Best Results with a Serit FTS-4335 and MiniTioune v0.6d

[G8GKQ]

I've conducted a series of tests with the new Serit Tuner and MiniTioune v0.6d over the last few days and have the following recommendations for best results:

1. Make sure that the input of the Serit tuner is fed with a 50 ohm source impedance. The tuner phase noise increases below 500 MHz significantly if the input impedance is at all inductive. I used this circuit on the input, and in some situations it increased the best MER from 18 dB to 27 dB at 146 MHz 333 KS, and also increased the tuner's ability to lock on to signals in noise. The variable capacitor peaked for best MER at about 11 pF for 146.5 and 8 pF for 437; other tuners will probably vary.

Input network.JPG (12 KiB) Viewed 3510 times

2. Arrange your system so that the input level indicated on MiniTioune is around -50dBm at 333 KS. Note that the indicated input level (for the same actual power input) decreases by 6dB each time you double the SR. So if set for -50dBm at 333 KS, it will read -60dBm at 1000 KS for the same actual input power. You will need quite a lot of amplification between the aerial and the tuner - make sure that you put some band-pass filters in there too!

3. When starting MiniTioune, click the DVB-S button. If you leave it in Auto, the tuner will not acquire the signal until it is about 3dB stronger than with DVB-S selected. Once acquired, the setting makes no difference.

I compared the ability of the new tuner to lock onto signals in the noise (at 146.5 MHz) with my old SUP-2400/Sharp Tuner system, and the performance was identical. Well done Jean-Pierre and Brian!

Dave
G8GKQ

[g0mjw]

Dave,

Thanks for this post. I had managed to miss it. I don't really understand how this is working though because this is compensating for a miss-match. When I did my MER tests it was not a lack of signal so I think it might be more towards preventing reflections or oscillations or maybe something to do with the mixer.

The problem is in a multi-band situation, won't the parallel capacitor be a problem on 23/13cms?

Edit- I have done the impedance matching. The capacitor didn't work for me so I left it out. It may be the RPI source wasn't good enough but MER was above 20 and that's good enough.

Further Edit - it must be good enough, received G8GTZ from Walbury in 32 APSK 333ks/s on 146.5MHz

Mike

[G8XZD-TV]

Has anyone given some thought about the best way to switch filters/preamps etc ahead of the serit. Possibly one input for 2/70' the other 23/13?
Or do people think it would be best to keep filters/preamps external to the minitioune enclosure?

Been thinking about several scenarios, just can't make my mind up.

73. Ian.