WA9ALS MARK-V FT-1000MP Passband Page
Is that strong signal appearing in your waterfall near your desired signal your friend or just QRM? It depends on what filtering you're using and other characteristics of any DSP you might be using! Some rigs have the DSP after the AGC circuit, e.g. an add-on DSP device connected between the rig and the speaker. Others have the DSP circuitry before the AGC. In the latter case, using the DSP to get the offending signal out of the filter's passband will prevent the AGC from limiting your signal of interest. This page is intended to show the effects of a strong signal appearing within the passband of whatever filters you might be using. With the narrow bandwidth of PSK31, many signals will fit within the passband of even a 500 Hz filter - These are only QRM to your signal of interest if you don't have the ability to move the offending signal out of your passband! Imagine what happens when a bunch of people are using only the rig's SSB mic input and their 2.4 KHz filters! These examples were shot in a few moments and are not the best examples one could come up with, but illustrate the point. It's OK to use a wide filter to get an idea where the action might be, but many weak signals will be missed if you don't switch in narrower filters and tune the rig through the area of interest. Then, before you complain about the "QRM" that wiped out the station you were working, try switching in a narrow filter and using some DSP to get rid of the "close" signal. With PSK31, there's room for nearly everyone!
These screenshots were made by using Printkey2000 v5.10 to capture Digipan v1.6d screens. The first 2 examples are of QSOs that were actually on 20M, although the band markers were set for 40M. The discussion utilizes the 40M band markings for reference only. The last 2 examples are from a regular schedule I have with 2 frinds in Indianapolis, and these were really on 40M as indicated.
|500 Hz filter - Here I am working 4Z5JF on 7070.08. Look what happened when a stong PSK signal appeared at 7070.35! It nearly wiped out my DX and eliminated a weak signal just on the lower edge of the passsband. If you look closely, you can see that it also decreased the strength of adjacent signals immediately on each side, as well as that of another at 7070.6. For a larger image, click on the image or here. Friend or QRM?|
|500 Hz filter - Here I am printing 4Z5JF at 7070.08. Again, a strong signal appears at 7069.9 and wipes out my DX. Friend or QRM? This time I used the MARK-V's IDBT SHIFT to shift the passband higher, taking out the "QRM" and restoring my DX. Unfortunately, you can see at the very top of the waterfall that I started to pick up yet another signal at 7070.5 that I didn't have before the SHIFT. For a larger image, click on the image or here.|
|2.4 KHz filter - Here I am working a friend at 7068.8 and there's another signal at 7069.1. I switched in a 500 Hz filter, nearly eliminated the QRM, and my desired signal was even better. Then I gradually adjusted the VRF until I lost the QRM altogether. I continued until I also decreased the strength of the desired signal, but the print was still good. For a larger image, click on the image or here.|
|500 Hz filter - Here's one more example of what happens when a strong signal appears in the passband of even your "narrow" filter. While working the signal at 7069.69, a strong signal appears and nearly wipes out the desired signal. For a larger image, click on the image or here.|