m one I used:
Upper / lower radiators of 2 meters long.
Stub attaching point: 73cm below centre point.
Stub length: 36cm @VF of 0.86 (RG213, W103 etc)
Choke: 8 turns at 66mm diameter.

Swr plot attached.

Now bearing in mind that here in the UK we only have 50 - 52 mhz I built it long to suit the bandplan.
Although even with those dimensions I am sure I can twiddle the stub arrangement to drop 54 mhz into the equation.

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Re: Homebrewing a Sirio Gainmaster using RG58 and 2.5mm wire

Post by Kaos » 29 Jan 2014, 14:18

Just bought a 7m pole with the intention of putting the GM inside it.

I assume this will be OK as the IMAX and A99 are encased in fibreglass.

I want to make this a more permanent feature. Its quite ugly just now.

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Re: Homebrewing a Sirio Gainmaster using RG58 and 2.5mm wire

Post by vkrules » 30 Jan 2014, 08:09

Trouble with putting it inside a blank is you have to drill a hole, which will weaken it somewhat. I Just taped it to the outside and learned to live with it. Just built a second 6m GM just for the hell of it. This time I used Stub point of 70Cm ( this doesn't seem to critical).Stub came out again at 31cm. ( 31 is the money)Cap again at 43 mm. Tried adjusting the spacing of the cap ,that had very little effect. so I put it back at 25mm And I used 1880 again for element lengths. Happy with this one too .1.5 to 1.5 swr points are 5 mhz apart , but this time the double dip is very shallow.Got a chance to try it on air The tablelands beacon was coming in today and was as strong on the Gm as it was on my 3 el horizontal beam . Then got a brief opening into JA .Signals 1 1/2 to 2 s points down on the GM ,which is what I would Expect. I don't have another vertical to compare to.Anyway the GM is not a dummy load

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Re: Homebrewing a Sirio Gainmaster using RG58 and 2.5mm wire

Post by vkrules » 31 Jan 2014, 01:31

Hi psidoc can you do me a favor?, disregarding the swr curve,can you check with your software at what point the radiator becomes to long for 54 mhzs and starts to degrade the low angle of take off. Also have you compensated for plastic coated wire in your model. Text book tells us that over .64 wave lengths the pattern degrades with high angle lobes

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