The Quintessential HRO by John Ridd G8BQX

Thanks for your promulgation of the information on the HRO. This was truly and excellent receiver.

Herewith copies of the British military documents on the beast, which will perhaps demonstrate the actuality, it not the history, of the HRO in military usage in ‘Wireless R’ and ‘SCU’ vehicles.

There is some more information regarding maintenance, adjustment and the British power supplies.

Take no notice of the issue dates of the documents, which bear NO relation to the dates the equipment was taken into service. The circuit diagrams of the receiver and coil units are on several fold-out sheets in the original. I have supplied sufficient overlap sheets to cover the joins.

My only personal experience with the HRO was as an Investigation Officer in the Post Office Radio Service. More than a few Television Interference cases – impute to the ill-will and general malefaction of licensed Radio Amateurs – were found to be due to excessive harmonic radiation from the local oscillator in the HRO.

This was sufficiently strong to cause TV Interference in the 45 Mhz nominal vision bandwidth of the TV on Channel 1, as was available in the South East of England. Not that the HRO was the only receiver causing trouble : the AR88 could also give QRM in some installations, as could other ex-service receivers. The answer was to incorporate extra filtering in the power leads inside the HRO, filtering of the loudspeaker leads, and, perhaps an extra low pass filter in the aerial lead to the receiver, just to reduce the radiation of oscillator harmonics.

It is notable that few contemporaneous receivers of Naval origin caused such problems. It appears that the Navy were very aware of the dangers of local ocillator leakage, not only because of the likely effect between many receivers in the WT Office of the ship (which were, effectively, all within the same screened tin box,) but also because radiation from local oscillators in a ship might be received and located by direction finding from opposing forces, resulting in a malevolent assault of a highly explosive nature!

73 John Ridd G8BQX June 2007.

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Popular pages

Get your amateur radio licence - Find out more about amateur radio licence training.
Month on the Air - G3MGQ's popular monthly DX contest/expedition list.
Wilf Gaye Memorial Cup - The clubs annual operating event in the memory of Wilf Gaye M0GYE.
St. Richard's College Buildathon/STEM/ARISS - HERC attends St. Richard's Catholic College for their various events surrounding the Tim Peake ARISS contact.
G3BDQ - John Hey's Rare QSL Cards.
Sussex Electronics Radio Fair - SERF Sussex Electronics Radio Fair 2016.
Vital Spark - A selection of articles re-published from the Vital Spark.
RSGB News - Find out how to get RSGB news on your mobile or PC.
Experimenters Corner - A selection of Proteus projects by Bob Gornal (G7DME)
BBADL - Bath Based Distance Learning Course.
Conquest Hospital Radio - Presented by HERC member Antony (G4CUS).
Radio Rallies 2016 - An up to date list of radio rallies scheduled for 2016.
Club QSL Cards - A selection of QSL cards the club has received over the years.
Other Newsletters - Excellent newsletters and magazines from other clubs.
TX Factor episodes - Take a look at the TX Factors YouTube videos.
John Taplin - A bio of the late John Taplin.

Amateur Radio Resources

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