Thank you for your input John. Indeed I’m already convinced by the filters, on my sota rig I have them electronically, I can tune them on the go as I want them to be. It’s fantastic !
I will check the second hand market for a few weeks and see if good opportunities show up locally !
I learnt my trade using a home brew RockMite so I feel that I’m pretty decent at filtering signals using my ears. I got a 300Hz CW filter secondhand for my FT-817 and I really like it. The filter is Yaesu brand and supposedly they’re more like 500Hz anyway due to the skirts.
I tried a NEQRP NESCAF kit with my RockMites and the results were impressive to be honest, better than I expected.
I built myself a SCAF unit on a tuna can for my QRPp rigs and it works well.
An IF filter is the best option (beyond training the ears) but an AF filter can definitely help.
73, Colin
Wow I love it !
As I tried to explain before, my problem is not with isolating the signal in my head. The problem is that I cannot stand the QRM. When someone is sending through a very busy band and as chaser I don’t make contact in the first minute or so, I just quit. All the high pitched beeps from the stations above are killing me.
Using lower fidelity headphones helps with the high frequency stations.
While I like crystal filters in my rigs, I find that adding some audio filtering does make things much more tolerable, as it also removes noise that gets added after the detector stage.
And for very weak signals, my old analog(ue) radios with crystal IF and op-amp audio filters are still my preference: they are devoid of the digital “crud” that I hear in the digital equipment.
Is an external audio filter perfect? No, especially not when strong signals outside the passband still affect the AGC. But they can help a lot with the hearing fatigue.
Perhaps you could try a resonant speaker, like a large piezo disk in a cavity?
Small ones are a fairly high resonant frequency, but this one is 1Khz. Perhaps that is OK, or perhaps lengthening the helmholz resonator would lower it.
Perhaps start with a large disc and just make the resonant cavities.
If you have two at different frequencies (e.g. 600Hz left, 800Hz right), do you get a sound stage effect that also helps?
Has anyone got experience with used a stereo phasing sound stage effect where the apparent position moves with pitch?
I wonder if any of the old reed/tuning fork selcall / squelch filters would be useful if they were coupled and damped?
These are a steel reed with a piezo transducer about 20mm long. I think they responded to a steam whistle.
I have 592Hz,622Hx,727Hz in the drawer. They are tiny, light and zero power.
I have to find a use for them some day…
I have seen a couple designs, but the website for the one I tried appears to have disappeared. It uses a regular small (50mm?) speaker in the base of a resonator built using plastic water pipe. Unfortunately, I expect that the differences in pipe connector shapes from one manufacturer to the next has caused the resonant frequency to shift out of the available tuning range.
With a bit of reconstruction I think I can still get it to work.
It does provide audio filtering even using headphones connected in parallel with the resonant speaker, but that requires the speaker to be operational. More often, I’d rather not make more external noise then necessary, so something that can drive headphones alone seems like a better choice.
Hi Remy,
Of course, no CW filter will help you read CW much better than with a wider bandwidth if you aren’t well practiced in the art of receiving the code anyway. I’m unsure how experienced you are. One thing I did check though is if you are in my logbook - yes you are, but only twice in 2024 and both these contacts were in SSB. As I chase SOTA Activators on CW on more days than I don’t it seems that either I cannot copy your sigs or you haven’t been on CW much at all yet.
You are probably aware that the newer transceivers (Elecraft KX2/3, Icom 705 and possibly the Chinese variants) don’t require crystal filtering to operate. Most have audio filters and narrow variable filters that will still resolve CW signals down to 50 or 100 Hz using software defined digital processing.
73 and good luck,
Phil G4OBK
It’s too soon for April fool jokes Simon!
That’s because in those rigs there is no intermediate frequency stage, they are direct conversion receivers with phasing mixer to enable single sideband reception and conversely, single sideband transmission direct from baseband/audio frequencies. Audio frequency filtering, again done with DSP functions is the only option. I find the narrowest bandwidth of 50 hz very difficult to listen to on the kX3, but starting with a bandwidth of 500hz and narrowing it down as required works very well.
Upgrade to a more modern rig. Sell the cat if you have to. All the extra wires and boxes get to be annoying.
73
Ron
VK3AFW
As an activator I use a fancy modern rig equipped with all the filters. But I didn’t use CW on activations yet, I’m scared of the pileup. That’s why I start training with short chasing sessions from time to time, at home, with my 718.
Yes, the speaker is not an option. The wife is working online not so far away and I’m not sure she would be keen on “training her ears” 
.
Upgrading the rig is not in the equation yet. However, that’s an other point for the internal filter Vs the external audio box.
HI Remy,
That’s a really good idea, and you seem to be making plenty of contacts on CW, (I’ve looked at your Chaser log!) so I’m sure it won’t be long before you take the plunge and operate in that mode from a summit. Good luck!
73 Phil G4OBK
On my last activation, for the first time, I carried my very shiny bamatech paddle up to the summit. Just to see how she would handle the altitude and the fresh air from the mountains. I was not brave enough to plug it though. It’s coming for early this year I believe. Thanks for encouraging 
Get that key plugged in! Start at an easy comfortable speed - 10wpm even, chasers won’t care what the speed is, they just want the points (and possibly to encourage and grow another activator to give them more points!).
Don’t worry about mistakes, we all make them and once they’re sent, they’re pretty much forgotten about. Operating CW on a summit is challenging and I would hope that pretty much all of the chasers make allowances for that. There’s no heating, comfy chair, heavy desk key etc (unless you carry those those things up yourself!).
Good luck and please call me if you hear me.
73, Colin
I learn at around 18 wpm, when it’s too slow, I’m just getting lost. Sending is not a problem, when not stressed at home, I can send full QSO at 15-20 wpm without mistakes or so.
My receive on the other hand is not very reliable, I need extra farnsworth to “process” the letters in my head and write them on paper. If not written on paper, I just can’t send the call back. I start to hear prefixes (EA DL HB9 …) and other common codes (73, 559, TU …) as words and not letters by letters, though. It’s improving!
However, when I hear the pileup when chasing, it’s scary. Sometimes there is so many stations at the same that I only hear a continuous sound. Not a single letter. I’m afraid to not be able to pick up anything to start with. I will start a tuesday morning at 6AM to make sure there is no more than 4 chasers awake !
But it could help to justify the purchase of a new “quiet” radio 
“Darling, I thought about your idea of renovating the 40-year-old kitchen, but maybe you’d enjoy it more if I got myself a new rig instead. I promise it’s a quiet one!”
Q What’s the difference between a 40 yo kitchen and a 41 yo kitchen?
A An IC7300.
73
Ron
VK3AFW
Colin,
The NEQRP Nescaf is the one I built and yes, very impressive. Main thing I liked was no ringing.
In fact I bought 10 kits, they offered a slight discount, but the postage was higher than expected. I had 7 of them committed before placing the order. I never heard from anyone in the local qrp club who built one. The first one I built was for another op and after testing it, I sent it to him. The last one I built for my use but haven’t put it into the box yet.
73 Andrew VK1DA/VK2DA
