2 METRE INTERFERENCE | THE HIDDEN PROBLEM 

Thanks. You are most welcome!

Thanks. I was having a bit of fun. However it’s a very real problem.

I think it's very common.

Thanks!

It's really hard to detect sometimes!

It's a more common problem than many suspect!

Thanks for the feedback and suggestions. However, a quarter-wave co-axial stub will have such a low Q factor that in many cases it will make no discernable difference.

The FT270 is likely to have good front end filtering.

@@g3cwi_Radio_Adventures I definitely think this was something that was needed in the SOTA space as lots of people with inexpensive starter radios start getting into the hobby.

Thanks - I did forget to include a directional antenna in the mix though!

Richard Newstead Well that would raise the interesting issue of what design of antenna to use, that will be directional across a wide range of frequencies. I guess the log periodic would qualify, but I don’t think they have enough off-boresight rejection, as on any given frequency they are really only as good as a 3 element yagi. At one site in Canberra I have had some success using horizontal polarisation instead of vertical (at both ends of the contact), but I don’t know whether that was successful due to increasing the signal strength on 2m or happening to reduce the level of local unwanted signal. Your demo of hearing the incoming 2m signal with the attenuation of an unconnected plug was perfect, showing that the receiver is fine until the high strength local qrm was fed into it. Beyond the scope of a demo is the question of what blocking is. As I understand it, it is due to the dynamic range of the blocked stage (either RF amp or possibly mixer) being exceeded by the strong local signal, meaning that the amplifier spends most of its time either saturated (on positive peaks) or cut off (on negative peaks). It is being switched at the frequency of the qrm signal between those extremes. In the presence of multiple input qrm signals on different frequencies it is likely that the combined instantaneous signal level is always above the amplifier’s saturation level, therefore the amplifier has zero gain. (Vk1da)

@@andrewd4890 Yes. I did wonder about that myself. Also small antennas optimised for gain often have a relatively poor f/b ratio.

Now you know!

Might actually be worse if they are across the valley!

Thanks Alan

The filter is only rated for 5 Watts so really dsesigned for handies.

@@g3cwi_Radio_Adventures OK, thanks!

No unfortunately you can’t

People suggest that the FT60 is one of the best.

Yes it will also reduce spurious emissions.

5 Watts - check out the product description!

Mavic Mini here < 250 grams.

If you suffer from this type of interference - yes.

Better in that you dont have to make it!