Posts by G4EML

    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.