Radio dating accuracy
In the early thirties, National had grown from a company that produced radio parts and regenerative TRF receivers into one of the top shortwave receiver producers in the country.
The entire system upgrade of airport communications equipment included General Electric, who got the contract for the new transmitters and Aircraft Radio Corporation, who got the contract for the new airborne gear.National got the contract for the ground-based airport receivers. and his West Coast design team were involved in some of the electronic engineering work of the new receiver that was designated RHM.The RHM was National's first superhet and it had some of the features that were to become National's trade-mark - plug-in coils to select the tuning ranges, a separate power supply and a micrometer-type tuning dial - all of these features were to become standard for National receivers over the next several years.Since the RHM was a commercial airways receiver it had to be built with the best material and best parts available to assure top reliability and performance.Each receiver was hand tested and aligned by engineers at National resulting in a very modern receiver that provided excellent sensitivity and selectivity (along with top-notch image rejection due to its TRF amplifier stage.In 1934, optional 10 meter coils were added as the AGS frequency coverage was increased to reflect the needs of a "ham receiver" - although at $265, not many hams could afford it.
If the ham really wanted the AGS-X he could wait for the introduction of the HRO (in early 1935) at which time Leeds was selling the AGS-X for $123.
Or, if the ham couldn't wait, he could opt for the Hammarlund Comet Pro, the only other commercially built shortwave superhet available at the time.
Frequency coverage of the RHM is 2.3mc up to 15.0mc using a set of 15 coils.
Each band required three coils, RF Amp, Mixer and Local Oscillator which gave the user five tuning ranges. It's likely that less than 100 RHM receivers were built and only a few survive today since most of the airport equipment was scrapped when it became obsolete.
To take advantage of the prestige the Department of Commerce contract had given them (and to profit through additional sales to the general public,) National adapted the RHM for ham use and dubbed it the AGS.
The AGS was upgraded with newer tube types and other changes during its short production life (probably two or three production runs totaling no more than 300 receivers.) The major change was with the introduction of the AGS-X which added a front panel BFO control and a James Lamb type crystal filter to the receiver.