Posts by G4EML

    As previously commented the lack of the inductor is probably not important.

    Some time ago I modified one of the “8W” amplifiers so that I could test each amplifier chip on its own. Connecting directly to each chips input and output, bypassing the input and output combining circuitry and essentially testing as shown in the data sheet. The results for gain and output power for each chip were very close to the data sheet figures. So I came to the conclusion that the poor performance was down to the input and output combining circuitry and rf switching. I didn’t investigate any further as I no longer needed to use the amplifier.

    A UK Ham recently did a bulk buy of about 25 units from UIY. Circulators with 30dB 100W attenuators on third port.


    Final price per unit after postage and taxes was approx 25 UK Pounds each (28 Euros)


    Before you ask, no there are none left as far as I know.

    Yes, if the buffer fills up it is a sign that you are trying to send more data than the current settings can handle. You either need to reduce the amount of data you are feeding in or increase the rate you are sending out.

    The FEC setting adjusts how much of the available bandwidth is used for the video and how much is used for error correction. At a setting of 3/4 three quarters of the available bandwidth is used for video and the remaining one quarter for error correction.

    The best setting for FEC depends on how strong your signal is. If you have a strong signal you need less error correction so you can increase the value and get better quality video. If you have a weak signal you will have to reduce the value to give more error correction so that people can receive you, but your video quality will also go down.

    The best combination of video resolution, bitrate and FEC is a matter of experimenting.

    The GPS reference frequency is accurate but has small variations (jitter) which are then averaged out by the following PLL synthesiser to give the final output frequencies. This works well when the jitter has a high enough frequency. I suspect what is happening is that some GPS reference frequencies have a very low jitter frequency which the PLL cannot average out. By changing the reference frequency slightly you are probably increasing the frequency of the jitter, thus allowing the PLL to work correctly.


    The behaviour may well differ between individual units as the jitter will be dependent on the GPS receivers internal oscillator calibration.

    The location of the cut is not critical. Position A would make the most sense as it gives you more to make the connection with.


    The large diameter part is the feed horn which is designed to have a radiation pattern which will illuminate the dish. In a dual band feed this needs to be replaced by a plastic dielectric lens (removed from a ‘rocket’ LNB ) which does the same thing.

    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.

    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.