attenuation of input disturbances

[IU8OGE]

I apologize if this question is useless but not being an expert I try to ask.

All portable radio and in particular the Chinese including the GD77 suffer, with external antenna monted and in particular on the 2m band, and they become deaf.

this problem is caused by the interference of FM or TV repeaters and is only noticeable if you live in large cities or near repeater bridges.

The problem is solved at the hardware level simply by inserting a notch filter (band size) that excludes 88-108mhz reception cut at 98mhz

The question is:

Via firmware it's possible create a function that solves this problem? maybe it can be activated and deactivated?

thanks,
Diego

[OE1MWW]

Your wish and your idea may sound reasonable - from a point of view of a user.

But those interference happens at the 'front end' (input stage) of the device, the
firmware has only control of frequency selection and demodulation of a signal.
A 70 $ mass production device, like the GD-77, lacks of all the extensive filter
hardware at the antenna input you may find in much more expensive devices.
Filter for that purpose are 'selective filter' and not 'notch filter'. And only those
selective filter (L & C) at the input stage of a receiver could prevent interference
and can create radiation resistance of unwanted signals.

It's impossible to do that with the firmware of the GD-77

73's de OE1MWW
Wolfgang

[IU8OGE]

Your wish and your idea may sound reasonable - from a point of view of a user.

But those interference happens at the 'front end' (input stage) of the device, the
firmware has only control of frequency selection and demodulation of a signal.
A 70 $ mass production device, like the GD-77, lacks of all the extensive filter
hardware at the antenna input you may find in much more expensive devices.
Filter for that purpose are 'selective filter' and not 'notch filter'. And only those
selective filter (L & C) at the input stage of a receiver could prevent interference
and can create radiation resistance of unwanted signals.

It's impossible to do that with the firmware of the GD-77

73's de OE1MWW
Wolfgang

Thanks