[Milsurplus] Re: [The WS No.19 Group] Re: [ARC5] What did they talk to ??

[Brian Clarke]

Hi John,

Here is a view that I have developed over the last 50 years.

If you look at the development of comms with aircraft, the driving force was the US Postal Service, which 
by 1930 was losing aircraft and mail hand over fist, and not knowing until the aircraft didn't arrive. So, Dr 
Drake, of what became the Aircraft Radio Corporation, developed his small superhet sets at a time when 
David Sarnoff was screwing Edwin Armstrong into the ground; Drake could see what Sarnoff couldn't - 
Drake realised the Armstrong ideas but didn't have the components; so he set about designing and 
manufacturing them himself. During WWII, these sets became the ARC-5 - but he got overloaded and 
Western Electric stepped into the breech to produce clones, known as the AN-SCR-274N series. The 
Hallicrafters [?] BC-610 was already around as were the R-1155 and T-1154, so inter-service 
intercommunication on HF AM was no technical problem - the main problem was political, getting the 
uneducated officer corps to develop bandplans and frequency plans. Nobody had bothered with W D 
Scott's ideas about selecting officer material based on skill and knowledge - they were still being selected 
for their heritage, and their ability to afford their saddles and expensively-cut uniforms.

If you look at the technical development of radio during WWII, you get one view - ie, that VHF was initially 
considered impossible. I even have a book titled 'Ultra-High frequency techniques', written for training radio 
techs during WWII, that sees VHF reaching all the way to 50 MHz. Wow! Later in WWII, the Americans 
developed a VHF set that was clunky and difficult to manufacture, while the British developed what was 
to become the SCR-522. Unfortunately, the Americans copied the British design very faithfully, including 
the use of rotten muck-metal in the connectors. Now, Edwin Armstrong's ideas were really taking off!

Then if you look at propagation, you get another view - in WWII, you see HF used for ground-to-ground and 
ground-to-air, while VHF, was used for air-to-air - where the horizon is much further than the 15 miles you 
might get from a ground-mounted tower - and for ground-to-air when aircraft were in landing or takeoff 
mode. At last, people were waking up to the propagation capabilities of VHF from an elevated weapon 
platform. In later political mistakes, eg, Korea and Vietnam, VHF was used for ground-to-ground just 
because of its limited range so the enemy could not intercept. Scanner-based RDF became so good that 
you didn't dare use a VHF radio while you were wearing it for fear of becoming the permanent owner of a 
new see-through navel. Hence, the development of remote control via telephone lines for the PRC-9, -10, 
-25, -77, and so on - put your radio up in a tree and operate it from down in a bunker.

This may not answer your question directly, but if you use the propagation equation, and set height of Tx 
and Rx at say 10 k and 20 k feet, you'll soon see the horizon expand. Then put in the free-space 
attenuation and you can work out how far 10 W from a SCR-522 can get. The propagation equation is 
covered in detail in the RSGB Handbook and in many of Arthur Collins' books on radio communication.

73 de Brian, VK2GCE.