Homebrewing a Sirio Gainmaster using RG58 and 2.5mm wire.

The place to talk about specific radios, equipment and accessories. Do you prefer the latest generation of rigs and antennas or do you like the classics? Discuss it here!
Post Reply
User avatar
PsiDOC
Super Member
Super Member
Posts: 446
Joined: 16 Aug 2011, 18:39
Call Sign: 163FKU
Location: Moonbase Alpha
Contact:

Homebrewing a Sirio Gainmaster using RG58 and 2.5mm wire.

Post by PsiDOC » 03 Jan 2013, 21:15

REV2: Updated 15:20 04-01-13

Evening all.
Am reporting here my findings on my latest project. Homebrewing a Sirio Gainmaster antenna using commonly found bits and bobs found in the shack.
Did it work? A tentative yes. It tunes - so the theory holds up well and is quite forgiving. Proper field testing will be done on the weekend as I ran out of time today and sadly I am in work tomorrow.

Introduction:
The Sirio Gainmaster is a broadbanded 5/8 wave centre fed "sleeveless" sleeve dipole antenna. A sleeveless sleeve antenna is defined as a sleeve antenna that uses the parasitic common mode current on the outside of the shield in the coax as the lower half of the dipole. To stop the rest of the coax radiating and causing tuning issues a choke is immediately placed after the desired length of the lower half of the dipole to eliminate any common mode currents getting further back down the feeder coax and back to the shack.
Broadbanding:
An 8.6 PF Capacitor is used at the base of the upper radiator to give a useable tunability of between 25.5 to 29.6 mhz This is a unique feature of this antenna.
Matching:
A 5/8 wave antenna has a feed point impedance of approx 200 ohms this for us 50 ohm users equates to a VSWR of 4 to 1. Niether use nor ornament. So a shorted matching stub is placed in the feedline approximately 1.91 meters multiplied by the coax velocity factor below the centre (feed point) of the antenna to match to a palatable 50ish ohms. This again is a unique feature for a sleeved antenna.

Some musings about the matching stub and the attaching point.
I found the match point the old way. test, adjust, test (lather, rinse repeat). However once I had the match point I was able to crunch some numbers regarding the match point.
The Match point of the stub is 126.5 cm away from the feed point using RG58.
This multiplied by the coax velocity factor (0.66) gives us the free space distance which is 191.666666667 cm
Now consider this:
Using the original match point of 149.5 and dividing it by 191.666666667 gives us the velocity factor of 0.78 for the original coax used by the Original Manufacturer of the design.
I know that RG8X can be bought with a VF of 0.78 and with a solid core centre element. So I wonder if that's what was used in the original? Food for thought.

Conversely this also means that if using a different coax with a different velocity factor (VF) you can calculate the matching point connection using the formula: 191.666666667 * VF.
EG: RG303 with a VF of 0.7.
191.666666667 * 0.7 = 134.166 cms from the centre feed point.


Stub length can be calculated from the original as we know that Rg303 was used for this and thus:
59.5cm / 0.7 vf = 85
For our RG58 Stub with a VF of 0.66:
85 * 0.66 = 56.1 so our stub length is 56.1 or there abouts. Simply trim this to get the best match. Mine trimmed to 55cm.

Construction:
Below is a picture of the actual dimensions of my freshly fabricated poverty spec Gainmaster. This was using Belden MRG5801 (the new name for RG58 from Belden) and 2.5mm (14AWG) stranded insulated copper wire for the top half of the antenna.

Image

Walking through the construction from bottom to top:
Coax Choke: Find a former 66mm in diameter. Wind 16 turns of coax on it and secure it properly and tightly. If you have used a conductive former remember to remove it. Then Do not cut the coax! Measure a length of coax 360cm from the top edge of the Coax choke. This is where you want to cut it.

Matching Stub:
Measure a length of Westflex 103 coax 75 cm and cut it. Now strip one end 25mm so that you have the centre core and the shield seperated into 2 tails. You need to attach this centre core to centre core and braid to braid at a point 218.5 cm up the coax from the top edge of the coax choke. How you attach it is up to you. I prefer the cut and splice method personally. If you feel that 25mm of tail s is too long feel free to trim them to suit your build. Just remember to keep 72cm of coax untouched as this is the business end of the matching system.
On the unattached end of the matching stub strip it back 5mm and short it out braid to centre core and tape it downwards to the main coax.

Coax Capacitor:
Measure up the main coax from the top edge of the coax choke 345cm. Now mark this point. A further 2.5cm up the coax mark again. You need to strip away the outer sheath and the coax braid between the 2 marks.
Now measure up again 8.64cm from where you have stripped away the coax and strip the outer sheath away. Split the shield and twist back to form a solder tag. The inner coax core that is protruding can be trimmed flat but leave 6mm or so protruding from the end. Insulate and weather proof the centre core.

Image

Top Radiator:
Solder a length of 2.5mm wire to the solder tag you created. Now measure 345cm from the centre point of the antenna (The point where we stripped 25mm of the sheath and braid) and cut the wire.

Now erect the antenna on your favourite non conductive pole and tune by trimming the end of the matching stub and shorting it out again.

when you're happy, weatherproof. and attach it permenantly to you favourite non conductive pole.


Tuning:
Here are the results from my trusty MFJ antenna analyser.

25.6 Mhz

Image
A bit low ohms wise but still within the 2:1 limit

27.5 Mhz

Image
1.3:1 Just where I like it.

28.5 Mhz

Image
1.1:1 To be honest I expected the lower ratios to be a bit further down the band. Hmmm

29.6

Image
1.6:1 It's worth noting that the broadband VSWR curve shoots upwards a lot quicker at the upper end of the frequency as the antenna become too long.

And Finally:
A shot of the antenna in the test location.

Image

As a foot note all pics and hi-res available here: http://www.psidoc.com/gainmaster/

Hope this is of use to anyone.

Psi
Last edited by MrWeetabix on 13 Jan 2013, 21:09, edited 8 times in total.
Reason: Matching Stub info updated at poster's request
*Proud owner of a Cornflake Packet Amateur License and registered instructor in the art of gaining said license*
Icom IC-756 Pro III
Yaesu FT100D.
President Washington
President Adams
Tait T2020 70mhz
Baofeng UV-5R 2m / 70cm

FAFFER
Super Member
Super Member
Posts: 286
Joined: 17 Feb 2012, 19:01
Location: Stockport

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

Post by FAFFER » 03 Jan 2013, 21:30

Awesome!

Have you got another antenna to compare it against? As in, a silver rod at the same qth...
Build a man a fire, he'll be warm for a night. Set a man on fire and he'll be warm for the rest of his life.

User avatar
PsiDOC
Super Member
Super Member
Posts: 446
Joined: 16 Aug 2011, 18:39
Call Sign: 163FKU
Location: Moonbase Alpha
Contact:

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

Post by PsiDOC » 03 Jan 2013, 21:37

The only thing I have is G5RV deriative (ZS6BKW) running east / west. On 10/11m it gives 4 defined lobes of about 5dbi towards Lower North / S.America and Norway and over the middle east. This is the only base point I have and I will be using it.

Psi
*Proud owner of a Cornflake Packet Amateur License and registered instructor in the art of gaining said license*
Icom IC-756 Pro III
Yaesu FT100D.
President Washington
President Adams
Tait T2020 70mhz
Baofeng UV-5R 2m / 70cm

User avatar
crusty
Veteran
Veteran
Posts: 3229
Joined: 02 May 2008, 18:28
Location: East Lancs. UK

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

Post by crusty » 03 Jan 2013, 22:41

Nice work. What did you use for the the tapered antenna sleeve ?

User avatar
Irishman1127
Moderator
Moderator
Posts: 4444
Joined: 23 Jan 2011, 12:34
Call Sign: EI7KO
Location: Central Ireland

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

Post by Irishman1127 » 03 Jan 2013, 23:07

Telescopic fibreglass pole I'd say....
CQ CQ CQ DX

User avatar
MrWeetabix
Admin
Admin
Posts: 14303
Joined: 26 Aug 2008, 13:34
Call Sign: 26TM175
Location: Tynemouth

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

Post by MrWeetabix » 04 Jan 2013, 00:13

Great work....... when can we buy them? :-p
26TM175. OP: Craig. QTH: Tynemouth. Also 163TM175 when mobile in Wales 8)

PO Box: 62 Town: Albrighton City: Wolverhampton Zip: WV7 3WR

TM1 is now on Facebook http://tinyurl.com/TM1onFB || New Tango Mike QSL cards https://tinyurl.com/TM1-NewQSL

User avatar
PsiDOC
Super Member
Super Member
Posts: 446
Joined: 16 Aug 2011, 18:39
Call Sign: 163FKU
Location: Moonbase Alpha
Contact:

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

Post by PsiDOC » 04 Jan 2013, 06:22

crusty wrote:Nice work. What did you use for the the tapered antenna sleeve ?
29GD01 is right on the money. It's an ebay special 10 meter fishing pole that cost £25.
Also bear in mind the antenna will be always be cable tied to the outside of the pole. Trying to get it inside with the coax balun outside will weaken the pole. Weather proofing it externally shouldn't be a problem anyway.
MrWeetabix wrote:Great work....... when can we buy them? :-p
From me? Probably never mate. I'd rather fire up peoples creativity. A couple of hours work with some wire and coax and you can make your own. The hard work - finding the correct point for the matching stub - is done for you. ;)

Will post full construction details later today. Off to work in a moment sadly. :(

Psi
*Proud owner of a Cornflake Packet Amateur License and registered instructor in the art of gaining said license*
Icom IC-756 Pro III
Yaesu FT100D.
President Washington
President Adams
Tait T2020 70mhz
Baofeng UV-5R 2m / 70cm

User avatar
crusty
Veteran
Veteran
Posts: 3229
Joined: 02 May 2008, 18:28
Location: East Lancs. UK

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

Post by crusty » 04 Jan 2013, 11:36

Ah, wondered what the banding (tape) was.

User avatar
Ashtec
Legend
Legend
Posts: 9157
Joined: 30 Dec 2009, 23:12
Call Sign: M6LTD
Location: Uk

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

Post by Ashtec » 04 Jan 2013, 11:40

Intresting ;)

Good work!!!

User avatar
PsiDOC
Super Member
Super Member
Posts: 446
Joined: 16 Aug 2011, 18:39
Call Sign: 163FKU
Location: Moonbase Alpha
Contact:

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

Post by PsiDOC » 04 Jan 2013, 15:25

crusty wrote:Ah, wondered what the banding (tape) was.
merely insualtion tape that I had handy to attach the antenna to the pole. ;)

Psi
*Proud owner of a Cornflake Packet Amateur License and registered instructor in the art of gaining said license*
Icom IC-756 Pro III
Yaesu FT100D.
President Washington
President Adams
Tait T2020 70mhz
Baofeng UV-5R 2m / 70cm

wa10
Top Poster
Top Poster
Posts: 1170
Joined: 19 Feb 2008, 00:37

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

Post by wa10 » 04 Jan 2013, 17:06

nice work psi, glad you got it working ;)

User avatar
bigpimp347
Legend
Legend
Posts: 8416
Joined: 08 Aug 2009, 10:23
Location: J26 Nottingham
Contact:

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

Post by bigpimp347 » 04 Jan 2013, 17:46

good way to save a few quid..
i made a double bazooka and am thinking about sticking it inside a plastic tube,
same could be done for a psiDOC gainmaster simple plumbers pipe and some joints and sealer and you have a pretty sturdy aerial..
http://livecbradio.co.uk UK's only 24/7 live stream

User avatar
PsiDOC
Super Member
Super Member
Posts: 446
Joined: 16 Aug 2011, 18:39
Call Sign: 163FKU
Location: Moonbase Alpha
Contact:

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

Post by PsiDOC » 04 Jan 2013, 18:17

Gainmaster indeed ya cheeky **** Mark!

Although, yes you are correct, although at 24 feet tall the pipe and end connectors would have to be very sturdy.

Psi
*Proud owner of a Cornflake Packet Amateur License and registered instructor in the art of gaining said license*
Icom IC-756 Pro III
Yaesu FT100D.
President Washington
President Adams
Tait T2020 70mhz
Baofeng UV-5R 2m / 70cm

User avatar
PsiDOC
Super Member
Super Member
Posts: 446
Joined: 16 Aug 2011, 18:39
Call Sign: 163FKU
Location: Moonbase Alpha
Contact:

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

Post by PsiDOC » 06 Jan 2013, 10:24

HI all. Just a follow up on the build.
The antenna has been up since friday night, however as usual the upper portions of the band were closed yesterday with nothing heared on my main antenna or the homebrew. Sadly local 27mhz around here is as dead as a dodo and has been for a couple of years now. So no local contacts to test with either.
Due to mother nature not being on my side yesterday I did some TX tests and then tried the antenna on some lower bands with a tuner.
TX Tests.
Burn in test: 100 watts dead key on 28.250 for 5 mins - No flashovers and no fluctuations in SWR.. I think we can call that a pass.
Swr tests @ 100w, antenna 2.8 meters above ground:
25.5: 1.9:1
26.0: 1.3:1
26.5: 1:1
27.0: 1.1:1
27.5: 1.4:1
28.0: 1.4:1
28.5: 1.1:1
29.0: 1:1
29.5: 1.4:1
30.0: 1.9:1

Interestingly I now have the double null in the swr curve that the original has, however when I was testing with the MFJ at the feed point I was not getting this, which puzzled me a bit. I guess the feedline has some bearing on this.

Common mode current (rf on the feedline) test @ 100w:
Zero, nil, nada, nothing. The coax choke seems to work well!

21mhz test @ 2.8m above ground.
Seeing as the 12, 11 and 10 meters were lifeless I thought I'd try my luck with it on 15 with the tuner. Bearing in mind on 15 the antenna is approx a 1/2 wave so it should work reasonably well.
I does indeed work with a few contacts into Russia, namely moscow on 50 watts with the obligatory 5/9 so after explaining I am testing the antenna and would they be so kind as to recheck the signal report, a more realistic 5/6 was reported. They were 5/7 to me as at 100w.
So... it's not a dummy load and it does work even a bit out of band.

Today's testing @ 2.8m above ground:
Finally 11/10 are open a bit!
Currently working eastern europe with repeated 5/9 (why do people do that?) and when asked to reconfirm am getting 5/6 reports using PSK at 20w. Switching to the wire antenna these reports are about the same or slightly higher, however I am getting a fair bit more noise from the wire.
More testing will be done through the day.

Whilst I appreciate comparing with a wire it like trying to compare an apple with an orange, however it's all I have here to do any comparisons with. Also consider the wire is 8 meters above ground at the feedpoint and the Gainmaster is 2.8m at the feedpoint

All in all a successful project I think.
Made for less than £12 in materials and a glassfibre fishing pole that I had in the garage.
If you wish to factor in the cost of the fishing pole it was £25.
Sirio Gainmaster for less than £40 anyone? :)

Psi
*Proud owner of a Cornflake Packet Amateur License and registered instructor in the art of gaining said license*
Icom IC-756 Pro III
Yaesu FT100D.
President Washington
President Adams
Tait T2020 70mhz
Baofeng UV-5R 2m / 70cm

Windy_Miller
Top Poster
Top Poster
Posts: 1290
Joined: 08 Jan 2007, 23:46
Location: Scotland, far North

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

Post by Windy_Miller » 06 Jan 2013, 12:26

So the design is not rubbish after all, as some tried to make out when they first came out? ;-)

I guess like so many other projects, the economics can very somewhat if the manufacturing time is taken into account, and whether or not things you have "commonly lying about" are the same as others have too. Being self employed, if I took the time it takes to make one into consideration, it would cost more than buying one. Put another way, it would be more cost effective to be out making money, then spending some of that money on buying one which has been mass produced, faster and using less man hours than I could ever hope to achieve.

Anyway, its good to see that all the initial scorn and ridicule that was poured on this product and its design when it first arrived seems to be melting away, and I read in other threads here that they are becoming popular in some areas, and even the antenna of choice! Pretty much mirrors the ridicule that the Chinese designed and made radios got when they too first came out - Now, you can hardly look at a signature file radio listing without it containing Anytones or Baofengs!

Post Reply

Who is online

Users browsing this forum: No registered users and 7 guests