I saw videos where they are modifying these old meters to add peak detection. Battery powered, op-amp. What these remotes sites are that people keep talking about. They must have simple modulation, able to break into the transmission line (shutting down the station), no need for precision or accuracy. Anytime I see them, they are on a desk with three or more attached in series with them. 
Back when I used to frequent "remote sites", Birds were often left in line in the various Comms sites, (which weren't a big part of my concern for that period) as part of the installation.
Such devices were very much rarer in TV installations, where it was more common to rely on the power meters on the Tx.
Birds were good for a "quick check" by the "first in " maintenance people, who were supposed to be "jacks of all trades".
Techs called out to a proper fault, or on annual or so, "spec checks" would commonly use more sophisticated devices, probably lugging
a Spectrum Analyser along, with perhaps a HP power meter, or, as we did, a HP410C, Model 1I036A AC Probe, a Model 1I042A Probe "T" Connector, & a known accurate test load.
The advantage of the 410C setup for TV checks was that the "peak & hold" detector in the probe had a time constant quite a bit longer than a TV line interval, so the displayed reading was to a very close approximation, the peak voltage at sync tips.
The "spec" was for the Sound carrier to be 10 dB lower in amplitude than the Vision carrier, "sync tip power".
Take the readings with just Vision Carrier, note it down, then just Sound Carrier, note it down, calculate (HP10C calculator), & there you were!
Yes, we could have used the Spec An, & did so for "quick checks", but the 410C method was simple, repeatable, & had good accuracy.
Of course, that was in the days when Engineering companies were run by Engineers, not "Pencil Necked Beancounters", so your 410C had an up to date calibration!