[Hallicrafters] TS-173/UR information request

[Mike Everette]

The TS-173 is a heterodyne frequency meter, derived from the BC-221 series but covering the VHF range starting at about 90 MHz and I think going up to either 300 or 500 MHz on harmonics.  It uses a calibration book similar to the BC-221's cal book, but has a 5 MHz crystal instead of a 1 MHz.

There are actually three more or less identical units in this family, each covering somewhat different frequency ranges (I'm not sure which is which): The TS-173, 174, and 175.  One of them is calibrated (in the cal book) up through 1000 MHz (yeah... right!).

By the way, if you don't have the calibration book for the instrument, read no further.  Without it, the unit will be useless.

The crystal in the 173 isn't a high precision type; it's basically a 5 MHz crystal in an FT-241 style holder, soldered into an octal base.  In the original application there is no provision for externally setting the crystal frequency against a standard such as WWV; you just took it on faith that the crystal frequency was accurate and that is NOT good enough by a long shot.  If the crystal isn't dead on 5 MHz it will have a very detrimental effect on the accuracy of the instrument.

I am about to suggest something radical, and perhaps downright anathema to you mil-radio purists... but if you intend to use this unit at all, you'll have to bite the bullet and do it.

Take the chassis out of the case and as carefully as you can, determine the location of the crystal trimmer capacitor -- a small air variable -- with respect to the top of the case.  Drill a hole in the case (AAAUUUUUGGGH!), mayve 3/8 inch diameter, directly (or as directly as you can) above the trimmer so you can stick a screwdriver down into the unit and adjust the trimmer.  You can get fancy and install a small funnel-like tubing guide to help your blade find the trimmer.  That will actually help a lot.

Keep that hole covered with a round snap-in metal plug unless you are setting the crystal.  Opening the hole will allow enough change in the internal temperature (escaping heat) to affect the master (variable) oscillator.  I know this from experience.

Let the unit warm up at least an hour before trying to use it.  Then, first, zero the cal crystal with WWV at 15 MHz, using the trimmer.  Then proceed to calibrate the master oscillator with the crystal, just like you would a BC-221; and use the instrument the same way.

DO NOT close-couple the instrument to a transmitter, because the strong signal from the transmitter will "pull" the master oscillator frequency to a noticeable degree.

The TS-173 is rather sensitive to air currents and changes in ambient temperature (remember the caution about the hole, above?).  Check the cal crystal against WWV OFTEN -- and EVERY time you recheck the master oscillator calibration, check the crystal first!  I found that it may be necessary to check the crystal every five or ten minutes if you intend to do any sort of serious work with the TS-173.  (Yes, I have one on my bench.)  But these things were mostly used for checking radar and IFF equipment, which emits rather broad signals; so pin-point accuracy wasn't really needed.

I did use mine to rough-align 2-meter FM receivers, a number of years back... they are stable enough to do it if you don't let the wind blow on them.  Just don't expect frequency accuracy tighter than five or ten KHz at best, on 2 meters.  I would not dare use one to net an FM transmitter on frequency in the commercial high VHF range, or even on 2 meters.  As for using the 173 higher than 2 meters... well, MAYBE up through 220 MHz but higher than that, forget it.  Unless you just want to get in the ball park.  But then you start worrying about exactly which harmonic you're listening to, etc.

I'm almost inclined to think the best use for a TS-173 is as a source of a metal case for a BC-221.  The cases are identical.

By the way, you can use a BC-221 or LM up through 6 meters, with very good frequency stability and accuracy.  I've used one to align and net FM receivers (the modulated LM or 221 has PLENTY of FM) and even set repeater transmitters (!!!) BUT I do the same thing to the 221 as with the TS-173 -- check the cal crystal against WWV, first.  I was able to get better than 200 Hz accuracy on 6 meters.  Amazing what you can do, when you haven't got a counter... in desperate times, desperate people do desperate things.

73

Mike
W4DSE