The SL55 mains-only Satellite receiver, featuring the same sockets as the Porty, but with a 'lock' led to indicate a valid signal.
The Porty with a 12v option. It uses the same handset as the SL55.
The main failing with the original Porty was the poor quality of electrolytics used in the PSU section. With these capacitors upgraded to higher temperature versions reliability is excellent. Handsets are no longer manufactured and the factory charges heavily for anyone ordering one. I am told that later SKY remotes have the codes in , but I have not checked that out. Also some of the cheaper dvd player remotes share codes and can be used for some functions.
If using a preamp the 14/18v from the F socket is useful, however a 23cm yagi is a short-circuit at dc! You can do the mod shown at www.g8ajn.tv/comtech.htm
You may need to repair the track (seen here as a white link). To disable the dc to lnb, cut the centre leg of the regulator, or make a dc block aerial lead using a 25pF capacitor in series.
A switch could be inserted if the option is required. N.b. the heatsink is not grounded. Any error messages about a lnb short can be ignored.
The repeater output gives two audio channels, the left channel is the main one and the right channel carries the 2metre talkback channel.This enables those out of range of the repeater to still follow the dialog. Here is a simple way to combine the two outputs allowing you to adjust the levels to suit.
IMPORTANT! Diode D1 connects to the left pin of the LED and the capacitor connects to the right-hand pin of the LED viewed from the rear of the front panel. If using an electrolytic capacitor connect the positive side to the lock light LED. The circuit will not function if wrongly connected . Too large a value of capacitor may cause 'pumping'. Paul G6MNJ reports adding a 4.7uF capacitor to gnd from the junction of R2,R3 to prevent relay 'chattering' due to the 80% square wave signal used to drive the LED causing a ripple on the output of Q1. It might be possible to use a lower value (such as 0.1uF) on the gate to ground instead, but I have not tried this yet.
In the above photo you can see the red wire coming from the 5v supply line at D108 or the nearby pad for R71 (not fitted). See top inset.
The yellow wire takes the output from Q2 to the cut leg of the SPDIF phono socket for ease of connection. Ground was a convenient solder tag on the main board.
With no signal received set R1 to ground end then gradually increase until the output of Q2 goes high (about 4v) then take the pot back until the output of Q2 drops to a low voltage (<0.6v) . If you require an inverted voltage level there is sufficient swing at Q1 but a series resistor(>10k) will be needed to reduce the loading .
Monitor the output of Q2 and connect to a digital signal. When the lock light comes on the output should go high. Adjust R1 if neccesary to give consistent results.
If there is any likelyhood of the line being shorted out externally, a 100 ohm resistor could be fitted in line with the phono socket.
If the LNB volts are not required for a preamp it might be best to remove the dc supply rather than relying on the software to switch it off. Cut the long leg on the 2Watt 1.2ohm resistor R317 stood near the card reader board header as shown in the picture (left).