Posts by om0aao

    G8UGD Thanks Adrian, but the surprise is that, I got better resulst with a wider bandwidth. Achim DH2VA has probably right that it depends how Simon calculates noise.

    I have tried:

    • 250 kHz bad results
    • 1MHz good results
    • 1,5MHz the same as 1MHz
    • 2MHz the same as 1MHz

    I have not tried 500 kHz yet.

    It's good to know for somebody that the reception with SDR could vary with the bandwith differently that in analog world. Thanks!


    did anybody notice that the bandwidth of SDR radio noticably change sensitivity and SNR? I am using SDR Console with a newgen RTL2832 dongle with standard setting of bandwidth 1 MHz. If I set 250 kHz, the gain, sensitivity and SNR change. Why?

    I have tried to make a circular feed based on the idea of DC2TH with a 2x 4el. PCB yagis from LZ5HP. I found that one yagi gives me good result so I decided to try this feed. Used 100cm offset dish.

    I make similar construction like this one:

    But I have make a small experiement with 1 yagi only. If the yagi was horizontal (above or bellow LNB), the signal was noticable stronger than I try vertical (left or right). The difference was abt. 4dB.

    Question - it is due that the feed is not absolutely in the focus point or due that the offset dish push the energy not consequent?

    Did anybody observe similar results?

    What do You think about writing QRZ + QRG in the forum? Of course, EL2DT similiar DXCC are quite interesting for anybody. But in past SAT HAMs were making an experiments - building stations, antennas, accessories, trying to excess distance records going portable etc.. It was good for someone who is interested in science and Eart-something-Earth communication but does not have a room for solid EME antennas.

    DX hunting was something mostly dedicated to HF with all behaviors of operation.

    I wonder is somebody can run on the transponder with homebrew setup, developing software, make realy QRP contacts etc. But that's my opinion. What's Yours?

    OUT: 21W

    IN: 2W


    Hi Sandro,

    Is that right, please? What's the Idq please? If I know, it is needed around 0,3 to 0,5A idq at least. So there is max. 0,6A of active current as photo shows.

    24V x 0,6A x 50% eff. = 7,2W out

    I am running 28V with Idq 0,5A. The output is modified by idea DK5DN

    and input is my idea - make PCB line (add wire and solder) thick as I can. I am reaching 28V/2,2A in key down. There is 2W input (or less!) from LZ5HP transverter. I dont know the output. No power meter SRI.

    Unfortunately the dish was damaged in transport. But Santa (in June, hi) brings me a present - D6 analyser. Not calibrated yet, but it helps me a lot.

    There are 2 screens, one is before aligment, second after. It was tuned toho high.

    Did anybody try to Fred deep dish with a moxon? Or 2 moxons phased fór circular polarisation?

    PA1EW Hi Ed, thanks for suggestions! You have rights, the N-connector body stands off the reflector a little bit. Good point!

    It is small picture - the black material is 3mm drill used for correct spacing. There is nothing, the plate is soldered and holded by the live pin of the N-connector.

    Probably this type of feed is not suitable for f/D 0.25, the parabolic dish effeciency is only 50% depending on the study:

    [Blocked Image:]

    Probably the dish was designed originaly to feed with a dipole and rod reflector spaced 0.24 lambda or so. There is teoretical effeciency more than 70%

    I rather changed my plans and order 100cm TV dish with higher f/D and will try helix. Think that it should work.


    @dk0kp Hello Heiner, yes, the screews can impact to the patchfeed but I don't think that they make -6dB.

    Studying materials about the feeds as SM6FHZ comparsion or W1GHz. It seems that with f/D 0.25 have patchfeed low effeciency. The most suitable f/D is 0.4.

    Hi folks,

    I have tried to improve my uplink with a 120cm dish. This is an old commercial dish with a low f/D 0.25.

    Now I am using linear polarised WiFi grid antenna PW 24 dBi,

    Due the low f/D I have choose K3TZ patch feed. I was calculating with a gain of 3dB for circular polarisation and 6dB for mechanical dimensions.

    Test shows only +3dB.

    I can confirm that th feed was placed correctly in focal point and SWR was not bad (indication on LZ5HP's XVRT), The reason why I did not reach the estimated gain is probably that the feed has not so wide radiation angle as I need for f/D 0.25.

    To imagine that 120cm dish has 30.8cm depth and focal point is 29.2cm from it depth.

    Has anybody an idea for circular feed for this parabolic dish, please let me know.

    Despite that I was living in very windy location I have choosen very stable setup for LEO satellites, 6el. DK7ZB (50 ohm) for 2m band and 10el.DK7ZB (28ohm) for 70cm band. Both antennas with vertical polarisation only. Separation between antennas was 120 cm.

    It was cheap solution with an actuator arm and works well. The elevation angle was around 5° to 70°. Why?

    Pointing higher than 0° decrease local QRM and noise. Only few passes are more than 70° and if yes, in moment 70° to 90° is the bird nearest so it is not needed to point directly on it. Second thing, the rotator was controlled by SAT software with ERC interface . In 30 second or less antennas were again pointed on it.

    On both bands were preamps used. Few times it was proved with winds above 120km/h and works well.

    Source SV1BSX

    But if You would like to buy a pro version, Alfa SPID is very good solution.

    I0LYL Nice work!

    I was thinking what choice will be better:

    1, XVRT near the antenna on the roof

    2, XVRT + PA in the shack

    Good idea and clean construction. CU in the burd!

    Thanks, Achim DH2VA ! But I am afraid that I am not very far from the real. I use signal strengh window which is showing maybe each second avg.signal strenght. First I tune on the beacon frequency, then few kHz away in free space.

    I have second LNB (uknown) so maybe I can try it with it. I think there can be difference, too.

    Thanks to everybody for a lot informations!

    I agree with g7iii that the WX can ruined signals. Both on downlink and uplink.

    Found that most stations use power 1 to 4 watts (30 to 36 dBm) and similar antennas but... the signals on the downlink varies more than 6 dB. That means some stations loose decibels somewhere.

    My question is if my station is working properly (NOT) and how weak signals I can receive.

    Now I can receive 1dB over the noise floor station with 24dB antenna and 25mW or 10dB antenna and 0,63W. As said G7iii - in ideal conditions.

    I will make more tests and try to make a small research... TNX!

    I am trying to calculate the pathloss and sensitivity of QO-100 transponder. Calculation:

    Au = 20 x ( - 4.622 - log f - log L)

    Au - pathloss in dB

    f - frequency in GHz

    L - distance in km

    My calclation shows that the pathloss is around -192 dB.

    My own carrier with 33dBm (2W) with 24dBi antenna is 20 dB over my noise floor. I am receiving with 80cm, LNB and SDR dongle. But I know that there are stations with better receiving conditions.

    My receiving floor:

    -192 dB + 33dBm + 24dBi + 20dB = -115dBm (0,4uV/50 ohm)

    But I don't know what's the gain of receiving antenna of QO-100. Did anybody knows that? And are my calculations right?

    What's Yours receiving floor?