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Sirio Gainmaster Halfwave

J

JFC Kent

New Member
Mar 12, 2021
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I hope someone can help. I am about to install an old setup I have had not used for about 20 years and have so but the recpection is poor. So I purchased a Sirio Gainmaster Halfwave and want to get it mounted on the roof.

The only thing is I am confused as to where I should cut the antenna wire. In the documents it mentions cut 1783mm for 27.5MHZ which will do me. The anntena comes with one part already installed and then there is a joint that connects both together.

I know the 1783mm can not be the full lenght of the wire so must be the second half. Sirio dont make this very clear. So should I measure from the start of the connector at the antenna phase center. Or Should I measure 1783mm from that start of the black lead of the wire?

Please see attached photo.

gmhwwire.jpg


Image

PDF manual.
https://www.moonraker.eu/downloads/dl/file/id/358/product/3772/gainmaster_hw.pdf

Thanks JFC
 

The center of the antenna is where red coax stops & the black wire starts on the small pcb under the black heatshrink,

The chart is only a guide, Where you mount the GM will effect what length it needs to be,

Best method is put it up where its going to be used & check vswr then trim the black wire a little until minimum vswr moves up to where you want it.

if that's too much messing around measure from where you can feel the end of the red coax under the heatshrink,



Make sure you leave a little slack in the wire to allow for bending in wind.
 
Thanks Bob

Yes I need to orginise a lift to the side of the building, access isnt that good. Height is about 36ft to roofline and then I have a 9ft mounting pole. So expect to 5-6ft above roof line. So should be good I hope. Once this is up its staying up as the lift hire is quite expensive and I can only cost for one visit.

Wire dipoles and magmounts have been poor from this location. At least 3-5s of noise also tested with all the power in the house off on a battery. So I dont know what will happen. But important I get the best install I can with no messing about and see what happens.

Thanks for the info. As I say from the PDF the info isnt clear from Sirio but I do know a 27-28MHZ halfwave is at least 18FT and cutting 1783mm (5'8FT) just didnt add up to me.

JFC
 
Kent the L" length 1783mm is the length for the top two sections of the fiberglass...not the wire.

The triming of the wire is noted in Step #3 after the firberglass is set to the proper length for the antenna...at your frequency of choice.
 
Last edited:
Eddie is right,
the L sirio are talking about is the length you set each of the upper tubes,
the 1/2wave only uses 3 sections so its nowhere near the center of the antenna,

My buddy round the corner put a 1/2wave up & did not trim his,
when I asked him he said it was OK without trimming so I would not just chop the wire without at least making sure it needs it,

JFC good luck with the noise,
local generated noise is ruining the radio hobby for many people,

it is a pita when you can't get your antennas up and down safely without help,
I am in the same situation at the moment,
hopefully I will get something setup that I can raise & lower safely without help,

Big Kahuna, there's no trimming to do on the 5/8wave, its stub matched & very wide banded.
 
Yes thanks for the advice. Makes sense now :)

I slid the poles down each other to 1783mm for each which was 3566mm in total. I found that 130mm came off the wire after the adjustments. I dont really know what the center freq is by default but hopefully I will be near 1.1 swr on 27.500 where I plan to use SSB for DX and see what contacts I can get.

Will be a few weeks before I get it up. With regards to the noise yes there seems to be a lot. If it doesnt work out I guess I will put it back away untill such time I am in a good location.
But its been enjoyable playing about :)

JFC.
 
Bob, the 5/8 wave Gain Master does not give us a frequency chart for tuning, so it is cut to length at the factory.

The 1/2 can be tuned, has a tuning chart, and can be tuned.

That is not to say however, that the HW GM can't be setup without tuning.

The manuals are very clear, but they require a good reading with understanding...plus they show pictures.
 
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