Good table-top receivers have a suite of tools available for fighting off interference. Besides bandwidth choices, ECSS reception and passband tuning, the user can choose to employ automatic or manual notch filters at the audio or IF level, noise blankers and noise reduction functions. We need any function that can enhance the signal-to-noise level of the desired station, and often if one tool doesn't work, another might.
Portable receivers usually lack many (or all) of the interfering fighting tools. Alas, that is the case with the E1 as well. As stated earlier, its ECSS tuning is very good, but ECSS must be regarded as a rather compulsary part of an HF receiver today. AM Synchronous Detection is quite good overall, but not suited for DX-ing narrow splits. So, what do we have?
According to Eton's specs, there are three bandwidth choices; 2.3 (sometimes referred to as 2.5), 4.0 and 7.0 kHz. The 2.3 is apparently the muRata CFJ455K5 which is mounted in a large number of receivers. I don't know the origin of the other filters. Judging from audio recovery, I'd say the 4.0 is more like 4.5, and the 7 is more 8-ish. I hope someone will take the time to measure the correct bandwidths and the shape factor. They appear to have good ultimate selectivity though. There's nothing wrong with the filters except my personal preference would probably be less than 4, and 6 kHz for the two wider filters. Other people with other preferences will surely disagree. Actually, a portable with a choice of three mode-independent, good quality IF filters must ble close to one of a kind.
Passband Tuning (PBT)
Something we cannot do without! In SSB (and ECSS of course) , PBT allows for moving the IF passband of the receiver relative to the detector BFO (mostly quoted from the manual). The PBT can be tuned +/- 2 kHz. For reasons mentioned below, the PBT is in more use on the E1 than on my other receivers.
The manual is rather inconclusive about the PBT and AM. On page 24 it says "PBT also functions in AM and AM SYNC modes, but in these modes it act primarily as a frequency offset, which can also be accomplished with the 'TUNING' knob". If we're to believe this the PBT control in AM is identical in function to the Tuning knob! However on page 15 it says "The PBT (...) knob varies the IF passband of the receiver plus or minus 2 kHz (...) relative to the displayed frequency when on AM Mode". When I use the PBT in AM and compare it with off-tuning using the Tuning knob, the audible results are identical. So, is the AM PBT an IF shift, or is it off-tuning?
A Notch Filter is an essential tool for removing heterodynes. Any notch filter will do really, even a basic audio notch filter - but the E1 has none. That is in fact a major drawback with the radio. Removing or reducing hets can to some extent be done by using the PBT, but that is 1) time consuming and 2) can result in increased interference from a different source.
A Noise Blanker is also missing. Ignition-type noise, and in my case Loran C ticking, can be reduced with a good noise blanker.
And there is no Noise Reduction function. Although we have seen many of questionable quality, and that they often degrade the audio quality, in some instances they really do help.
Obviously, here's where the tabletop and the portable go separate ways.