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RE: [linrad] Hardware Help Needed!
> I would like to use the Time Machine to explore the spectrum (with
> Linrad of course) above 14 MHz. But I have slightly modified the Time
> Machine so that the LO is a PTS synthesizer rather than a crystal and
> the ICS501. I did this primarily so I would have better frequency
> agility than if the Time Machine were crystal controlled, as is
> standard. Things seem to work better if I avoid feeding the PTS into
> the ICS501, and instead feed it directly into the 16V8B.
> To use the PTS in this way I have needed a circuit that squares the PTS
> sine wave into a square wave that the Time Machine can use. The circuit
> I am using is from DJ8ES and uses a BC849C to a 74ls00 to a 74ls90 (the
> circuit was in VHF Communications 4/00, and was meant for use with a 10
> MHz oscillator). Its performance drops off above 14 * 4 = 56 MHz, so I
> cannot use it to listen to the bands above 20 meters.
The 16V8B probably just needs enough amplitude and a signal that swings
around 2.5 volts. Try a fast transistor (BFR92 or similar) with
grounded emitter. 220 ohms from collector to +5V and a 10 kiloohm
resistor from collector to base. Feed with a capacitor to the base.
Plase near the 16V8B because you would need a 200 ohm transmission line to
not loose the signal in the RC filter 220 ohms would make together with
the capacitance of too much 50 ohm cable.
> I am thinking of using a simple wave squarer circuit from page 7 of the
> July/Aug 2002 QEX that just uses a BFR92 and 2 gates from a 7400, but
> with substituting ASL or F logic for the HC logic specified to improve
> the high frequency performance. But I suspect someone on the list may
> have a better suggestion.
The lower resistor values are to get a higher maximum frequency.
I see no reason to add the logic gates. The 5V output of the BFR92
should be perfectly ok for the 16V8B.
> I would like to get at least to 10 meters. That would require 30 * 4 =
> 120 MHz performance of the pulse squarer.
Should be no problem.
> EVEN BETTER would be if someone had a multiplier and squarer circuit
> idea, so that I could then with a PTS 500 run a direct conversion
> receiver on 144 MHz with the Time Machine. This would require an output
> at 144 * 4 MHz = 576 MHz. Input could be 144 MHz sine wave if the
> circuit is quadrupler, or 288 MHz sine wave if the circuit is doubler.
> Output must again be square wave.
On 144MHz you can feed the PTS directly to the mixers through cables
that differ by 0.25 wl in length. I do not think the 16V8B is fast enough
to divide by four at 576MHz;-)
> Time Machine has indicated they are 'working' on an approach for 144 mHz
> themselves, but although this was discussed with them in mid July, and
> they have good plans in this area I have not heard anything lately, so I
> want to proceed on my own. What Bill Coleman N4ES said in July was:
It is difficult to get a reasonable performance with direct conversion
Leif / SM5BSZ