The National NC-100A is an after-successor of the famous HRO. In contrast to it's ancestor, it doesn't make use of plug-in coils anymore, but is is equipped with a "coil catacomb": the receiver coils are moved in the bottom receiver be means of a slightly complex but high quality mechanism: the coils are moved like in a drawer and contacted very well - a high quality, but also pricey variant of a bandswitch. The NC-100A comes with a direct reading dial in contrast to the logging dial with micrometer mechanism of the HRO. Both variants have their advantages but also their drawbacks, that's why HROs and NC-100A have been produced in overlapping years.

The main tuning knob is located in the middle of the frontpanel, just below the semicircular dial. A mechanically moved pointer indicates the active frequency band. The main dial has calibration marks to read frequencies directly, it also has a 1-1000 logging dial. The coil sets in the drawer-like "coil catacomb" at the bottom of the receiver underneath it's chassis is moved by the big bandswitch knob, one rotation for 360° will move the coils in position for the next band segment.
At the left of the frequency dial, delow the signal strength meter, You find the operation switch with the positions OFF (receiver switched off) - B+ OFF (valves heated, plate voltage switched off, to be used for standby and whilst bandswitching) - B+ ON for normal operation. Just below, you find the RF gain control.
The controls for the noise limiter (turned off in "O" position) and the tone control are located in the left lower part of the front panel.

At the right of the frequency dial, you find the switch for automatic volume control AVC, manual gain control MVC and a third position for the reception of telegraphy / CW signals with MVC and the BFO activated, Use the C.W.OSC. control in the right lower part of the front panel to control BFO pitch.
The volume control A.F.GAIN CONTROL is also found at the right of the frequency dial below the AVC/MVC switch.

The National NC-100A is technically a single conversion superheterodyne with an RF preamplifier stage. The signal coming from the antenna will first pass a tuned circuit an the RF preamplifier (V-101: 6K7) and the be mixed with the oscillator (V-103: 6J7) signal in the mixer stage (V-102: 6J7), the intermediate frequency of 456 kHz is generated.
After two IF amplifier stages (V-104/V-105: both 6K7), the signal is demodulated in the detector stage (V-107: 6C8G) it's second system will be used in the limiter stage. The AF preamplifier stage (V-106A: 6F8G) is followed by the AF final stage (V-109: 6V6G) which will drive a high impedance speaker. For reception of CW morse codes transmissions, the signal of the beat frequency oscillator BFO (V-108: 6J7) is injected before detection.
In contrast to the HRO, a power supply using a 5Z3 (V-110) as rectifier tube is integrated in the cabinet.

According to the list of receivers used by the Swiss Army, several variants of the NC-100A have been in use:

• E-616: National NC-100XA (with crystal filter)
• E-617: National NC-100XSA (with crystal filter and external speaker)
• E-618: National NC-100A