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Reviews For: W3NQN Passive Audio Filter

Category: Filters, Audio: (DSP and others)

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Review Summary For : W3NQN Passive Audio Filter
Reviews: 37MSRP: 70 USD $75 Cdn $90. overseas
Description:
Passive audio bandpass filter for CW Ed.W3NQN@comcast.net
Product is not in production
More Info: http://W3nqn.com
# last 180 days Avg. Rating last 180 days Total reviews Avg. overall rating
00374.9
VA3GUY Rating: 2015-04-16
EXCELLENT!!! Time Owned: 6 to 12 months.
I was searching for a passive CW audio filter when I came across Ed's site. As it turned out, he ran out of the older '5-inductor stack, three-resonator' components so he recently made some filters of a new type. These new filters use four potted inductors and are of a design by Jim Tonne (W4ENE) and feature arithmetic symmetry and improved group delay. This new design is intended to improve the quality of the received signal.

I was extremely fortunate to become a beta-tester for Ed so this report is based on quite a few tests in different situations. My testing comprised of using a mixture of 5 different headsets/headphones with various impedances. I did many comparisons of the DSP in my radio versus Ed's filter. I also tried using both at the same time. It should be noted that this filter has a fixed center frequency of 600 Hz (450 Hz available) with a 3-dB passband of about 200 Hz and is not adjustable.

The first thing I noticed about the filter was that there was no 'ringing' in the audio. When I set my DSP bandwidth on my radio down to 600 Hz and activate it, I get some ringing on the audio. Not so when using Ed's filter alone.

The second thing I noticed was the incredible amount of noise that had disappeared...including electrical noise, atmospheric noise and even some ignition type pulses. And once I 'zeroed' in on a CW station and activated the filter, I was amazed at the amount of rejection it produced. I was able to tune in the single station I desired and got rid of the majority, if not all, of the undesired signals. It seemed that with some weaker stations, when I flicked the filter on, there was almost an audio amplification effect. There isn't...it just sounds like it because there is no more QRM. There is a little of the typical filter hiss but very minimal. I tried using the DSP on my rig and the filter together and in most cases, there wasn't enough of a change to warrant using both. I found that I am extremely satisfied using Ed's filter on its own.

On many filters, when it is activated and/or deactivated, the volume of the audio can change and if the user is wearing headphones, it can hurt the ears. Ed has taken care of that problem by soldering a 33 ohm resistor across the switch to equalize the audio output so there is very little variance in volume level when the filter is activated or not. A nice touch!

The new filter is available (assembled) for $70 USD plus $15 USD Priority USPS. As mentioned above, the standard center frequencies are 450 Hz and 600 Hz and a custom center frequency is available for an extra $10 USD. Just email Ed and let him know. I can pretty well guarantee that you will NOT regret spending one cent...and you WILL be using it a lot!

Every CW operator should have one of these little wonders. Actually, it should be standard equipment in the shack!

Thank you very much Ed & Jim.

73,
Guy
VA3GUY
W0CCA Rating: 2015-03-24
Excellent Passive Filter Time Owned: 0 to 3 months.
It was a pleasure to work with Ed Wetherhold, W3NQN, on this filter. I requested a special lower center frequency as I have hearing loss that requires I listen to CW at 450-500 hz. Ed was very accommodating and built me a great filter. It is easy to operate and compared to a couple of more active type filters I have is much less fatiguing. I found I would leave it on in a QSO whereas the other filters you only use when you need them. The shoulders of the filter curve are softer so you can tune the band with the filter in (not quickly). I very much enjoy listening to the passive elements over active op amps and the like. I use the filter on all my receivers but in particular my R4B was quite noisy if the RF gain was advanced yet you needed that level of RF gain to make the AVC and S meter work as intended and get the benefits of the receiver circuitry. This filter totally removes the noise and leaves only the signal. Its great. If a signal is "pumping" your front end, it will still happen with this filter, but this filter is the most satisfying at the audio stage I have used.
W3KC Rating: 2015-01-27
New / Old Design - FB Time Owned: more than 12 months.
I installed the new 600 hz filter to complement my several years older 700 hz filter as I find I now often prefer listening to a lower tone. Having the ability to select either is very nice - and the performance of either filter is excellent. Ed is a gentleman and a pleasure to deal with.

73 Chas W3KC
K5SBR Rating: 2015-01-25
Terrific device Time Owned: 0 to 3 months.
Ed's latest passive filter is terrific. 200 hz. bandwidth centered on 600 hz. Knocks out all the DSP "artifacts", QRM, etc. and leaves nice clean CW. No ringing. No batteries required. It just works. Since the in/out is 8 ohms, it may be used with a speaker, too.
WC3N Rating: 2014-12-10
An excellent product! Time Owned: 0 to 3 months.
This review is for the passive LC 600-Hz CW filter. This filter was designed by Jim Tonne, W4ENE, to provide an Arithmetical Symmetry response for optimum reception of CW signals while using only four surplus potted toroidal inductors.

I wanted a better CW filtering option on my 2 older rigs, an Icom 751a and an Yaesu FT 990. The Yaesu FT 990 has DSP filtering but I was never happy with the hollow ringing sound it produces. I found it very fatiguing listening to this for any period of time. I had never heard of a passive CW filter before. But I must say it is very impressive. This filter works. It minimizes both the noise and distortion that I hear when using the DSP filter. It is much more enjoyable listening to CW using the passive filter and the fatigue factor is greatly reduced. I was using a Radio Sport headset which I can switch from stereo to mono. When using the filter you need to be in a mono headset.

On the Icom 751a it was equally impressive. I love switching into the CW mode and after switching on the passive filter just to get rid of the noise and start hearing clean, crisp CW signals. It really does reduce the fatigue factor. Anyone having an older radio with or without DSP and who loves CW should seriously consider this filter.

This unit comes with an internal 1K potentiometer to equalize the audio headset levels. If your receiver needs an adjustment just remove the cover and turn the pot shaft with the filter either in or out.

Ed, W3NQN, does the assembly work and I contacted him directly via email. It is a very well assembled product. From start to finish his service was top notch.
HS0ZFQ Rating: 2014-10-19
best purchase ever made Time Owned: 0 to 3 months.
I live in Thailand and ordered the kit from Ed
Wetherhold.I took it down to my radio man in Chiangrai with misgivings.After two weeks I was getting ready to take it to another guy when lo and behold he had finished it.I waited until the Worked All Germany contest this weekend and installed it between my headphones and my trusty Kenwood TS-830S which has never seen a filter.I found three stations close together and then turned the filter on. When I turned the dial on my rig it was like being in a tunnel with just one signal coming at me.I did not hear anybody on the sides. It was just plain incredible.Later that night I picked up a weak KP4CPC in Puerto Rico ( I had never heard Puerto Rico ) in ten years in Thailand.That did it. I needed to tell some people to quit wasting their money on expensive contraptions and just try the passive audio filter by Jim
Tonne and assembled by Ed Wetherhold. They won't be disappointed.
Richard
HS0ZFQ

WA2DFP Rating: 2014-10-05
Outstanding with CW Skimmer Time Owned: 0 to 3 months.
I like to use CW Skimmer software to monitor a 2 kHz pass band; but, I don't like to listen to all of the output. Placing the W3NQN filter between the transceiver and the speaker allows me to have it both ways - I see the whole 2 kHz on my computer screen, and hear only the 600 Hz note of the CW station I am copying. The output tone is clear, a real listening pleasure. I couldn't be more pleased with it. Other filters I tried, one active and one a simpler passive design (no input and output impedance transformers), did not produce the pure tones of this device.
W9FR Rating: 2014-09-08
Fantastic filter Time Owned: 0 to 3 months.
I recently evaluated and purchased a W3NQN 200 Hz audio bandpass filter using four potted inductors. This is the Jim Tonne, W4ENE, arithmetrical symmetry 600 Hz filter design.

The filter provides excellent rejection of band noise and adjacent signals. It dramatically improved the cw response of my IC756 pro 2 DSP based filtering. In all cases, it was not necessary to use the narrow DSP filter with its watery sound and ringing. I could leave the radio at 850 or 500Hz and switching in the passive filter would completely eliminate the background noise and only allow great clean reception of cw.
signals.

In the recent NA cw contest with strong signals on my non DSP IC737A. the passive filter would eliminate all of the signals that were present within the 500Hz crystal filter but outside of the 200 Hz audio filter bandwidth. Reception was fantastic with the background noise totally eliminated. Switching back and forth between the filter and radio clearly showed the elimination of signals that were within the 500 Hz crystal filter but were more than 200 Hz away.

In my non DSP based K2/100, the passive filter eliminated the hiss from the 700/400/200 filters when selected. It made the normally quiet K2/100 a real dream machine.

I also evaluated the filter at QRQ speeds at 70 wpm. While softening up the rise and fall times, it still allowed perfect copy without any ringing.

I highly recomment this filter and I should have purchased one of the Ed Wetherhold passive filters years ago.

Noel, W9FR
W0BGO Rating: 2014-07-29
Excellent filter Time Owned: 0 to 3 months.
A good CW filter is an essential tool to any amateur radio station. The standard 500-Hz CW filter found in most rigs doesn’t have the selectivity to operate under difficult conditions when DX’ing amidst DX pileups or Field Day where the CW portion of the band can be wall to wall signals, a bandwidth closer to 250 Hz is required.

A nice complement to the standard 500-Hz IF filter is an outboard audio filter. Nearly all available designs are active, using IC’s, transistors and DC power. These introduce noise or hiss and often distortion of some type to a degree. A new CW filter designed by Jim Tonne, W4ENE is in a different class by itself as it is passive. No power supply, or IC’s are required. Just plug your headphones or earbuds in and go. Since it is passive there is no added noise or hiss.

I used the Tonne passive 4-resonator CW filter along with W3NQN Ed Wetherhold’s passive 5-resonator CW filter featured in QST, CQ, Rad Com and many issues of the ARRL Handbook during the 2014 Field Day. I have always considered W3NQN’s filter the “gold standard” in passive designs. This is a superb filter that was available for 30 years but unfortunately is unavailable. The source of surplus toroids from old analog telephone equipment has dried up. I was glad to hear Jim Tonne’s design also uses surplus telephone toroids (a different value) but in a novel new approach called “arithmetical symmetry attenuation” The end result is excellent.

Both filters are centered at 600 Hz and both exhibit a high degree of sideband attenuation. The measured insertion loss and measured -6 dB bandwidth of 265 Hz were identical. There was nearly no difference between the two filters in the high frequency response where the measured attenuation was 40 to 70 dB between 1 kHz and 1.5 kHz. However, the low frequency response does show a difference where W4ENE Jim Tonne’s filter attenuation measured 18 to 35 dB between 350 Hz to 200 Hz and W3NQN’s filter attenuation measured 35 to 70 dB between the same frequencies. The difference was noticeable during Field Day where the interfering signal was a couple hundred Hz lower. Switching to W3NQN’s filter made a noticeable difference.

I have owned several active CW filters over the years using both Hi-Q opamp circuitry and SCAF (Switched Capacitor Audio Filter) designs. One thing I have noticed, is that when they are adjusted to the same bandwidth or Hi-Q setting as the passive filters they often exhibit a ringing/hollow sound when listening to the background noise. The passive filters are cleaner as the background noise sounds more natural. The passive filters in general exhibit the best ultimate attenuation often exceeding 70 dB. A popular SCAF CW filter currently being sold has an ultimate rejection of just over 50 dB when measured at the 200-Hz and 1.5-kHz points. When comparing the sound quality of a passive filter to a 250 Hz crystal filter, the passive filter doesn’t exhibit the harshness of sound. There is less listening fatigue using a passive filter.

I really enjoy using these passive filters. I found it absolutely essential to use a filter like Jim’s during Field Day. The 20m CW band was mayhem and the 265 Hz bandwidth allowed QSO copy that otherwise would have been impossible.
If you enjoy good CW audio and need an extra boost to capture that elusive signal, you might consider a passive CW filter like W4ENE Jim Tonne’s. You won’t be disappointed!

W3NQN will offer the filter components for this Passive 600-Hz CW Filter in the form of two options:
a. Kit Form. The four matched potted inductors will include the schematic and pictorial diagrams, a Bill of Materials giving a distributor stock number. Cost is $15 postpaid for the USA and $20 for Canada and Europe.
b. Assembled filter with a 600-Hz center frequency. $70 postpaid for the USA.
c. For details please send an email to: Ed Wetherhold ed.w3nqn@comcast.net
VE7HS Rating: 2014-07-24
Works very well! Time Owned: 0 to 3 months.
Some time ago, Ed sent us a passive 600 Hz audio CW filter that we evaluated - first at the VE7NA Club Station, where we tried it with three different transceivers, including a Kenwood TS590, a Yaesu FT897D, and a Yaesu FT101Z, and then during our Field Day operation. All those who used the filter have been very pleased - sharp bandwidth, an noticeable lack of noise and hiss, just signals popping out of the noise. The lack of hiss and noise makes it quite comfortable to copy even for long periods of time.

The 600-Hz center frequency filter consists of four potted inductors having an arithmetically symmetrical response in a design by Jim Tonne, W4ENE. This attenuation response is intended to optimize the clarity of CW signals because of its superior envelope delay as compared to the more common Cauer and Chebyshev responses. Bandwidth of the filter is 200 Hz.

When we first began to use the filter, all that was required to equalize the sound level whether the filter was in or out was a small adjustment of a variable resistor. The quality of sound was also impressive, especially on strong signals, with no distortion noticed.

And because it's a passive filter, we didn't need to find a power supply, either - just plug it into the audio jack and turn it on, with the headphones plugged into the filter.

If you want your own filter, for $15 US, Ed will mail four matched potted inductors having the two internal toroidal windings wired in series-aiding to provide an inductance of 70 to 80 mH, including a pictorial diagram showing the filter wiring with a listing of the capacitor values, a schematic diagram of the filter, and a bill of materials with recommended distributors and stock numbers so any interested user can conveniently obtain the necessary parts; or for $80 US, Ed will provide, postpaid, a fully assembled and tested 600-Hz center-frequency filter to any US or Canadian hams interested  in obtaining an assembled filter. The filter is intended for a mono-two-wire headset.

After Field Day, I put the filter in my own shack, where I got similar results with my old TS-820S which came with a 500Hz CW filter. Filter out, noise and signals, filter in, just signals. I'm very pleased with this filter, and it will be a mainstay in my radio room for years to come.

Bob Smits, VE7HS


----------------------
Earlier 5-star review posted by VE7HS on 2014-07-08

Some time ago, Ed sent us a passive audio CW filter that we evaluated - first at the VE7NA Club Station, where we tried it with three different transceivers, including a Kenwood TS590, a Yaesu FT897D, and a Yaesu FT101Z, and then during our Field Day operation.

All those who used the filter have been very pleased - sharp bandwidth, an noticeable lack of noise and hiss, just signals popping out of the noise. The lack of hiss and noise makes it quite comfortable to copy even for long periods of time.

When we first began to use the filter, all that was required to equalize the sound level whether the filter was in or out was a small adjustment of a variable resistor.

The quality of sound was also impressive, especially on strong signals, with no distortion noticed.

And because it's a passive filter, we didn't need to find a power supply, either - just plug it into the audio jack and turn it on, with the headphones plugged into the filter.

In the tradition of ham radio, you get this as a kit, with all the parts including the case. No running around trying to find all the bits, it's all there.

After Field Day, I put the filter in my own shack, where I got similar results with my old TS-820S which came with a 500Hz CW filter. Filter out, noise and signals, filter in, just signals.

I'm very pleased with this filter, and it will be a mainstay in my radio room for years to come.

Bob Smits, VE7HS