Fun with filters and test gear

[N8YX]

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.

[AE1PT]

^^^^Do It!

That was one of the main purposes of the major test equipment upgrade I just finished (more or less...).

Old gear was great in its day. However there are many things that are known and available now that can make it even better. A good RF lab can take a real look at how filters and circuits function presently--and then give a look at the performance of design modifications. What Fun!

[N8YX]

I've now gone into pare-down/build-up mode. Much of the equipment I've collected over the years will get a final electrical checkup and/or cosmetic detailing then placed on the block.

Those 500/5000-series TM pieces are good, but I'm in need of a few higher-end pieces of test gear to supplement them. Namely: A spectrum analyzer, semiconductor curve tracer, higher-end logic analyzer and several other functions which the smaller stuff doesn't offer. As it is, I'm looking really hard at the 7000-series mainframe scopes and plugins for them. One is a 2.5GHz analyzer - and there is a curve tracer accessory.

Thus, time to recover some of my investment and roll it into lab-grade test gear.

I just scored somewhat of a rarity: That is, a Tek TS-4084. It's a special version of an AA-501 distortion analyzer which can perform SINAD rather than THD measurements. Was used by the military for comms-equipment servicing duties, and so will it be in my shack.

About those filters:

The Bulgarian Connection came through with enough rocks that I ought to be able to build 20 LSB and 10 USB versions, and I think I may be able to recoup a little money when all is said and done by selling these to the Mackay Group members.