VK4AQJ > 17-03-2018, 08:59 AM
VK3QI > 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
(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
(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
VK3RX > 17-03-2018, 01:22 PM
(17-03-2018, 08:59 AM)VK4AQJ Wrote: <snip>
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
VK4AQJ > 17-03-2018, 04:49 PM
VK4AQJ > 30-03-2018, 05:22 PM
VK3RX > 30-03-2018, 06:12 PM
Quote:- 50dB attenuation is something like 50mW for a 5kW transmitter
VK4ADC > 31-03-2018, 07:23 AM
(30-03-2018, 05:22 PM)VK4AQJ Wrote: I had made up a series trap for 927kHz.
I had tried it on transmit previously, and it didn't affect the SWR. When I instered the trap, the strongest station went up to R5, but the QRM was still there. I tried the attenuator. This gave a marginal improvement.
VK4AQJ > 03-04-2018, 12:35 PM
(30-03-2018, 06:12 PM)VK3RX Wrote: Interesting.
You earlier said:
Quote:- 50dB attenuation is something like 50mW for a 5kW transmitter
So I'm surprised that would cause such overload at 3km, but then I've never had a BC station so close. Can you hear the second harmonic on a shortwave portable?
I wonder if the station engineer actually measured and proved the station's compliance. I know with the Mildura situation I described the station had to for the then P&T, but in that situation the interference involved the aviation authority so there was a bit more clout.
VK2ZIW > 04-04-2018, 03:04 PM