Sam Hunt (who owns Maxxwave) writes: It's a 30ft high vertical antenna in fibreglass tube with top-loading. The ATU is a single coil with variable tappings, giving about 150khz bandwidth at -15dB return loss. It's a very awkward design to work with (especially to tune) but has very low loss and excellent bandwidth for a short antenna. It's not a frequently used design because it's difficult to work with but once installed is very stable, partly due to the wide bandwidth and lack of capacitors. Both antenna and ATU were made by Maxxwave and are very similar to that used on Seerah 1575. I understand this design has also been used on some BBC short antenna installs.
Transmit power is 50mW EMRP, but this spectacularly fails to deliver good quality audio over the intended area so we have asked for a power increase - the next lowest power AM station is 1000mW, so we are licensed for 20 times lower power than any other service in the country. We have a lot of electrical interference from CCTV cameras, etc.
The audio processor again is a Maxxwave product, with 32767 band compressor and careful look-ahead limiters and controlled distortion clipper. This somewhat mitigates the very low power by bringing the audio level up, and gives good flat audio response down to 35hz - something AM does tend to do better than FM.
Fundamentally the transmitted audio quality is good and it sounds good in the right location, but reception overall is problematic due to the very low EMRP.
Distant coverage is very limited by 1449 Asian network from Peterborough with coverage disappearing completely less than 3 miles in the Peterborough direction, but this is not really an issue within the intended service area, which is more limited by high electrical noise. |
