Susy Radio 531

Until 2001 Susy did two FM RSLs per year but in the early noughties there was a financial downturn. So why the move made to mediumwave? Colin Pearse elaborated “we’d thought of a one-off AM transmission in the late 1990’s but not enough advertisers could be found for this extra broadcast. The decision to go for AM in 2001 was down to economic reasons the AM license being half the price of FM and with the downturn not enough sponsors were initially forthcoming to cover a month’s FM costs”


The station has always prided itself on the fact that engineering has always been carried out “in-house”. This led to another course of revenue as technical assistance and broadcast facilities over the years have also been provided to other broadcasters including Reigate Festival Music, Justice FM (West London Youth Project), Medway FM (Rochester), Radio Redhill (Hospital Radio Service), and Redstone FM until early 2006.


The decision to go onto AM was greatly aided by a couple of events as Chief Engineer John Stockley (Radio amateur G8MNY & GB7CIP) explains “we had also been given access to a site at the Community Centre in Merstham, Surrey with large trees and space for a decent aerial and had also been gifted a transmitter by National Air Traffic Service at Gatwick”.


A deal was negotiated where SSRG (Sussex Surrey Radio Group) converted the attic space at the Community Centre into radio studios for their Youth Service. John and Mike Roach designed them and Colin Pearse provided the woodwork for the desks. The station also donated £1,000 for the youth radio project and provided transmission facilities, which has transmitted under various guises latterly as Spin FM.


The donated transmitter was a former Decca Transistor longwave unit. Theis was an ex Morse code aircraft beacon with a maximum rated output of 400 watts PEP max on 531 kHz. This unit had to be considerably modified for AM broadcast use. In this form having a maximum power theoretical power rating of 160 watts. About 50 watts AM carrier required for 1W ERP. 


In the photographs the transmitter is in its original location on the ground floor of the Centre. The equipment latterly being re-housed into an alarmed converted outbuilding in purpose-built racking. The original rig became a standby unit as a second transmitter was sourced from NATS and re-built to a different standard. The original has since been upgraded too. As you can see from the photo alongside the transmitter was a regulated power supply with a large electric fan trained on it for additional cooling in the hot summer.


The audio processor was donated by Trevor Brooks former operator of the short-wave based trade station Radio Fax. This processor had an interesting provenance as the heart comes from Radio Fax. The unit being re-boxed for Susy Radio. In addition Tony Collis provided assistance. Tony being the former engineer of famous land-based pirates Radio Kaleidoscope and Radio Jackie back in the 1970’s and early 80’s.


Most AM RSLs had opted or were given frequencies of 1269, 1278, 1287 kHz or 1602 kHz (in the south east of England for example think of Ravensound from Bromley, Air Fayre Radio from Biggin Hill etc. Susy requested 531 kHz 565 metres. This provoked some internal discussion by Ofcom and it was agreed on technical grounds. With a signal on 531 capable of 3 times the distance of a comparable power on 1593 kHz it could result in a theoretical 9 times larger area and therefore potential listeners. This led to some to repercussions a few years later.


Aerial Design Susy Radio utilised an “inverted L” with a 45° sloping vertical underneath the top section. John Stockley advised this was “very effective with no horizontal polarisation.” The aerial was raised utilising the traditional pirate radio method of catapult firing fishing line with weight to take the first part 20 metres over the best available tree. This being the maximum vertical height allowed under regulations. If you ever watched the DVD “Free Radio – the story of clandestine radio in the UK” the re-creation of raising a pirate medium wave aerial was carried out in the youth centre grounds by local youths wearing 1970’s wigs!


The top two wires were approx 90m long 2.5mm diameter, tied up in the tall trees with a mean height of 20 metres and held really taught. The sloper consisted of 10 spaced wires of 1.5mm diameter all 20cm spaced. Three plastic pipes were used as spacers for the risers and weight stabilised top spaces. The transmitter output being fed through an insulator (in this case a converted water butt) to two insulated feeder cables.


John pointed out that the aerial height is only 1/7th of a ¼ wave explaining the maximum gain is around 2% (1/7 x 1/7) -17dBi as it is only base loaded. The figure being close to the radiation resistance method of calculation of 2.9%.


The earthing system consisted of a centre stake 1.5m 22mm copper pipe  with 12 x 1 metre 22mm diameter copper earth pipes arranged in two circles of six in a hexagonal pattern. The outer being at 2.5 metres from the central stake. Joining wires connect each set of six pipes into a circle, with six ground radials interconnecting both sets of earth rod rings to the centre.

The earthing has been experimented with over the years but John advised that “adding any more did not effect the aerial Z at all and adding 463 foot counter poises had no effect either”.


Since the first mediumwave transmission in 2001 the system remained essentially the same. After the first year the feed point was also moved higher up the vertical element as a precaution on safety grounds. The system survived being cut down by vandals in 2002.


In 2005 with transmissions starting that August Bank Holiday Weekend the RIS turned up days later at 9 o’clock on the Thursday morning requesting access to the site. Such a visit is a rare but not an unknown occurrence. Care 1278 AM was checked over in the 1990’s and former FM pirate Starpoint was “raided” in Windsor in the early 90’s. The operators waving their RSL license as the authorities came in the door!


On the Tuesday a complaint was made to Ofcom that the station was getting out far too well. So the following day a RIS (Radio Interference Service) mobile team had made field strength measurements and all came within the anticipated parameters. Despite this they still turned up at 9AM on Thursday to the site. The Breakfast DJ letting them in and calling up boss Colin! The RIS team were a friendly bunch who seemed to enjoy the day out and the gratis coffee and biscuits. They were very satisfied with the Susy operation – giving it a totally clean bill of health - it would seem that someone in Ofcom’s officialdom forgot that with topband AM RSL’s licensed to provide an expected coverage area of 5-8 km our lo-band could be expected to cover 15 to 24km! That’s a daytime figure the service area being reduced to 3km at night.

Susy didn't have a copy of the licsense show them to broadcast and explained to the RIS we had other correspondence to support that we were legit. The RIS had us on their list as approved and explained that Ofcom were about 6 weeks behind on their paperwork. It did turn up within days and was proudly displayed outside the studio!


With a number of station staff being former pirates from the Seventies and Eighties, a D/X programme for the radio enthusiast was aired as well as relays from the local night club on a Saturday night.


After a 5-year absence in 2006 Susy returned to FM on 87.7 MHz, to promote The Variety Club of Great Britain






Aerial 2001

531 Transmitter and Audio Processor

Colin Pearse

Ray Adams at work