Radio Rag
   

 

 

Pye U450 studio to transmitter link

 

Pye U450 link and VHF FM transmitter in 1981.

Right to left (a) Pye U450 link receiver, (b) 240 volt power supply (c) Microwave Modules FM transmitter with lid removed, (d) Microwave Modules frequency counter, wine bottle and corkscrew! (e) another power supply and (f) Microwave Modules 100 watt amplifier.

 

Pye U450 link and Microwave Modules VHF FM transmitter in 1981

DX100 medium transmitter at Owens Park in 1981. Note the power meter (top) and aerial tuning unit (right). The field telephone (left) was connected to the the studio in another room nearby.

 

Pye U450 link equipment and DX 100 medium wave transmitter at UMIST main building in 1982 (?)

 

  Link Equipment
 

During the 1970s the Radio Rag studio and single medium wave transmitter were located in the same building, usually a student hall of residence, and could be easily connected by cable.

By the 1980s more transmitters had became available and could be used to cover the whole city. In 1981 for example, the studio, VHF FM transmitter and one medium wave wave transmitter (1331 Khz 100 watts) were located at the Owens Park student village. A second medium wave transmitter was located on a high roof 4 miles away at the main UMIST campus. Between the two sites this covered almost all of Manchester.

But this required links between sites. Pete Mann remembers:

"We then decided to use a studio to transmitter link. The only equipment we could find at the time was an ex-Home Office Pye U450 UHF link transmitter. This operated around 435 Mhz and produced 3 watts of RF, and could provide the Owens Park transmitter site with live studio audio at a distance of around 10 miles."

"Unfortunately it radiated almost as much output directly from the chassis on unwanted frequencies as used by the local police! I remember spending a lot of time trying to reduce these unwanted emissions to a manageable level, even to the extent of lining one room with chicken wire and aluminium 'Bacofoil'!"

"We had also acquired another medium wave transmitter, a modified Heathkit DX 100U, and our first FM transmitter which was home built from scrap 'Microwave Modules' circuit boards plus a modified 100W 'Microwave Modules' power amplifier."

"We now had two transmitter sites. Owens Park housed the MK 1 AM transmitter and the studio in another room. We also used the UHF link to remotely feed and control the DX 100
AM transmitter which acted as our back up site at the UMIST main building. The idea being that if the Radio Investigation team turned up at Owens Park we could quickly swap to the reserve transmitter at UMIST in order to confuse 'the enemy'".

"The transmitter switching was performed by sending 5 second bursts of tone over the UHF link. This sounded very professional as we usually closed down by sending the tone. We subsequently received a lot of positive comments about this from our 'Anorak' listeners, without them realising the true purpose for transmitting the close down tone."

I remember the Bacofoil experiment very well, and can still recall a Saturday afternoon with Pete Mann, sticking aluminium cooking foil onto the ceiling. I don't know if it had any effect, but it certainly made the room brighter.

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