[trh01uk]

There is something odd going on here - and I doubt its going to be fixed by a filter in front of the receivers. For one thing these MW signals are being picked up on the tropical broadcast bands (4750 - 5060kHz I think?) and also LW (153 - 279kHz?) and apparently on a wide range of receivers, from vintage to modern.

Spurious signals generated in the receiver itself depends on non-linearities in the front-end. These are going to vary enormously from one set to another, particularly when comparing vintage with modern. Unlikely - in my view - unless in fact the OP is located very close to a MW transmitting site? In which case its possible what is happening here is simple overload or blocking of the receivers. Most receivers need hundreds of millivolts to suffer from this problem and that would require a close-by MW transmitter.

I am thinking its more likely that there is some non-linear device outside the receivers, which is generating a wide range of mixing products. It has to be a wide range - because its affecting both LW and 4 - 5MHz. My suspicion in the first instance falls on the "amplified antenna" that the OP mentions. That's going to be a wide-band amplifier without any tuning, presumably to match the antenna to a piece of coax? That could be generating such mixing products even if its not connected - with its output cross-coupling to the actual antenna in use.

My advice would be to

1. Switch off the amplified antenna - ideally remove it from circuit altogether, because it could still generate mixing products even when the power is removed. Then see whether the problem disappears.

2. If step 1 makes no difference, then take the IC-R75 receiver, and set it up to demonstrate the problem of a MW station being picked up on 4 - 5MHz. Then switch in the 20dB attenuator that I see is available on this set. What difference does that make to the unwanted MW signals?

3. If both steps 1 and 2 fail to make any difference, then give us some more information. Give us precise frequencies that you are picking up a specific MW station. Does the same station appear on both LW and 4 - 5MHz? If so what frequencies do you detect it? What MW station is it?


Richard