It’s been a quite long that I’ve built my experimental system and was heavily using it in the field. While general usage is OK, I faced an interesting problem – tuner oversensitivity.
The StarTrack SR-55X receiver I currently use, has a minor disadvantage – it’s indicator of signal quality is hooked AFTER the AGC circuitry, not BEFORE. What this means in general? This means that, when fine tuning the dish, signal quality will jump from 40-45% to 75-80% quite quickly, and stay there, regardles how you adjust the dish or LNB. So, receiver indication may change by 1-2%, but in reality, due to missalignment, you probably loose signal in the bad weather.
I’ve started researching market of available receivers, to find one with most linear indicator scale, a lot of time was spent on practical testing. So far, the best one for such tasks seems to be Dreambox DM500. Despite signal Q, it also shows SNR, and most importantly – BER.
Using dreambox is also great in aspects of schematic simplicity. Since it uses single 12V supply, we no longer need complex step-up circuitry, as in case with StarTrack SR55X.
So, my current test rig looks as follows:
1. A 7 inch car LCD monitor
2. Dreambox DM500 (of course clone one, since we don’t care about sharing, emus and so on, this one will also work)
3. Two items of rechargeable video camera li-ion batteries (Sony NP-F960 clones, 7.4V/6ah)
These batteries are hooked in sequence, so total output voltage is around 14.2V under full load and about 16V without load.
That voltage 14.2V looks a bit dangerous for me, so I’ve hooked 2.2 Ohm resistor in series with dreambox (LCD monitor powered directly). So far, system works fine. If this set-up will be handy and accurate in terms of antenna alignment, I’ll try to incorporate everything into single casing.