Thanks for the comments Jon.
Another tip, any preamp or active antenna will increase the IMD problem with strong stns (unless there is a good filter in front of the preamp to attenuate the strong stns). Only the very best (and thus expensive) will be useable at LF in my experience. So using a sharply TUNED loop RX antenna, resonated at the frequency you want, might be best.
Roger
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On Jun 25, 2021, at 1:10 PM, JonI via groups.io <ji425bt@...> wrote:
Thanks, Roger. Yes, I sort of surmised this and was looking into bandstop filters earlier today. Disappointed to say the least, especially on a shoestring budget. Too bad I didn't run into these issues more a decade ago when I first acquired the Softrocks, would have been easier to take care of the issues then than now. Back then, just hooked up to the only thing I had at the time which was a 10 meter vertical and did not encounter these issues. Guess the 100 foot wire is just too much. As a last resort, today I added more turns to my indoor active loop to get resonance down below AM broadcast. Maybe this will be enough to curtail the interfering BB frequencies, but the loop still doesn't pick up what the wire does now that I have negated almost all offending noise sources. At least most of my noise issues have been taken care of, which is the most positive thing I suppose.
Thanks for the link you shared. I looked at it and will again not just for the filters but you have other interesting things there too.
Jon
On 6/25/21 2:12 PM, Roger wrote:
I live near several strong AM BC stations and had the same intermod (IMD) problem. In my situation I was operating a modified RXTX on 630 and 2200m. To eliminate the IMD I needed to build a bandpass filter for the bands of interest. See:
and scroll down to Articles, then to the Bandpass Receive Filters.
A high order (large attenuation above 500 kHz) LPF should work also.
Roger
On Jun 24, 2021, at 7:47 PM, JonI via groups.io <ji425bt@...> wrote:
Didn't notice this behavior this afternoon, but tonight I seem to be getting quite a few broadcast station images, especially between 350 to 500 Khz on LF Ensemble. I can still hear longwave beacons, for example, but there may be a broadcast station interferring with it. As far as I know, the band filters are enabled and the proper ones selected in CFGSR. LO is set at 16 instead of 4 like for HF. I'm getting these images stations whether I am on my 100 foot wire or tuned loop.
