Homebrewing a Sirio Gainmaster using RG58 and 2.5mm wire.

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

Post by GoldVolvo »

PsiDOC wrote:
09 Nov 2018, 20:39
MY goodness.
Is this thread still alive?
I am humbled.
Yes this fantastic thread is still alive and well it would seem. I'd just like to echo others and say a big thank you for providing the build info and dimensions etc. Currently using a T2LT made of RG58 and speaker wire but when I get another roll (soon I hope) I'll certainly be giving this build a go & possibly making it a more permanent fixture than the current home base setup of 30' of random wood and a tree branch taped together & tied to the fence post! (I'm cheap though, so will probably wait till a good long roach pole comes through auction and try and get one for a fiver!)

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ch25
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Re: Homebrewing a Sirio Gainmaster using RG58 and 2.5mm wire.

Post by ch25 »

Any chance to update dead links in OP?
Chris
You can't have too many antennas...

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

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ch25 wrote:
02 Nov 2019, 19:18
Any chance to update dead links in OP?
Chris
Agreed, by the way Lem' have you seen your post count? :D :twisted:

VK5LTD
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Re: Homebrewing a Sirio Gainmaster using RG58 and 2.5mm wire.

Post by VK5LTD »

I came across this antenna project after seeing a link on QRZ. 10m is lively during summer in Australia and a home brew 10m antenna for my beach house at Goolwa would be useful. Original pics/links are gone- did anyone save these? Will also check youtube. 73 Vk5LTD

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

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PsiDoc's photos I think are these ones.
coax capacitor.JPG
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Stronty
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Re: Homebrewing a Sirio Gainmaster using RG58 and 2.5mm wire.

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

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26TC62
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Re: Homebrewing a Sirio Gainmaster using RG58 and 2.5mm wire.

Post by 26TC62 »

I've been thinking about knocking up one of these for a while - 99% of my operating is portable, and indeed it is "portable style" at home if I want to use anything more than an Ampro whip. In the field I have a homebrew "standard" 5/8 with a tapped coil and radials on a 10m fibreglass pole, and frankly stringing out wire radials is a faff. The aerial works fine but something radial-less and a bit more broadband is attractive - SWR gets up near to 2:1 at both ends of 11m and I do use both ends of it as well as the middle! I actually read about 60 pages of the thread on this as well on funkbasis.de earlier, with a lot of help from the Firefox Google Translate plugin. The thread there digressed into making a 3-el vertical Yagi using a T2LT driven element which has got me thinking!

I am going to pop into Nevada and pick up some Mini-RG8 and knock one up out of that to start with. Mini 8 is fractionally more lossy than RG213 but if the stub misbehaves, I have got a long run of Westflex kicking around in a storage unit somewhere. Mini 8 like Westflex is 0.8VF and 80pF/m so the stub tap-point and capacitor length will need to change from PsiDoc's schematic but the length of stub won't. Mini 8 is a bit better than RG58 and I refuse to use that stuff for anything.

26TC62
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Re: Homebrewing a Sirio Gainmaster using RG58 and 2.5mm wire.

Post by 26TC62 »

Well I got a good length of Mini 8 in anticipation of needing to get through a bit to produce a working antenna. The dimensions I've got at present are:

Top section of wire - 3.52m
Capacitor - 10cm (Mini 8 is quoted at 80pF/M)
Length to stub - 1.53m
Stub length - 71cm
Stub join to choke - 1.99m

So this gives the two "halves of the dipole" both at 3.52m. I started off with 3.45 halves as per the usual dimensions, but starting with the stub at 72cm (Mini 8, like Westflex is 0.8 velocity factor) the antenna was tuning too high up for me - minimum SWR was well above 28MHz. I trimmed the stub by about 5mm and it shifted down a bit, but not much, and then another 5mm and it brought the lowest SWR down to 27.9MHz

At this point I thought I'd try a bit more length rather than keep trimming the stub (I was worried of over-pruning the stub, and having to remake the antenna when I wanted to get out portable with it the next morning), I'd lengthen the elements. Having done that, to the above dimensions, I got the SWR curve in the image (taken from a Rigexpert AA35).

As you can see, I'm not getting the broad "W" curve but a very good match where the HF dip is and should be, and a slight "shoulder" where the LF dip should be - around 26MHz on the SWR plot. The 2:1 points are 24.9MHz and 29.05MHz or thereabouts. I haven't had a chance to do proper A/B testing against my homebrew 5/8 but looking at the S-meter on my local WebSDR, the level is about the same as the 5/8 is. I didn't put the 5/8 up when I was out as it was wet and windy, and I was hiding under my tarp chasing the DX! The weather is going to be better this weekend and I hope to get the chance.

Eventually I am going to make one of these up in RG213 with Westflex for the stub, but what I thought might be something that ended up needing considerable rework because I am using Mini 8 is already working well enough that there is not much hurry to do it.
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