The G5IJ antenna


The RSGB has kindly supplied a copy of the the G5IJ article, in Adobe Acrobat (PDF) form, which appeared in the December 2003 edition of RadCom. My thanks to Steve Telenius-Lowe, G4JVG.

G5IJ Antenna Revisited (PDF).

Radio Society of Great Britain, RSGB

the torriod The RG-58, 50 Ohm feeder wound on the torroid, 12 turns. [GM0GNT]
close up A close up of the co-ax braid, soldered to the centre tap of the bifilar winding and of the co-ax inner soldered to the same point. [GM0GNT]
quick and dirty The quick and dirty way to rig the aerial. The twin flex jammed in a velux window and the torroid hanging in free space. [GM0GNT]

 

In the interests of self-experimentation, I have reproduced a "thread" from the GQRP-L Internet newsgroup. I sincerely hope that none of the corespondents objects to their correspondence being reproduced here.

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Has anyone tried making the G5IJ aerial featured in Decembers RadCom?

The reason why I ask is I was unable to wind 1.3m of 50 Ohm co-ax through the toroid. Seems to work with what I managed to wind onto the toroid.

I've got some RG178 I may try and wind onto the toroid, should be OK for QRP operation.....

Wallace Shackleton, GM0GNT

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Hi Wallace,
glad the article has sparked more interest. You should get some responses as several of those who sent me information are QRPers.

73, Steve, G0FUW

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Walace asked:

>> The reason why I ask is I was unable to wind 1.3m of 50 Ohm co-ax through the >> toroid. Seems to work with what I managed to wind onto the toroid.

The diagram isn't especially helpful: I tried with RG58, but there's no way
I can get 1.3m on it without using the full diameter of the T200.

>> I've got some RG178 I may try and wind onto the toroid, should be OK for QRP >> operation.....

RG174 would seem to be OK, but it still doesn't look anything like the diagram: a photo may be more helpful. I get the distinct impression that this is a "suck it and see" type of project. But I too would like any tips that are going...

145, Pete PH1PH - G7ECN GQRP 2543 &c &c &c

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Hello Wallace,

>>Has anyone tried making the G5IJ aerial featured in Decembers RadCom?

Yes, I have.

>>The reason why I ask is I was unable to wind 1.3m of 50 Ohm co-ax through the >>toroid. Seems to work with what I managed to wind onto the toroid.
>>
>>I've got some RG178 I may try and wind onto the toroid, should be OK for QRP >>operation.....

I have used the smaller RG174 instead of the RG50 on a toroid T-130-2. So I don't want an additional error source I used the small coax also as coax to the transceiver without any cuts or solder points. The RG174 works fine with QRP.

72/73 de Ingo, DK3RED Don't forget: the fun is the power!

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Not 13m but 13 turns that will make it a lot easier

If you have any problems please do not hesitate getting in touch I have been using these things since 1996 almost exclusively in various locations

Roy G0TAK 2E1RAF

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There seems to be a little discussion on the G5IJ and a little bit of confusion.
May I recommend to you the original article from TT in Radcom March 1996 the length of Coax at 1.3m is meant to be the winding AND the feeder from the rig to the toroid.If you get about 13 turns on the toroid you will be about right.

Actually the length of the coax feeder is not critical, it was just the length that G5IJ found he needed.
If there are any further queries I will be happy to help, I have built about 30 of these as demo's and for farming out to friends so I have a little practical experience. I have been using them as a main station ant since 1996 and had a fair degree of success.
Not THE greatest ant in the world but it does work.
Roy G0TAK/2E1RAF

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Hello Julian,


>>I hope the feeder length is very short or most of your power will go in feeder losses >>unless the SWR of this antenna is much less than 3:1.


Yes, it was. I used the "necessary" length from the transceiver to the feed point and don't measured the length before winding. But I think it was only 2 or 3 metres coax.

72/73 de Ingo, DK3RED Don't forget: the fun is the power!

Roy, that information makes me feel better as I managed 11 turns onto the coil.
The only things I need to do are: mount the toroid in a weatherproof box to get the aerial out to the back of the house and extend the length of the "ladder line," I used the longest length of two-core flex I could lay my hands on. The insulation on the piece I was intending to use started breaking when it was flexed. All good things must come to an end..

I managed to get 9 turns (as shown on the diagram, assuming it's correct) of RG58 on to the toroid - fiddly, but possible. I didn't measure out the length (but surely it's the turns ratio that's important?).

I'm quite pleased with the results - I intended it mainly as an experiment and an independent general coverage RX antenna, but I've tried it on TX with the balun directly at the TX and no tuner. The antenna is 20m of 300 ohm ribbon shorted at the far end and about 25ft high. The VSWR ranges between 2:1 and 5:1 with the best SWR on
7, 14 & 18MHz and worst on 10MHz. I made quite a few 5W SSB contacts, including 1 in the US, on 20m with not unreasonable reports. I deliberately didn't use a tuner as I wanted to see how it performed if I treated it as a broadband antenna - which should be
one of the payoffs for accepting some inevitable loss in the balun.

I think the absolute minimum length of coax feeder between the transmitter and the balun is essential as this is where I would expect the highest losses.

I'm sure a long wire antenna of the same dimensions properly tuned against earth would outperform the G5IJ, but I do think it's an innovative way of achieving quite a good broadband match over several bands.

I suppose the acid test would be to stick both ends of the ribbon feeder straight into the rig & make the same comparison!

All good clean fun though!

73 Ian G4FSU

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Has anyone tried this?
The G5IJ toroid, when wound, will act as a fairly good receiving ant - without ANY wire connected to the 'output' side!
I have not tried it as a transmitting ant in this mode didn't think it wise.
Roy

Despite having used a length (about 15 m) of flat multi-core twin electrical wire 300 Ohm feeder, my attempt at this aerial went well. If you want a catalogue of DX contacts using this aerial then forget it, I'm not that kind of radio amateur - I'm a QRPer, I'm grateful for any contact that I make! However in the first week or so that I used the G5IJ I have worked UA3, HA5, OK1 and HB9, also heard a very weak EA6.

I have since replaced the flat twin with a 20 m length of 300 Ohm open wire feeder, to see what effect it has. First impressions are, that there is no difference, though in saying that the aerial comes from my first floor shack down to a small tree (2m high) and then down to a wall to run parallel with the wall for 5m or so..... and it still works!

My plans are to coat the coil in polyurethane varnish and mount it in a weather proof box at the back of my house and run the 300 Ohm as high and as straight as I can get it.

I obtained the T200-2 torroid from my good friend Peter G7JAB at JAB Electronic Components for the same price as Sycom.