Click on one of the 4 main units in the picture for more information.
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This was originally designed by G8CMQ in 1984 but has many mods added to it since then, mostly suggested by Mike G8LES. Click here for an inside view of mine. I have recently fitted my own preamp but originally I had an 'LMW' preamp in the space at the left hand end. Now the antenna socket goes straight into a G8CMQ designed front end/mixer in the diecast box (with lid removed). The tunable IF is a Mullard ELC1043 TV tuner, which I have arranged to tune, at the antenna, 1240MHz to 1320MHz with a 270° turn of the Tune knob. The baseband IF output at 38MHz is demodulated by a PLL IC (NE564). This gives the added facility to give an apparent control of bandwidth. The sound demodulator also uses a PLL IC (NE564) and has a varactor tuned frequency range, set on a front panel control, of at least 5.5 to 6.0 MHZ. To save front panel space I used just one meter switched to indicate: subcarrier frequency setting / main tune frequency / signal strength.
I added a 'Buzz filter' circuit (click to see board) on a sub board which puts the video signal into the audio amplifier. This can be very useful for instance, when out portable, as it enables you to adjust beam heading by ear whilst out of view of the monitor. I also added a pcb circuit to give three independent video outputs eg. for: monitor, VCR & video to an ATV TX for relaying (say, on 13cms). Just recently (April 2003) I added a line sync detector circuit (click to see board) to provide audio squelch (to save damaged eardrums & loudspeaker when a local closes down!). It is similar to the various published designs using an NE567, such as: CQ-TV 200 p42, VHF Communications 2002 Q4 p232, Johannes DL4EBJ's design... and so on.
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