Also, at the lower frequencies, noise was always a problem and the TRF circuitry was considered to be one of the "quietest" tuners. The RIO is powered by the same type of power supplies as the AGS used. This particular RIO shown above is serial number 3.It's functional and is a very sensitive low frequency receiver.The AGS-X was tailored for ham needs in that a front panel BFO control and a James Lamb crystal filter were added to the receiver.In late-1934, optional 10 meter coils were added as the AGS frequency coverage was increased to reflect the needs of a "ham receiver" (although at 5 with all accessories, not many hams could afford it.) The AGS-X shown in the photo to the right is serial number F-151 dating from 1934.Frequency coverage of the RHM was 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 only around 100 RHM receivers were built and just a few survive today since most of the airport equipment was scrapped when it became obsolete.
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 contact was identified as 32-15305 and was dated May 12, 1932.
The RHQ was also identified as the AGU receiver in some uses (photo below.) Also, National produced a long wave receiver built along the same lines as these early airport receivers, the RIO (see below.) The RIO was also identified as the AGL.
- Many of the navigational and communications requirements for some airports and various airways stations were not on HF but were on lower frequencies.