u can change R5 and C3 to suit the type of input circuit you are driving. Th

Isolating the Porty/SL55 DC lnb feed when using a yagi or filter rather than a pre-amp.

Cutting the leg of the LM317 regulator does remove the dc at the rear socket, but generates an error message on screen. This mod avoids that happening and does not require the regulator leg to be cut. Later models can also be modified but components are often repositioned.




SL100HD        STARSAT

Most Free-To-Air DVS (satellite tv) receivers are useable provided they are capable of demodulating digital signal rates as low as 4 Ms/s. Terrestrial DVT and SKY boxes are not suitable for ATV.
If you are looking for a Repeater input receiver you will need to find one capable of giving a 'valid signal' detect line. The reason that you cannot simply use a sync detector is that there is a caption generated when the signal drops out and this generates syncs , meaning that it is impossible to differentiate between the signal and the caption.
The elderly SL55/56 has proved ideal. For use in a repeater the Porty has a few disadvantages especially when handling signals from modern encoders. Not surprisingly as it is a rather old model now. The NDS makes a good home receiver but as it is designed to be tuned to a fixed transponder in a rack mounted system it will need to be retuned to accept different signals, making it unsuitable for repeater use. The new BigSAT seems an excellent replacement for well under 40 but it appears to suffer from audio channel firmware errors that could be a problem for a repeater. Following considerable research there is now an option to use the Comag SL100 receiver by adding a small circuit to create a lock-light type signal.Details below.The Plaza has a built in lock light, we are currently assessing the receiver and will report here later.

The Comag Porty is a low cost Free-to-Air satellite receiver, the mains-only Porty and the mains or 12v SL55. Almost identical but the SL55 has a useful 'lock' light feature that enables a transistor to be added to control other equipment such as a repeater changeover or a recording device to be triggered. Remote controls are identical for both models but are in short supply. The same unit is often rebadged as Silvercrest and other names so most univeral remote controls have the codes in them. I have placed what information I do have (no circuits have ever been seen) on this page and a number of links that might be of interest to you. A copy of the instruction book is here.
Manual tuning of a repeater signal method (actually for GB3SQ reception but relevant for others) is here.


To prevent the on-screen message ' there is an lnb short-circuit' appearing when the dc line to the tuner and aerial socket is either open or short circuit, lift the collector(centre)lead of smd transistor QL3 (just in front of regulator heatsink) and cut the dc line to the tuner by slicing the track just above RT3 (SL55) or CT5 (Porty) with a knife. Dont worry about cutting the thin ground track alongside the edge of the board as it is not needed. (SL55 layout shown)

What to do if your receiver has no lock light

Receivers using the Sharp tuner can get a signal from the tuner itself that can be used to trigger other circuits.
Pin numbers may vary with different versions, on the early ones it was pin 1. Check with a voltmeter on an on/off signal. This will work on any incoming, either digital or analog signal.



Using a sync detector circuit such as the LM567 on the analog receiver to indicate a valid digital signal cannot be used here as the digital receivers display a 'No signal found' OSG which generates syncs internally and the detector circuit cannot distinguish between this and the received syncs. Thankfully the processor chip does have a detector circuit that is used to light up the front panel lock LED.

If you are using the SL55, which features a LOCK light, you can use the voltage across the LED to trigger the repeater (or recorder or whatever).
Using a digital switch FDV301N (or a NPN transistor) this circuit can trigger a TTL level or PIC chip input port, use a following stage to invert to positive on a valid signal if preffered.The Porty has a pick up point on the pcb near the processor chip that can be used, but the lock light is not fitted.The later version Porty 2 has a 'lock' solder pad near the tuner can.

Fitting a Lock Light on the BigSat Receiver. Designed by G8DRK
Big SAT Int.
Adding lock light switch output to the German Big Sat International receiver. The card reader should be unplugged and removed to allow space for mods board.

In the photo you can see the red wire coming from the 5v supply line at D108 or the nearby pad for R71 (not fitted).


TR1 base and emitter are connected across the Lock-LED, so TR1 can only turn on when the LED does. Therefore all invalid strobing pulses (the ones to light the channel display segments) are ignored. R1 just limits current into TR1 base so the LED is not visibly dimmed. On each valid pulse (the ones we're interested in) the strobing chip pulls the LED anode high (along with TR1 base) and, simultaneously, its cathode is pulled down to chassis - and with it, TR1 emitter. This allows TR1 to turn hard on, rapidly charging C1 to 5 volts.
This voltage across C1 enables R3 to feed current into TR2 base. TR2 now turns hard on, delivering a 5 volts "high" across the pull-down resistor R4. Between each strobe pulse, the voltage on C1 will fall a little, but not enough to prevent TR2 from remaining fully saturated. So no strobing pulses appear on its output, just a constant 5 volts. R5 limits the available current, preventing damage to TR2 or the 5-volt supply if the output lead is shorted.

When the LED goes out (stops pulsing), C1 is no longer being "topped up" via TR1. C1 discharges via R3 and TR2 base/emitter until, at around 0.7 volts, TR2 starts to turn off. R2 completes the discharge, sharpening the switch-off characteristic. With TR2 off, the output drops to 0 volts. The channel display is still lit so there will still be pulses appearing on TR1 base and its emitter, but if both are pulsed high together, both low together, or base low with emitter high, the transistor remains off. Only pulses intended for the Lock-LED (simultaneous base high and emitter low) will forward-bias TR1 and "wake the circuit up". In the photo the 47k resistor goes to the left-hand led pin .This board was supplied by Robin.


I use the output directly onto a serial to USB converter to trigger the FileStart program to begin streaming to the BATC site when a signal is received from the local repeater, GB3SQ on 1304 MHz












































































A blurred close-up of the connections.

At GB3SQ we tried using the BigSat. Its receiving performance was fine but we had a couple of issues that arose during use. Firstly the difficulty in remotely operating the menu to get to the bar graph signal report page,it is two levels down on the menu.

More seriously, we found that the audio left and right channels were swapping under certain conditions. Had they been strapped into mono it might not matter but as we require the left channel to be the main speech channel and the right channel (on the input side) is the DTMF control channel swapping L & R would clearly be a nuisance. Others have since reported having the same problem.If the bug was corrected in a firmware upgrade it would be an ideal unit.

At GB3SQ we use the FileStart program to provide streaming automatically when the repeater is in use.The receiver is at my home QTH connected to a PC that is on 24/7 anyway supplying live weather reports to this website. By using a serial to USB dongle it can be triggered from the lock light on the receiver.
As it can start more than one .exe file it can also create a useage log file, switch on a monitor or sound an alarm whenever the repeater comes on. Free download elsewhere on this site.

Ivor G1IXF and Viv G1IXE have found another receiver with a locklight , the Manhattan Plaza XT which has a 'signal' LED on the front panel. It means that the 1.8v used to light the 'signal' LED can be used to provide a dc output. Robin G8DRK has used the circuit shown to provide a dc swing of 0 to 4.5v.
Originally released in 2007 the Manhattan Plaza XT does still seem to be available at several UK stores. Prices range from 30 to 60.

As there are just a few components I decided to attach them to the rear of the front panel across the 'signal' LED. The view is from above the unclipped front panel so the LED is actually the lower of the three. The PNP transistor is soldered by its emitter leg (stump?) to the LEDs anode whilst the base goes via a 4k7 miniature resistor to the cathode pin. The orange wire goes to the output socket via a 1k resistor with another 1k taking the collector current to ground. Being more sensible than me you will probably not use use a surface mount transistor. Any general purpose pnp transistor should be fine. Robin advises that you do not directly connect the front panel chassis to any other chassis point on the case or main PCB as it can feed noise onto data lines and make the receiver's software unstable - intermittent loss of sound etc.
no menu? click here

SL100 LockLight Mod


To remove DC to the aerial socket on the StartSat receiver, cut track by the last letter T of the printed STARSAT name, to the right of Q3 in the photo. Use the G8DRK mods as for the BigSat etc.for connecting to the locklight.

By rectifying the digitally encoded video on Pin11 of U45 the fet switch Q1 discharges the 5v across C2. The gate of Q2 goes low forcing the drain voltage high at R4.
With no signal the digital stream stops and C2 charges through R2 turning Q2 on and removing the 5v at R4/R5.
You can change R5 and C3 to suit the type of input circuit you are driving. This works well into an LED and/or a PIC input port.

By rectifying the digitally encoded video on Pin11 of U45 the fet switch Q1 discharges the 5v across C2. The gate of Q2 goes low forcing the drain voltage high at R4.
With no signal the digital stream stops and C2 charges through R2 turning Q2 on and removing the 5v at R4/R5.
You can change R5 and C3 to suit the type of input circuit you are driving. This works well into an LED and/or a PIC input port.