UPLINK - PATCH VS HELIX - what's better

    Quote from DH5DAX

    May I call you Schrödinger's Ham? ;) You are right and wrong at the same time.

    ... nice :)


    but true. We need the confirmation by experimental ... you did it.


    Now the only problem left is that the stacking of 2 antennas means that the E-diagram is only half as high as the H-diagram, which leads to a non-ideal illumination of a round parabolic reflector, right?


    Btw, the the example with the 4 LNBs was a joke ... We know that the profit of a parabolic system comes from the reflector surface and not the gain of the Feeds ...


    73

    Robert

    • Official Post
    Quote from DH5DAX

    the same way you would mount sunglasses on your nose ;) the dimple is 40mm so it snugly fits over a standard lnb

    OK I see it, but you have to fix/mount the "sunglasses", otherwise it falls to ground. I mean the "eyeglasses frame".

    Quote from HB9SKA

    OK I see it, but you have to fix/mount the "sunglasses", otherwise it falls to ground. I mean the "eyeglasses frame".


    the fit is very snug on the octagon I used for experimenting, you have to force it on so it doesn't fall off even with some wind - I initially intended to make a 3d-printed adapter flange to fit around the lnb neck. that's what the three holes around the "nose dimple" were intended for. but as I already wrote, this was just one of my first dualband feed experiments which I have abandoned in favor of the G0MJW patch with waveguide feed. it is so convenient in many ways, the best I have tested so far.

    Hello OM´s

    today I will show here my 2,4GHz feed together with a Octagon LNB in a 80cm offset low cost TV dish.

    This are two 4el PCB yagis from LZ5HP, nom. 2320MHz. Was a present to my bulk order.

    Changed the elements to 2400MHz by cutting. Feeding is LHC over 90deg phase shift left antenna. Combined by two L/4 75ohm RG179 cables.


    Difference between feeding my 80cm TV offset dish with one yagi (vertical or horizontal) to the LHC combination there is a gain of near 3dB measured over signal at the satellite. Seems all right with RHC polarisation. Shure, pointing to dish is not perfect.


    Before I used two dipoles in front of a reflector plane, see last picture. Result was 1-2dB less, because over illumination of the dish.




    two dipoles LHC, very simple feed at my beginning, ok for qso's with 100mW.


    73,

    Wolfgang

    Edited once, last by DC2TH: PS: Today I have determined the degradation of the reception power by the transmitting antenna. It is less than 0.5dB. ().

    Like 12
    Quote from DC2TH

    Shure, pointing to dish is not perfect.

    Wolfgang, tnx for detailed report of your equipment!


    I would be interested to know how far the focus of 2.4 GHz and 10 GHz differs. That would be easy to test if you focus your 2.4GHz uplink and control the 10GHz downlink via web SDR.

    So we get a result: is there any measurable difference, and if so, how much is it ...


    73 de Robert

    I have now built the 2 phased helices above and below the Octagon LNB.

    With 10W at the feed and 85cm x 75 cm oval dish my CW test signal is about 1dB below the CW beacon so not too bad...

    The helix matching sections are currently airspaced and it is wet so could still be improved. The advantage of the helices is that they are wideband compared to patch feeds.

    • Official Post
    Quote from G4CDF

    I have now built the 2 phased helices above and below the Octagon LNB.

    With 10W at the feed and 85cm x 75 cm oval dish my CW test signal is about 1dB below the CW beacon so not too bad...

    The helix matching sections are currently airspaced and it is wet so could still be improved. The advantage of the helices is that they are wideband compared to patch feeds.

    Can you post any photos pls ?


    Tnx Thomas

    Here are some pictures.

    I have done some rough modelling using MMANA-GAL.

    From an optimum illumination perspective four helices would be better but more complex and this seems to be a good compromise for my oval dish.

    Note that the matching stubs are air spaced so susceptible to snow and ice. The central brass rods of the helices seem to have negligible effect on modeled performance.

    No effect on receiver performance, either feed blockage or RF interference has been noticed.


    Does anyone know where I can find expected received signal level relative to the beacons for a given EIRP? I need this to determine whether this antenna is really working as expected.


    Mike G4CDF

    Quote from PA1EW

    Nice idea!. To add some weather protection the following construction could be used. Possibly adapting the size of the PP-box as required.


    73 Ed PA1EW

    Ed,


    Did you detect any reduction of Rx or Tx signal because of the PP box. This is a very good idea: there are many different sizes of box available.


    73 Mike G4CDF

    Robert,


    When I tried this approach my main concern was the non ideal illumination even with my oval dish but I tried it anyway (see my previous posts). It seems to work quite well for me. The extra losses associated with combining 4 helix antennas seems to outweigh the advantage of better illumination and is mechanically difficult.


    73 Mike G4CDF

    Quote from G4CDF

    Ed,


    Did you detect any reduction of Rx or Tx signal because of the PP box. This is a very good idea: there are many different sizes of box available.


    73 Mike G4CDF

    I believe that every plastic box that has the microwave safe symbol is suitable for this purpose.

    Quote from G4CDF

    Ed,


    Did you detect any reduction of Rx or Tx signal because of the PP box. This is a very good idea: there are many different sizes of box available.


    73 Mike G4CDF

    Mike,

    The upside-down cheap food-box is made of Polypropylene PP5 and after being microwaved with >500W RF:) it stayed cool! (however, it has no microwave safe mark. This plastic is very sturdy, so sawing-drilling is easy. Only made RL-measurements with the "boxed" Helical feed in the feedpoint of a dish, measured abt 25dB at 2400MHz.

    Performance with my current 1.1m offset dish and abt. 3W at the Helix is very good, but could still be interesting to measure for any reduction on 2.4GHz and also for 10.5GHz using this type of weather-protection. I will come back on this.


    73 Ed PA1EW


    Update: I did test today using the PP5 plastic lid from the box. Placed in front of my LNB and checking the lower beacon I could not detect any signal reduction!. So 10.5GHz seems not bothered by polypropylene 5 plastic sheet, at least very little.

    An advantage of the upside-down box is that there is no condensation problem with the open underside.

    Hello OM's,

    thanks for all your helpfull informations.

    Can some call their relative levels to the beacon level with their antennas and transmit power at CW?

    Would be nice to have comparisons.

    Here with 1W and 2x 4-el LHC as feed arround the Octagon and 80cm TV dish today about 6db under the beacon.

    By test today with only one 4el. horiz. direkt to O-100 level was 20db below CW beacon.

    73,

    Wolfgang

    Quote from I0LYL

    I believe that every plastic box that has the microwave safe symbol is suitable for this purpose.

    Thanks Lucio, today I bought a cake box that is made from PP5 and is microwave safe. When I can I will test it on receive before I fit it.

    Unfortunately the power amplifier has died for some reason and I cannot transmit at present.


    Mike G4CDF

    Quote from PA1EW

    Mike,

    The upside-down cheap food-box is made of Polypropylene PP5 and after being microwaved with >500W RF:) it stayed cool! (however, it has no microwave safe mark. This plastic is very sturdy, so sawing-drilling is easy. Only made RL-measurements with the "boxed" Helical feed in the feedpoint of a dish, measured abt 25dB at 2400MHz.

    Performance with my current 1.1m offset dish and abt. 3W at the Helix is very good, but could still be interesting to measure for any reduction on 2.4GHz and also for 10.5GHz using this type of weather-protection. I will come back on this.


    73 Ed PA1EW

    Thanks for the information Ed.

    As reported above I have taken your advice and purchased a PP5 box and hopefully can test it soon.


    73 Mike G4CDF

    • Official Post

    its no so much a matter of asking but a matter of measuring. If properly done, you would have to do it at the feed. Unfortunately, this is 7/16 coax connector there and even then we would require the precise antenna gain.

    But as a guess, 3m is 35dBi and 100mW is 20dBm so we have 55 dBm EIRP, maybe 3dB more.

    A 90cm dish has some 24dBi, so 2W should be equivalent. Which I believe experience has already shown.