Posts by G8AWB

    As a matter of interest I am using a DB6NT 10 Ghz down converter , with a DJ7GP dual band feed with a 60cm (2ft) prime focus dish which originally I used for AO-40 uplink. The received signal level is the same as an 80cm off set dish with a modified octagon LNB. The figures were by comparison using SDR console, so are not a rigid measurement or really scientific but gives an idea of the difference.

    Ray G8AWB :)

    Peter, I also have one of these dishes, again it was used for AO40, with A patch feed, both the one from James and a home brew version. This will be my link antenna for QO100 once Have the all the up link equipment completed. G8AWB

    I am interested in DJ7GP dual band feed, can anyone tell me the beamwith of the the two feeds. I understand the the feed is designed for a F/D =0.7. Is this correct?


    G0FYQ The square section boom does not affect the performance of the antennae at all. I have made a number of helical antenna using a aluminum boom without any problems. The one thing to be aware of is that you must not use strained wire for the helix: I did this on one of my helix antenna, and the results were very odd, the RF take off came at about 30 degrees from the axis of the boom. The quarter wave matching section is in fact the same as G3RUH's matching section but was easier to fabricate and mount. The antenna was tested at the AMSAT -UK test range with the following results

    Gain 14.8dbi
    Circularity 1 db

    Return Loss 19db


    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.



    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


    My plan is to use a Drake 2880 MMDS that I used for AO-40. This will be connected to a Directional Coupler via attenuators as not to overload the Drake. This will them be connected to a dongle, to give visual and audio indication, or to a receiver for just audio. The were a quite a number of these sold when AO40 was operating, along with a number of other MMDS converters. With this set up I will leave the coupler inline and will be able to monitor my signal continuously.