Dual Feed For Uplink / Downlink

  • Hello All,


    I have enclosed a few photos showing what I have been using over the last several days. Thanks to the many stations that made contact with me on the EsHail 2 Satellite.

    The system basically comprises of the following:-


    A 1 Metre dish,

    Uplink / Downlink feed : 2.4 GHz Helix , 10 GHz Dual mode horn. This is a combined unit.


    Power Amplifier, Home design: 2 Watts input 25 Watts Output, driven at approximately 8 Watts output for this application.


    10 GHz Home design LNA / Mixer/ I.F. - LO chain 8089.5 MHz driven by 10 MHz GPS Locked.


    432 to 2400 Transverter, 10 MHz GPS Locked.

    The prime driver was the Scottie Globemaster SDR at a 432 MHz Intermediate Frequency. ( Fitted with the ‘ Scottie Drift Zapper ‘ option providing LO Stability of 0.007 ppm ). (Please see my QRZ.com and Globemaster Groups I.O. for details if you are interested. ).


    I have included some photos.

    Regards

    Ed GM3SBC

  • Founding father of this feed is G0MJW and I assisted with finding the right feed point to let it produce CP. It is modelled in CST Studio and a MP4 movie of the simulations canbe seen here . Will try to find the picture of the dimensions.


    In the meanwhile you can look at these ones here or here or here or here or here : -)


    Edit: below the dimensions of the feed. Spacing between patch and reflector is 3mm. I have the feed point at X,Y = 8,28 and a cropped square reflector.

    2300 - 2500 MHz simulation done by G0MJW is below. It confirms the right position of the feed point is critical for CP, i.e. balloon perfectly circling around Z = 50 + j0 Ω ! :


  • I can confirm Mike G0MJWs design works very well and is a tidy solution. I have been using it on a 0.6m dish with 5W and getting good reports. Even when my amplifier had a fault and I was only producing 100mW people were still hearing me.

  • Do you guys cut the waveguide on LNB and extend it with copper/brass tube?

    Is the length critical..

    Is there any difference between inner diameter of extension and the real waveguide of the LNB? Or is this difference critical??


    I am pretty new on upper bands..sorry for simple questions..

  • ta2nc : In my case (SR-3602 LNB) I cut off the horn. The outer diameter of the LNB waveguide is 20mm so it fits perfectly into the antenna waveguide (copper pipe). See this picture. The length is not critical, but don't make the antenna waveguide too short, otherwise you may run into troubles mounting the feed with the LNB bracket.

  • The length of the tube is not critical. It is acting as waveguide which has a very low loss.

    The differences in the inner diameters will work OK. Ideally it should be a smooth transition but a small step will not introduce much loss.

  • ..and yet another one, a Coaxial cavity feed like the OM6AA feed. The 2.4 GHz part is fed with two probes which simplifies the feeding compared to OM6AA feed. I only need one 90 deg hybrid , Anaren XC2500-3. Less prefect symmetry is the price to pay.


    In the 10 GHz part I have vertikal and horizontal probes so I can easily switch between NB and WB transponder with a SMA-relay.

    My 10GHz RX setup is NOT based on an LNB - it is scratch built with SMD MMIC:s.



    The feed is designed by SM6FHZ and is of course a compromise and not as efficient as the EME-feeds.

    I use a 2.3 m dish, f/D = 0.31 , it is actually a1.8 m dish extended to 2.3 m.


    https://sdr-radio.groups.io/g/…/0/S_X_Dual_Band_Feed.pdf





    Any one else using something like this or OM6AA feed ?


    73 - Hannes - SM6PGP

  • there is nothing infront of the feed cavity/waveguide opening. The entire "RF-head" is under a rain cover and have some heating to keep it 10-15 deg above outdoor temperature just to avoid humidity.




    73 - Hannes - SM6PGP

  • Hello All ,

    On the idea of ON7WP Pedro I designed this dual feed. After a few mistakes I finally managed to get LHCP and after reporting RHCP. The two horizontal yagi's are on the Y/4 in front of the two verticals. The antenna is 80 cm offset. With a power of about 2 watts from a SG labs transverter, a 10 meter feeder at a transponder level of -72dB provided a signal level of -64db. So I have already done more than 20 QSO.

    73 Rumen LZ1JH