Homebrewing a Sirio Gainmaster using RG58 and 2.5mm wire.

[PsiDOC]

Hi Eddie.
Yes you understand correctly. When I was finding the correct point to attach the stub I used the strip connectors (screw terminals as you called them) as it was the easiest way to adjust whilst working on the antenna. On the finished design I actually removed the strip connectors and soldered the 3 centre cores, then 2 layers of heat shrink tubing to insulate them, then soldered the outer shields together and again heat shrink tubing to insulate / weather proof. A lot more permanent that strip connectors.

You should really keep the upper part straight as intended. Can you extend your fishing pole with some bamboo cane perhaps?

I have modelled the antenna using 1mm wire and there is a little difference. Although how this would affect the real world performance I do not know.

Cross needle SWR meter will do nicely.

Set and forget. Once you have built it using the dimensions I have given you should be good to go. YOu may need to trim the stub a little.

Psi

Hello, newbie here.

I'm pretty new to this hobby and don't really have the theories behind all this in my head, but I've tried to read and learn as much as I can in these last few months.

So I began looking around this project and came up with some questions, if you don't mind.


Did I understand correctly, that you cut the coax at 218,5cm up from the choke, and connected the stub and the upper part of the coax to the lower part with a screw in terminal? (Forgive my lack of knowledge on the technical terms, English is not my native language and my skills are rusty.)

Due to the season all I have and can get at the moment is 6m telescopic fiberglass fishing pole to use as a mast. How would it affect the performance, if I wound the wire above the capacitor, or the whole thing for that matter, loosely around the pole to match its length better?

How much difference it would make if I used different than 2,5mm2 wire for the upper part?

Can I get this antenna to work as expected with just a cross needle swr/power meter?

As I've understood, some antennas need to be tuned where they are/will be installed to work properly, and others can be tuned (pretty much) anywhere and don't need any further adjustments if they are installed elsewhere. How does this antenna work? Set and forget? Or do I have to tune it up every time I change the location`?


I hope I didn't ask too many (dumb) questions. Thanks for the informational post, this just the kind of stuff I've been looking for, and thanks in advance.

[Eddy]

Thank you very much for the answer(s). I think I can figure out something to add to my fishing rod, we shall see. I'll be sure to report my success when I get the project done.

[northern35s]

Now there's a project, a shorter GM, it won't be as efficient as a full size GM, but potentially a similar bandwidth, so the Spring project is an inductively loaded top section with a standard size lower section, 1/2WL height with near GM bandwidth, it'll sell in droves

[Eddy]

I got my gain master clone soldered together today. I will try to figure out the time and place to tune it up this weekend. I'm somewhat hesitant about the outcome, it may turn out to be a plain disaster of an antenna... I have already decided to make a new one no matter if this one works or not, practise makes perfect. At least now I have a clue what I'm doing.

[Stronty]

I have not had time yet to try this out but Eddy if you can it would be nice to see some pics of your construction technique, the stub etc i can see in my head but i wonder if it's totally squiffed! nice not to repeat other mistakes as such.

[Eddy]

I will see what I can do about the pics Stronty. If this version 1.0 works, I may take some photos and highlight (some of) the mistakes I made. If it doesn't, I'll pass the photos until v 2.0. By that time I hope I can avoid the mistakes I made today.

The stub connection was a bit of pain to figure out how to do, but I think I know now how I should do it next time. PsiDOC's last message above shed pretty good light for me about the connection (too bad I realised it after I had the work done...).

The good thing is, at worst I learnt a few things and threw away some tens of cm of RG58 coax and Aircell 7 (I didn't mention I used Aircell 7 for the stub, didn't I? Well, that's what I used. ). And the non-ruined parts of RG58 I can recycle as patch cables for SWR meter's etc. At best I may have got myself an antenna that takes less space in the car than A99 to take with me to peditions.

[Stronty]

Yeah thats the stuff! great.

I too will be using it for taking away, I've got one of those 10m telesopic Roach poles, so thinking i can feed it up inside and hold it there with a cork, leaving some of the smaller top sections out of course.

WA10 linked some pics i think to the stub somewhere, or i saw it on another site but must have forgotten to sticky them to my homebrew gainmaster folder.

[Eddy]

WA10 linked some pics i think to the stub somewhere, or i saw it on another site but must have forgotten to sticky them to my homebrew gainmaster folder.

If you remember where you saw it, please share the link.

[PsiDOC]

@ Eddy.
Glad you made it bud. OK some tips for you.
Provided you made the main lower part of the antenna from RG58 then the stub attaching point is correct at 126cm from the centre as the VF of the main coax used determines this point.
Using Aircell 7 your stub should be approx 72cm long, however I can see you trimming that down to about 70 - 70.5 cms when in place for tuning.
Let us know how you get on and please post / pm me if you run into difficulty.

Psi

[Eddy]

I will post my progress report when I get the time to go and try to tune the monster.

[PsiDOC]

Ah Taming the monster is not as difficult as you think.
with 72cms of Aircell7 stub you will be very close. Who knows? It may even be perfect for you.
So a Swr sweep from as low to as high as possible / legally allowed / as far as you dare go!
If you notice the swr is higher on 26 - 27 mhz than 28 - 29 then trim 5mm off the stub, short out and sweep again. You will notice the 26 - 27 portion has a lower swr now. However don't go too trim crazy! It will affect and drive up the 28 - 29 mhz portion SWR if you trim too short on the stub. YOu're looking for a happy medium.

Psi

[Eddy]

Brief update:

I got myself an 8 meter fishing rod in the mail yesterday. I took it apart and did the same to my old 6 meter rod. There was one element in the old one that I could use with the new one, bringing the total pole length to about 9m. So that got sorted.

Today I hopped in my car and drove to my parents' place. I had the pole, the antenna, 10m coax and a cheap swr-meter with me. I have basic cb-setup in my car (EU40ch cb, Sirio Turbo 2000, KL-203).

Putting the pole together took a little time and taping up the antenna to the pole took some time too. I raised the antenna and stuck it into a pile of snow that was handily close but not too close to my car. Hooked up the swr-meter and did a check on 26.965, 27.405 and then 27.205MHz with 4W.





SUCCESS!

The needle barely moved. That does not tell the whole picture though, as I don't completely trust the meters accuracy. But I trust it enough to hook up the KL-203 in its place. I did a little test with a friend in mobile about 20-25 km away and everything worked as it should.

No pics taken this time, it got too dark for that. Also it was cold, -21 Celsius and getting colder, so I had to go inside a few times to thaw my fingers.

Next up is checking the solder joints and insulations and finding the time to measure the swr outside the cb band with decent meter.

Not bad for a first try.

[northern35s]

Sounds like a great result Eddy

[PsiDOC]

Nicely done eddy. I had complete faith in you.
Welcome to the home made Gainmaster club.
Seeing as I am here I'll post a little update for you all. The Psi-GM™ is still up on the pole even after being beaten senseless by the high winds of the last few weeks which may I add it took without so much as a complaint.
I now use it as my main antenna for 10, 11, 12 and 15 meters (12 and 15 with a tuner) as it is simply better than my full sized G5RV on the above bands.
QSOs as far away as Argentina, Chile and Brazil to the west and India and Pakistan to the east. All done on 50 watts maximum power and the lowest signal report has been 5/6 into India.

I still think there's more to be gained from this antenna in terms of flexibility.
I am sure I can tune 12 meters into this antenna without trading off too much on the top of 10 by extending the radiators by a 30cm or so and reworking the matching stub. Obviously by lengthening the radiators there is a slight gain increase as well however it's only slight.
Also did I mention I have built a mini-me version for 6 meters that tunes from 48 - 57 mhz?

[Eddy]

Nicely done eddy. I had complete faith in you.
Welcome to the home made Gainmaster club.

Thank you!

I will begin working on v2.0 in the near future. This time I'll be sure to take pictures during the build and will try to take some during the tests too.

Also did I mention I have built a mini-me version for 6 meters that tunes from 48 - 57 mhz?

Ho-hum, I may have interest in scaling this thing to VHF (4m, 68MHz), any chance you could enlighten me a bit?

EDIT:
These are the frequencies I'm after:
68,050 MHz, 68,175 MHz,
67,500 MHz, 68,575 MHz,
71,375 MHz, 71,425 MHz,
71,475 MHz, 71,625 MHz,
70,200 MHz, 71,025 MHz,
71,050 MHz, 71,100 MHz,
68,375 MHz, 71,175 MHz,
71,750 MHz, 71,900 MHz,
71,350 MHz, 71,550 MHz,
71,575 MHz, 71,600 MHz
72,325 MHz