Hi Fred B,... Totally agree, Ofcoms map for 648, looks like they drew round their Coffee cup
The strange thing about Ofcom calling their maps "MCA" for Measured Coverage Area is...
They are NOT Measured!... But are actually a Computer Simulation, using some quite good software

We ought to credit whoever it was on here, for original numbers, he posted levels, right round
from The Wash (near Hunstanton, on the North Norfolk coast) right round to the west, and then
right down to Northampton... I plotted these on a Google map, and It all made perfect sense


When I worked at KCBC AM yonks ago, We had the TX on air, and Ofcom came with their Vehicle
to measure the signal levels, The Same day, I went out and did my measurements, every 10 degrees
(so I could draw a Polar diagram of the coverage)....To my surprise, I drove along a Road, to See
Ofcom Parked in a farmers gateway, to do a measurement

To my amazement, I saw the spot they were, was Right Under some Low Overhead Wires,
(Local Electric I think) Anyone who knows about this would know, It messes the readings up...
(In fact, if the wires are running in the Direction of the TX, It Increases the Signal Level)
So must have been a trainee Ofcom chap suppose...

With a Simulation for the 5 mast array, could try diff. things Like, using a Different mast
(not just the centre one) Could try Grounding some feedpoints on other 4 masts, to see result
Possibly a simulation, could produce a Nearly Omni-directional result, worth a try

In the USA, a firm does Detuning of other masts, to reduce Nulls and directional problems for AM
At KCBC we had a Null in one Village direction, caused by HV Pylons on the Industrial Estate

Rod Watts