cys wrote:Thanks, this is what I was thinking in terms of interference. I wanted to see what others thought though. I will say that I just watched a Youtube video by Flex Radios Inc and the clear message was that this was not supposed to be possible... based on their simulation.
I'm not familiar with that video. Perhaps you could post a link? I suspect whatever Flex is discussing it's not relevant to this problem. Co-channel is co-channel and, if it is bad enough, will cause small signal suppression and non-linearities in nearby receivers.
To hear stations that are sometimes just imperceptibly above the noise level, I use diversity, NR2, NB2, ANF and SNB. I use headphones. I push the gain beyond what most people do, and what the manual suggests to capture those stations that are barely audible above the noise.
I hope you mean you use these DSP features appropriately, not all at once. NR2, NB2 and SNB are all designed for different kinds of noise, and rarely, very rarely, is it the case that more than one of those processing modes is necessary at any one time.
Since you are a low-SNR signal hunter, if band conditions permit, you can obtain a couple of more dB of performance by disabling dither and random features of the ADC (it's in the settings). However, that is absolutely the last thing you should do if there are other large signals on the band. Receiver IIP3 is
substantially improved with dither and random both activated. That is why it is the default setting.
My main antenna is a rotatable dipole that can't rotate much at present due to trees. My second sense antenna is an end fed dipole that is orthogonal to my main antenna.
Yes, that's not a well-behaved, easy-to-model, beamforming array like two verticals would be. All I can say is that if it doesn't allow you to tune a null in that station's direction you may want to try something else.
By posting here I'm trying to assess how much of the interference is splatter from overdriving his amp and how much is due to how Thetis and the 8000dle deals with a 1.5kW signal half a mile away on the same band.
This is an impossible scenario for any radio, and the behavior you are observing from your radio (comprised of Thetis and the 8000 hardware) is not at all unreasonable. Switching to another radio will not fix this.
If I glean from input here that it might be worth approaching the station about the possibility of easing up on the IMD and splatter, then I can do try to do that.
That's exactly what I'm suggesting. If this gentleman cares about the quality of his signal perhaps he has a station monitor or oscilloscope. It would be easy to show that his amplifier is being driven into saturation. However, as I wrote previously, that can be a hard sell to a lot of folks. They care about their
audio quality but not necessarily their
RF quality, and if they don't see that needle or LED pointing to 1500 then it's no good. The reality is that you should rarely see the power go much above 1000W, even on a so-called "peak reading" power meter. The 1500W peaks are just too fast to catch without a scope.
I wonder, however, how does his signal look further away? Have you tried monitoring him on a remote, web-SDR? It might be an interesting bit of data. If it looks bad there then it's not just you.
Added note: I did try putting a 20kHz notch over his immense signal and it didn't help with the interference across the remaining band.
That will have no effect. It is not prior to the preamp or ADC. Remember, this is co-channel interference, i.e. in-band interference. There is no preselection (bandpass) filter that is protecting you on any ham radio, including the 8000, because you are both on the same band. Thus the preamp and ADC (or, if this were an analog radio, the first preamp, if any, and the first mixer stage) are getting hammered and
nothing the radio does after the front end will matter.
You could try to build a very sharp, very narrowband RF notch filter at the freq. he normally operates on, but such filters are very hard to realize in practice.
Also, it would not be surprising if you are suffering receiver performance degradation on other bands. The preselection filters on all Apache designs are only third order, not seventh order like you find on many "contesting" radios. Those third order bandpass filters don't do a lot to protect the preamp and ADC from anything DC to 60MHz.
