DIY Helix for 2.4 GHz uplink. Can I use 5mm copper tubing?

  • I've used 5mm (3/16" actually) outer diameter copper brake pipe for a 25 turn helix antenna and also a 5 turn feed for my 90 cm off-set dish. I had my first Es'hail 2 contact with the 25 turn helix but had to use a Spectrian amplifier too at about 30W. With the 90 cm dish I can run an SG Labs transverter on its own (probably only 1W) into about 9m of 3/8" Cellflex with about 2dB loss and get a reasonable signal off the satellite. The transverter SWR indicator is green but I've not got around to actually measuring the match.


  • G4SDG thanks for posting nice picture. Is that a metal bar inside your 25t helix?


    I know that in theory you can have metal inside a helix according to some sources, but are you sure this isn't affecting the efficiency of your antenna?



  • OK sure this makes it less mechanically complicated, but wouldn't the 2,4Ghz TX efficiency be affected by that metal bar inside?


    0dbW (1W) into 26dB gain (dish) will give 26dBW out (I assume feed gain is already included in the dish gain .. this may be incorrect).


    14dbW (30W) into 18dB gain (25t helix) will give 32dBW out. (More than you should need to have equal signal level on the sat it appears)


    The gain difference between the two antenna gains should be 26dB - 18dB = 8dB.

    If true, that would mean you would only need 8dB more power on the helix to have the same signal as with the dish using 1W. Not 40W.


    You would only need to go to approx 8W (this is 9dB for the ease of calculation so you wouldnt even need 8W) on the helix to have the same power reaching the RX in the sat as from the parabolic dish with 1W in?


    You should have been approx 6 dB stronger when using the Helix with 30W. If that is the case, then the helix seems to be affected in some way?


    Note: my calculations may be incorrect.

  • My 25 turn helix was based on this design (eg http://www.amsat.org/articles/g3ruh/117.html) and uses a square aluminium tube. I should have explained that the 5 turn feed is for single band only, in fact a reworking of my AO40 feed as the original helix had fallen of while “in storage” and I couldn't find suitably thick wire to make a new one. Originally the 15mm tube had been just to the rear to support the reflector and ended flush with it but in the reworked version I used a longer pipe to additionally support the helix. The pipe is not acting as a 10GHz feed.


    I suspect that the 5mm tube used for the helix might present too much blockage for a dual band feed and I'm making a patch feed instead with the 22mm feed for 10GHz and a dielectric window from a Rocket LNB.


    Thanks for the calculations. Once done I'll make some proper measurements of feeds and the 25 turn helix all using the same power level.

  • Hi All, other than WIMO, does anybody know a good source of quality 2.4 GHz Helix antennas with 16 or more turns for those who can’t put up a dish antenna?

  • DD0KP and HB9SKA thank you for responding to my query.


    DD0KP really looking for a helix with RHCP so no losses are incurred, not sure how easy it would be to reverse LHCP to RHCP never done it before, and I’ll have a look on Google see what that turns up.


    HB9SKA everything I am looking for and it looks the part but it comes at a premium price, I suppose quality cost money. I’ll just keep looking.

  • G0FYQ use helixcalc you find in in the internet. Then you can calculate your helix for RHCP and print out a paper you put arround the pipe and then you know how to put the turns on the pipe.. very easy...:thumbup:

  • Mike,

    Have you looked at G3RUH,s Helix, I built one for AO40 which I still have.It is very simple to make, only requiring some basic hand tools. I'll Dig mine out ant post a pix of it here. The central support is a square aluminum section with an aluminum reflector cropped at the corners. The Helix uses 14 SWG copper wire( from an electrical shop): the supports are small teflon pillars. The matching section is a quarter turn flat copper , made from quarter inch copper pipe hammered flat and soldered to the first section of the Helix right at the connector nipple (N type).

    I may still have some diagrams which I could copy and try and get them to you. Hope this helps

    G8AWB

  • DD0KP thanks for that, not seen helixcalc before however I have been looking at these online helix calculators.

    G8AWB I would be interested also in seeing your build photos and design information, I have been looking at many helix websites / YouTube videos (http://ve2zaz.net/13cmHelx/13cmHelx.htm & https://www.qsl.net/oh4jzj/13cmhelixframe.htm) and the bit that’s not clear to me is this Impedance transformer which is putting me off from building one, so any clear information / photos would be much appreciated.

  • G0FyQ Apologies for the delay, I had problems upload the pix yesterday. hopefully they will upload this evening. pix 3112 gives the design details. 3108 shows the quarter wave matching section. This is a section of quarter inch copper tubing with one end flattened and a hole drilled to fit over the N connector nipple. the inside is soldered, as is the first quarter turn of the helix which is then placed inside the the tubing and soldered. Adjustment for best return loss is by adjusting the spacing between the matching section and the back plane. It takes longer to write about it that the time to do the adjustment. The Helical is mounted on a section of half inch square aluminum tubing. the stand off's are teflon although other materials should suffice. I hope this is of assistance.

    G8AWB

  • G8AWB thanks for the information posted it’s much appreciated, does the square aluminium boom impede the antenna in anyway because some designs I’ve seen don’t use that method?


    Also, does your antenna Impedance transformer look like these by G3RUH?







    Another interesting design:


    @DH2VA Another helix feed. Design by DJ4ZC, CAD and construction by DH2VA and final alignment by DL5MLO. If enough people believe, that the construction is compatible with hamradio, we could do another journal article..



  • Question still open: are people still interested in such an article? Lots of DIY involved. nothing from shops except screws and N-connector.

    Return loss measured and exceeding 25dB (which is VSWR<1.12).