N8YX
11-24-2012, 02:01 PM
Finally got enough Tek TM500 pieces around here to do something useful, so I configured one of my mainframes thusly:
SC-502 scope, RG-501 Ramp Generator, DC-504 Frequency Counter, FG-502 Function Generator (with variable center frequency - which allows one to do something neat.)
The RG-501 feeds the FG-502's VCF In port, turning the unit into a sweep generator. It also feeds the Trig In port of the SC-502; when the scope's Sweep control is set to "Amp", the incoming ramp voltage sweeps the display.
The FG-502's output goes to both the DC-504 counter and to the filter under test. Filter output goes to CH1 input of the scope.
What we've done here is to make something akin to a spectrum analyzer, which will allow one to plot the response curve of a given crystal filter and visualize it on the scope.
One project I've been meaning to tend to is the creation of an LSB filter for my Mackay Marine 3030AR/30301A receivers. I have the USB filter out of one of them for reverse-engineering purposes. It uses a quartet of 2-pole monolithic crystal filters centered at 4.9987MHz, has tunable input/output coupling and cost over $600 as an accessory.
It also rings like mad.
Test rigged a lowly Yaesu XF-8.9 CW filter ($69.00 new; same era as the Mackay stuff) and its single "ring" is considerably removed from the fundamental peak - far enough away that the intrastage MCF will kill any residual leak-through. It's also ~40dB down from the fundamental.
I'm now tempted to build a replacement for the Mackay USB filter in addition to constructing the LSB unit.
SC-502 scope, RG-501 Ramp Generator, DC-504 Frequency Counter, FG-502 Function Generator (with variable center frequency - which allows one to do something neat.)
The RG-501 feeds the FG-502's VCF In port, turning the unit into a sweep generator. It also feeds the Trig In port of the SC-502; when the scope's Sweep control is set to "Amp", the incoming ramp voltage sweeps the display.
The FG-502's output goes to both the DC-504 counter and to the filter under test. Filter output goes to CH1 input of the scope.
What we've done here is to make something akin to a spectrum analyzer, which will allow one to plot the response curve of a given crystal filter and visualize it on the scope.
One project I've been meaning to tend to is the creation of an LSB filter for my Mackay Marine 3030AR/30301A receivers. I have the USB filter out of one of them for reverse-engineering purposes. It uses a quartet of 2-pole monolithic crystal filters centered at 4.9987MHz, has tunable input/output coupling and cost over $600 as an accessory.
It also rings like mad.
Test rigged a lowly Yaesu XF-8.9 CW filter ($69.00 new; same era as the Mackay stuff) and its single "ring" is considerably removed from the fundamental peak - far enough away that the intrastage MCF will kill any residual leak-through. It's also ~40dB down from the fundamental.
I'm now tempted to build a replacement for the Mackay USB filter in addition to constructing the LSB unit.