My Dad put his Potomac FIM21 Field Intensity Meter on the bench.

In 1986, this radio cost $1,950—which is nearly $6,000 today! (And this isn't even the most expensive AM radio today—there's a newer version for $15,000!)

It measures the field intensity of AM radio signals in volts, and a calibrated unit like this one can be used for official readings sent to the FCC for broadcast stations in the US.

A few other things we mentioned in this video (some links are affiliate links):

Potomac FIM21 Field Intensity Meter: https://piusa.com/legacyproducts/
RTLSDR v4 dongle: https://amzn.to/3KvDbku
SaferCCTV AN200 Indoor AM Loop Antenna: https://amzn.to/3KvDdZE
Gqrx SDR software: https://www.gqrx.dk
We made a hot dog talk... with RF:    • We made a hot dog talk... with RF  
Workbench build video:    • Building the ULTIMATE Electronics Wor...  

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Contents:

00:00 Field Intensity Meter 21
01:13 Over 900!
02:22 How to take a measurement
03:14 Loop antennas, nulls, and SDR
05:56 External antenna testing
08:16 What about FM?
09:16 Why it costs thousands of dollars
10:46 Field Calibration
13:33 Is it still useful?
14:46 The importance of calibration
15:50 Justifying the cost... with a hot dog?