Posts by G3WDG

  • 3cm Kuhne transverter

    I am seeing the NB transponder here quite clearly with a HB 10368/144 transverter tuned to 10368. Ahead of this is a 26dB gain preamp to help overcome the degraded performance of the downconverter at 10488. Some plots posted on the


    ES2HAIL BEACON IS ALIVE

    thread.


    73


    Charlie

  • WB TRANSPONDER TESTS

    Plots below show receiver spectrum with dish not pointed at the satellite to show reference noise level, and dish pointed at the satellite. Both NB and WB transponders visible. Dish is 3m, feed position possibly not optimised, and DU4BC preamp. HB downconverter. Polarisation is midway between V and H. WB transponder about 10dB above noise floor. Edges of spectrum have some intrinsic slope owing to SDR/software.





  • NB passband monitoring

    Transponder noise also here this morning. No signals seen in the passband. At the moment this is a conventional pipe cap filter based downconverter with 10224 LO. Image filter is tuned to 10368. DU3BC preamp at the feed. Dish is 3m. I will put the proper downconverter on shortly.



  • Es'hail-2 beacon frequency (non-amateur)

    Based on recent data from 10GHz EME experiments with the moon at low elevations at one end of the path, there should be little or no degradation at 10 degrees elevation for most of the time. This data applies to a 1.13m dish at the receiving end - smaller dishes will suffer additional ground noise at higher elevations than larger dishes, but at 10 degrees there will still be little additional ground noise. More info on these tests is in Dubus 4/18 p 118.


    73


    Charlie



  • Smallest Dish Size


    One possible reason for the lower than expected signal with your smaller dish may be a higher than expected background noise from transponders on nearby satellites. Probably not worth making too many conclusions yet - best wait for 'our' transponder and see how that pans out.





    73





    Charlie

  • Smallest Dish Size

  • Smallest Dish Size

  • What TX amplifier do you plan to use?

    Hi Achim


    Yes, the comments applied to depletion mode devices like power GaAs FETs. With enhancement mode devices like LDMOS it is different, in that drain current is zero with gate at 0V, and increases as the gate goes more positive. Very commonly people switch the gate voltage from zero to its operating value to perform T/R switching.


    Glad to be here and lots of interesting discussions going on!


    73


    Charlie

  • What TX amplifier do you plan to use?

    Here's a photo of the PA.


    Yes, it is always best to apply gate voltage before drain on any GaAs FET PA. Procedure is to start with about -5V on the gate before applying drain voltage, then carefully take the gate less negative until the correct value of quiescent drain current is applied. This only has to be done once when setting up. Normal operation would have that gate voltage present all the time (ie on receive as well as transmit) and then just switch the drain voltage on for TX. Good designs of power supplies include an interlock so that should gate voltage fail drain voltage cannot be applied.


    73


    Charlie

  • What TX amplifier do you plan to use?

    Quote from pe1chl

    AO40 was 13cm downlink, not uplink.

    Not exactly correct as I remember it.


    AO-40 also had a 2.4GHz receiver that was used a few times. I believe it was connected to the 24GHz downlink for the tests. I am using the same helix now as part of my dual band feed. At that time, I used a HB PA with FLL120 GaAs FET for the uplink, which is still working with about 5W output.


    73


    Charlie G3WDG

  • LNB De-sensing Question

    I guess we'll get a lot of experience with this once the transponder comes on.


    It should not be too hard to develop a filter (eg low pass or tuned notches) that can deal with such harmonics, if they turn out to be a problem.


    73


    Charlie

  • LNB De-sensing Question

    Hi Rolf and Peter


    Thanks for your observations. I was wondering mainly how immune the downconverters are to a strong local field from the transmitting antenna, particularly in the case of dual band feeds where the downconverter is physically very close to the TX antenna.


    As Peter has found there is very high attenuation of the 2.4GHz signal at the RF input to the LNB.


    73


    Charlie

  • LNB De-sensing Question

    From another thread, there has been a question raised about whether an LNB will suffer desensing or overload when the 2.4GHz uplink transmitter is active.


    2.4GHz should not propagate into the LNB input, as the waveguide is well below cutoff at 2.4GHz, although evanescent coupling may be possible? What may be of greater concern is whether there may be leakage into the high gain IF stages in the LNB.


    I wonder if anyone has tried this yet (while not pointing the dish anywhere near to the satellite!).


    73


    Charlie

  • Es'hail-2 beacon frequency (non-amateur)

    According to the literature, the phase centre of a helix is located very close to the reflector plate of the helix, so having the downconverter looking through a hole in the reflector plate should be OK.


    The helix will cause some blockage on receive, but probably not enough to cause a problem. I have a similar feed with 2.25 turns for a prime focus dish and it seems to be working fine on receive.