SR-3602mini conversion notes

    Perhaps I should write down my recent experiences modify-ing SR-3602mini LNB's.


    The SR3602 comes in various versions; my earlier description was using the "SR3602 ACE" version, where modification was relatively easy because only a top lid had to be removed and the PCB (including the ESD-sensitive input ports) remained protected during the upgrade.

    These SR3602-ACE are very sensitive, have a lot, a lot of conversion gain and if I can find some more, I would buy them; I gave away my spares to allow someone else to get on the bird.


    What aliexpress now seems to offer is the "SR3602-mini" which is a different beast. You have to watch closely to see the difference; typically the different type is on the box in the picture.


    Mechanically the mini is very different. Hans PE1CKK has described how to modify them: http://www.hybridpretender.nl/25MHz%20reference.pdf. Please check the pictures there.


    The mini gives a few new challenges.

    Electrically it is similar to the other SR3602; 3567-chip, 25 MHz xtal (not value-stamped on my units), and the usual trick with the 6V stabilizers, the combination diode and the voltage divider to divide H-pol, V-pol, or port-off.

    Mechanically the unit is very different however.

    First, the F-connectors are attached to the lid but soldered to the PCB. You must remove the plastic putty and then un-solder the F-connectors to remove the lid, which is awkward.

    Second, the components are on the "bottom side" of the PCB, accessing that makes the vulnerable RF input probes accessible because if you left the PCB to access the components, you lift the probes which are now ESD-unprotected. The LNB I modified is now a lot less sensitive and I think I ESD-damaged it during my experiments. I don't know if my modification causes the impact or me causing ESD damage but it is something to note.


    Modification is very similar to earlier PE1CMO-recipes: replace stabilizer with parallel resonator (150nH, 270pF), remove xtal, remove capacitor xtal to gnd, add series resonator (another 150nH, 270pF, now in series) between F-connector and xtal input (see PE1CKK for port to use), and adjust voltage divider to make polarisation work again as described earlier. Also, remove capacitor at input of stabilizer or you will short the 25MHz reference carrier.


    I do find the mini less sensitive than the ACE version (tried a new one, for which I had not voided the warranty yet) but I don't know if that applies to all 3602-mini LNB's. Experiences?


    I also note that many aliexpress sellers now push the SR220 instead of the 3602 but few pictures of the innards exist. Has anybody tried those?


    I might try some more, once the shack temperatures has fallen a bit so that my solder doesn't spontaniously melt,


    Geert Jan

    Around a fortnight before the NB-tpx was released I published my SR-3602 mods, see here. However, since then I saw around 5 - 6 different hardware versions of this (cheap & fine working!) LNB. Modified all of them...


    What version did 'you' receive(d) (generally speaking) ? What the heck, there is always a solution to mod it and ... well... it costs a few dollars. So, if you screw up don't feel a centamateur*


    * In Dutch the word 'HAM' is 'zendamateur' , 'zend' is (almost) pronounced as 'cent' <-- being 0.01 Euro ... describing the attitude of the average HAM as being "penny wise pound foolish"

    I ordered 2 STAR COM SR-3602 mini via ali and the sender comeback that he will send me 2 Red STAR SR-3602 instead as the other are out of stock but the should be the "same". When I get them I open one of them and saw that the xtal had no value printed on and that it is a "normal" one and no SMD.

    I just tried it like Hans PE1CKK described it. Put all together and feed 25MHz from my GPSDO and it works fine. Tried it last weekend at a POTY Antenna and was happy, results was better than expected.

    I also modified a Starcom SR-3602 wihch was different from all others seen here (only a "nomal" Xtal on the "Backside" of the board).

    I bought and modified it, because the "neck" (after cutting away the "horn") measures 20mm and should fit inside the POTYs cavity.

    I will test this and the resulting performalnce in the next days.

    I already tested a VENTON LNB connected with an olive-clamp to the POTY - the result was very disapointing - tranpondernoise just 2dB with 1,2m offset dish.

    In the moment I have a Megasat DIAVOLO where I drilled a 22mm hole in the platic cap and just fitted it tight on the POTY (ca. 5.5 dB transpondernoise - this is very close to a LNB mounted exactly in the feed point without the POTY).


    Both tests were made with the "original" dielectric lens of the poty.


    I will report my result with the SR 3602 fitted inside the POTY


    73 de Johannes