17-03-2018, 09:15 AM
(17-03-2018, 08:59 AM)VK4AQJ Wrote: I have a problem with this one local broadcaster on 927kHz AM. it's about time they phased out MW AM like they are doing in Europe. The sound quality is abysmal anyway. (rant over). That's the only one that causes problems for me. Being local, the strength of the signal is obviously swamping the bandpass filters in the rig.
I have had thoughts about using an L-C series resonant circuit at 927 kHz. So the 927kHz signal would be intercepted and sent to ground.
I've seen examples of high pass filters being used, but I also operate on 630m, and don't want to have to switch the filter in and out every time I change bands.
Has anybody else had experience with eliminating AM broadcast QRM? I will probably have to use a relay circuit to bypass the filter on transmit.
The other concern is that even though the second harmonic from the broadcaster is reported as 50dB down, that may not be enough, and no amount of filtering at 927kHz will address a second harmonic at 1854kHz.
- Jim
Jim,
Before you get too carried away with filters etc. do a couple of other things:
(1) do a distance/attenuation calculation of what level the second harmonic may be at your qth from the broadcast station
(2) do a search in your neighbourhood for any possible "rusty bolt" type of rectification that might be reinforcing the harmonic at your qth.
Also ask yourself is the level of interference is weather or temperature dependent? That may give you a clue as to whether the problem is external to your qth or not.
Cheers
Peter VK3QI
(17-03-2018, 08:59 AM)VK4AQJ Wrote: I have a problem with this one local broadcaster on 927kHz AM. it's about time they phased out MW AM like they are doing in Europe. The sound quality is abysmal anyway. (rant over). That's the only one that causes problems for me. Being local, the strength of the signal is obviously swamping the bandpass filters in the rig.
I have had thoughts about using an L-C series resonant circuit at 927 kHz. So the 927kHz signal would be intercepted and sent to ground.
I've seen examples of high pass filters being used, but I also operate on 630m, and don't want to have to switch the filter in and out every time I change bands.
Has anybody else had experience with eliminating AM broadcast QRM? I will probably have to use a relay circuit to bypass the filter on transmit.
The other concern is that even though the second harmonic from the broadcaster is reported as 50dB down, that may not be enough, and no amount of filtering at 927kHz will address a second harmonic at 1854kHz.
- Jim
Jim,
Before you get too carried away with filters etc. do a couple of other things:
(1) do a distance/attenuation calculation of what level the second harmonic may be at your qth from the broadcast station
(2) do a search in your neighbourhood for any possible "rusty bolt" type of rectification that might be reinforcing the harmonic at your qth.
Also ask yourself is the level of interference is weather or temperature dependent? That may give you a clue as to whether the problem is external to your qth or not.
Cheers
Peter VK3QI
(17-03-2018, 08:59 AM)VK4AQJ Wrote: I have a problem with this one local broadcaster on 927kHz AM. it's about time they phased out MW AM like they are doing in Europe. The sound quality is abysmal anyway. (rant over). That's the only one that causes problems for me. Being local, the strength of the signal is obviously swamping the bandpass filters in the rig.
I have had thoughts about using an L-C series resonant circuit at 927 kHz. So the 927kHz signal would be intercepted and sent to ground.
I've seen examples of high pass filters being used, but I also operate on 630m, and don't want to have to switch the filter in and out every time I change bands.
Has anybody else had experience with eliminating AM broadcast QRM? I will probably have to use a relay circuit to bypass the filter on transmit.
The other concern is that even though the second harmonic from the broadcaster is reported as 50dB down, that may not be enough, and no amount of filtering at 927kHz will address a second harmonic at 1854kHz.
- Jim
Jim,
Before you get too carried away with filters etc. do a couple of other things:
(1) do a distance/attenuation calculation of what level the second harmonic may be at your qth from the broadcast station
(2) do a search in your neighbourhood for any possible "rusty bolt" type of rectification that might be reinforcing the harmonic at your qth.
Also ask yourself is the level of interference is weather or temperature dependent? That may give you a clue as to whether the problem is external to your qth or not.
Cheers
Peter VK3QI