There were also several sub-variations on these models. We'll tell you when to stop. The best known copies are probably two German models widely employed as monitoring receivers by the German services, the KST made by Korting Radio and the R4 made by Siemens. These were followed by two solid-state receivers that did not use plug-in coils: Breaking with tradition, the HRO used a frequency counter instead of a micrometer tuning dial. HRO receivers were said to be outstanding and continued to be popular although even better and more expensive general coverage receivers from such companies as Collins Radio became available in the s and later.
- dating introductions examples!
- Dating the Early HRO?
- THE HRO REPORT: DATING THE EARLY HRO!
One can still find HRO receivers dating back to the original model that have been restored by vintage amateur radio enthusiasts and other hobbyists. No S-meters, no crystal filters and most importantly, no external power supply.
Undoubtedly, the Airways companies found the HRO, with its numerous idle coils and separate power supply, somewhat difficult to install and maintain. The RCD and its successors were self-contained receivers only requiring a loud speaker or telephones. This station was basically the aeronautical communications to various airplanes providing weather, flight information and other necessary communications to "in flight" aircraft.
Note that there are "banks" of HRO receivers but notice the three receivers near the rear-most operator. The top receiver is the HRO Junior. Date is probably These receivers generally will have a National Audio Output transformer installed in the chassis area behind the S-meter and adjacent to the antenna terminals. This area of the standard chassis already had mounting holes and lead thru holes for an audio transformer, implying that National anticipated some customers requiring this option.
This would especially be true for many commercial users as well as the military. In fact, some National catalogs do mention that any audio output configuration could be provided. Other than the audio configuration changes, the pre-WWII Navy HROs are standard production types and even have the standard serial number placement and format which implies that the Navy purchased them "as needed" rather than by a large quantity contract.
Generally, most reception stations were separated from the transmitting sites and the decoding sites were separate from either the reception or transmitting sites. At first, Britain couldn't buy the HRO receivers directly, so various methods were used to purchase the receivers. This rather tedious method lasted until Lend-Lease was passed at which time then the British were able to have a steady supply of HROs direct from National.
Many of the HROs sent via Lend-Lease were identified with a double letter prefix to the serial number, e. It also appears that single "P" prefixes with numbers above seemed to indicate HROs destined for duty overseas. The most obvious was the modification of the crystal filter to use an internally mounted crystal, thus eliminating the "easy to remove" crystal that plugged into the top of the filter assembly. There was always questions that arouse regarding the plug-in crystal in that the "air gap" required for the crystal seemed to be interpreted as something "loose" and "rattling around" in the crystal.
The new design crystal eliminated that unwarranted concern and didn't change how the Crystal Filter operated. This type of crystal filter had been introduced in late with National's NC receiver. Initially, these mA meters were only for the receivers being sent to England but later many military HROs had this meter installed. The S-meter "pull-switch" was replaced with a black-finish, ball-handle toggle switch.
Full dates show June 30, Navy RBJ-2 receiver featured 50kc to kc and kc to 30mc coverage with nine coil sets. The lower end of the frequency coverage was kc. The RBJ individual coils four in each coil set are also apparently different than the standard HRO because National assigned them a different number code. The Navy receivers were normally rack mounted and usually were supplied with anywhere from five to nine coil sets that were housed in a coil storage box that was rack mounted. The power supply was a rack mounted type and the power cable from the receiver was a shielded cable even though cloth covered.
by Barry Williams, KD5VC
Loud speaker panels were generally not included in the rack since nearly all Navy operations required headset reception by the radioman. Small ID tags are mounted between the frequency graph and the logging chart for coil identification. In fact, all of the Navy HRO receivers have a multitude of data plates on the coil box, the power supply, the receiver and each coil set. Unfortunately, over the years many of these Navy HROs have been stripped of their data plates making actual identification somewhat difficult without a close inspection.
The set shown belongs to Brian KN4R who supplied the photograph. Other Designations - The U. To further add to the confusion, the U. The Signal Corps versions have a specific data plate mounted in the upper right corner of the panel. There was an HROS that operated on a 12vdc battery system with the power pack which may have been built for Canadian use.
Navy also had the RDG which was a scanning receiver that interfaced with a panadapter. The RDG used plug-in coil sets that are identical to the HRO even using the same individual coil identification numbers. There are certainly many more designations and variations. During WWII, the many variations of the HRO and its accessories were necessary for the various uses the receiver was put to and for the various end-users of the receiver. Some end-users modified their HRO receivers to their specific needs and these receivers were sometimes given new designations.
This receiver was dubbed the HRO They are virtually the same receivers. The common belief was that the all white scale mA meters were exported to England but there were many exceptions to this and the HRO-W is commonly found with the mA meter. Additionally, the S-meter ball-handle toggle switch was replaced with a "bat handle" toggle switch. Sometimes receivers were given a heavy moisture and fungus proofing for severe service depending on the intended location.
The HRO-W didn't have an audio output transformer installed in the receiver.
Even the knobs are MFD'd. Note the gold appearance of the knob skirts and the olive drab appearance of the PW-D dial which is due to the heavy MFP coating. Under the lid is silk-screened data with a place for stamping an application date.
In this receiver's case, the date is JUL 29, Shown in one of the photos in the pamphlet was a technician testing one of the German HRO copies. Also shown was one of the Japanese copies. Both photos are shown below. Later versions of the East German copy used Czech tubes and Russian resistors.
National HRO Receiver
Note that the nomenclature is entirely in Japanese. These copies were not as "literal" as the German copies. Both photos are from "National's Anniversary Photo Album" - published in for National's fifty years in business. Though the AR7 has a micrometer dial and uses plug-in coil sets, that's about as far as the HRO copying went.
The AR7 uses eight tubes plus two in the original PS and covers kc up to 25mc using five coil sets. The tubes employed are standard "American" tube types. The receiver uses a stainless steel overlay on the front panel although some of the Australia Army receivers have the front panels painted green. Interestingly, the S-meter on the AR7 works "backwards.
All AR7 receivers were rack mounted with a rack mounted power supply and a rack mounted speaker. The audio output impedance was approximately Z ohms and Z ohms and the panel jacks provided both audio outputs. Probably around AR7s were produced. Some of the receivers had the LO coil removed from the coil sets and a Crystal controlled oscillator installed for "fixed frequency" operation. Most receivers left the stainless steel front panel overlay unpainted with the nomenclature slightly polished to improve its readability.
Note that the coil graphs are also stamped stainless overlays. Two graphs are used to improve the accuracy of the graph. The coil sets are general coverage only. Most companies were ready to start civilian production by September National, like most other radio companies, offered what had been late WWII receivers as the initial, post-war product line. Note that the other five coils sets are offered at an extra cost.
No wonder it's so hard to find an HRO-W with its complete original nine coil sets. Additionally, the power supply shown in the ad's artwork is the standard and not the heavy-duty "W" version. As expected, the coils sets are "J" version non-bandspreading types. Updates from National seem to come at a leisurely pace and by early the HRO-5 had been upgraded to have the A,B,C and D coils feature the bandspread function.
National designated this receiver the HRO-5A.
One in the arbitration period dating the early hro?
This is a very late version of the receiver made well after June featuring the square S-meter made by Marion Electric which was used to conform with the S-meter used on the NCD receiver. Also, this receiver has the later cadmium-plated chassis and the six-step Selectivity control for the Crystal Filter operation. Note the increased spacing between the two Crystal Filter controls. The HRO-5A1 was introduced around March although this receiver is still basically built from mostly "left-over" stock.