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Reviews Categories | Filters, Audio: (DSP and others) | W3NQN Passive Audio Filter Help

Reviews Summary for W3NQN Passive Audio Filter
Reviews: 28 Average rating: 4.9/5 MSRP: $70 USD $75 Cdn $90. overseas
Description: Passive audio bandpass filter, center frequency 800Hz eMail:
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VE7HS Rating: 5/5 Jul 8, 2014 15:59 Send this review to a friend
Works very well!  Time owned: 0 to 3 months
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
KA5QQA Rating: 5/5 May 3, 2014 18:56 Send this review to a friend
An effective audio filter with no ringing!  Time owned: 3 to 6 months

I have been pleased to have the opportunity to evaluate a new cw filter designed by Jim Tonne and produced by W3NQN. I have been searching for additional filtering for my Elecraft K2 including it’s useful KAF2 active audio filter. My major difficulty has been filter ringing and QRN that gives the crystal filter fits when trying to copy “weak” or “just in the noise” cw signals with or without QSB. Also the hiss of the AF1 and the Ringing of the AF2 filter in the K2 audio filter hinders some weak signal work.

My main antenna is a full sized 40 meter delta loop supported by a 38ft. Maxgain fiberglass mast, fed with 20 feet of ladder line to a MFJ 998b auto tuner housed in a weather sealed box near the feed point of the loop. I live in the Houston metro area with its many noise sources. I feel this is a relatively quiet choice and works well on 10-40m and will just work on 160-80m. Because of some unresolved noise sources at my operating position at our family computer desk, I have successfully reduced some of the noise at times by setting up my rigs near the tuner in the back yard, weather permitting.

My main pursuits are QRP DX, QFox hunts, SOTA chasing, and portable operating such as Field day and QRP to the field events and contests.

The filter arrived well protected in a “beta” enclosure labeled as : A 4 inductor, 7 capacitor passive cw filter using 4 potted inductors, 7 capacitors. The only control consists of a single toggle switch for bypass and filter selection, a headphone jack, and a mono audio jack to bring the rigs Ext. speaker or headphone output to the filter. No power required.

After the simple connections were made to my K2, I mainly used a K-251/U, Astrocom Army communication headset and occasionally my Scullcandy cellphone earbud that I already alternately use with the rig and use as a comparison and control with the filter out of line.

First impression with minimal QRN is the passive filter has a sweet, sound that doesn’t cause the fatigue that, at least my KAF2 generates over time, I think due to its hiss and ringing. None of my filters nor this passive filter deals well alone with high QRN in conjunction with a signal at the noise level. Luckily the KNB2 noise blanker does deal with many of my static issues. But this filter does add another layer of filtering that helps my crystal filters separate weak cw signals from the QRN/static. Also this passive filter sounds great with stronger signals, narrowing the bandwidth without ringing for signal reception with a great tone and no hiss! Now this is an audio filter so, strong adjacent signals can splatter, requiring the use of my 700, 400, and 200hz crystal filters in the K2. And the great tone and lack of hiss help the crystal filter in the K2 sound even better.

So… no single filter is a solution to every situation, but this is a great tool used alone or in combination with other filters in many common situations on our hf bands. I also used the filter with my other rigs including an Icom 751a, Elecraft KX1 and K1 with similar results in each. I even tried it on PSK with some very positive results keeping the signal within the bandwidth of my waterfall. Would really enjoy trying one with a center of 1000hz for digital and a wider version for SSB. Bet they would be real winners too. Hint hint…

W4OP Rating: 5/5 Dec 31, 2012 13:04 Send this review to a friend
Fantastic CW Filter  Time owned: 3 to 6 months
I just recently installed this filter in a station accessory I built for my Hallicrafters FPM-300 MK II transceiver. Totally different sound than SCAF or op-amp active filters- and perhaps the best part is that you do not need to be concerned with keeping the input AF level within a certain range in order to not overload active devices.
Exceeds my expectations and Ed's customer service is excellent

Dale W4OP
KI0Z Rating: 5/5 Apr 11, 2012 18:36 Send this review to a friend
AWSOME  Time owned: 0 to 3 months
ANYTHING THAT CAN HELP THE TS-590 & IC-7800 is worth looking at!! this is an amazing design .. I have had a lot of filters but this Active filter Is a big help WOW ........!!!!!!oN THE ts-590 NR-2 WHEN LISTENING TO cw YOU GET THE POT HOLES OF REMOVED BAND NOISE SPACES AND THE cw SIGNAL. turn on the W3NQN filter and it's just CW signals only !!! even on wide filter settings of the xcvr it has a lot of selectivity. just set it up for stereo plug and jack.Don't short out 1/2 of the signal out of the xcvr with a mono plug!!tye both hot of plug to input wire and have full output at filter.same as at xcvr.use the filter on the IC-7800 snd hesr both rcvrs in both ears at once with stereo setup. . GL 73 DX Dave KI0Z..
W8FA Rating: 5/5 Mar 7, 2012 16:21 Send this review to a friend
Save your ears, get this filter.  Time owned: more than 12 months
I can't say enough about this simple PASSIVE audio filter for CW. I use it every day. There is no ringing, echo, hiss or roar. It is so much more pleasant to listen to the band background noise using this filter compared to others I've used, which are either built into the rig (crystal or mechanical), DSP, or, are an outboard accessory, for which I have a box full, with some costing $500. THIS FILTER DOES NOT ADD DISTORTION TO THE RECEIVED AUDIO like typical active filters, DSP, etc. It also makes it easier to dig weak signals out of the noise level. The kit was easy to build. I did add extra output connections and switches on the filter box in order to direct the output audio to other pieces of equipment, speakers, and multiple headphones. The only problem I had was with two inductor wires broken at their solder connection point. I quickly found this problem after checking with an ohmmeter, but could have seen the bad connection if I had opened my eyes. You do not have to be a homebuilder to build this filter. It's simple point-to-point soldering at about two dozen points. There is even step-by-step pictures of construction on the website which you can click-on and enlarge. If you operate CW, save your ears and get this filter. Does it work miracles? No. The band noise is still there, although at a reduced level. But most important, the noise is less tiring. And without distortion. I plan on using this filter for life. This is one of the few accessories I've used in the last 40+ years that really works. Considering what a simple passive filter like this costs, I can't figure out why the big transceiver manufacturers don't build these into their multi-thousand dollar rigs. Oh wait, maybe I can figure that out.
G3LGR Rating: 5/5 Mar 7, 2012 07:51 Send this review to a friend
Excellent non rringing filter  Time owned: 3 to 6 months
Recently purchased a 600Hz version of the filter from Ed to carry out some very low signal to noise tests.
before starting the tests I tried the filter on my IC 706 and FT 897. The filter has been a pleasure to use, no ringing, just an absence of noise and reduction of nearby signals. I've not bothered using my 599ZX on the HF and found that the filter when combined with the BHI DSP unit at a low setting has provided a very nice relaxing way of sorting out weak Cw stations, especially on my favourite band, 40 metres.
Ed produces the kits at various frequencies from 500 Hz upwards
N7AG Rating: 5/5 Apr 5, 2011 00:31 Send this review to a friend
THE CW FILTER  Time owned: more than 12 months
If I could have but one cw filter, this is it. His website is most useful for construction. Filter is not tiring to listen to. Have tried numerous DSP, low-pass filters.
F6DFZ Rating: 5/5 Mar 3, 2011 10:18 Send this review to a friend
Impressive  Time owned: 0 to 3 months
I have just finished my W3NQN CW filter and put it in service with my Collins 51S1 receiver. The improvement is absolutly impressive. This filter increases the selectivity (generaly 51S1 comes with a 800 Hz Bulova crystal filter), improves the sound of CW signals, reducing the distorsion introduced at the attack by the AGC, greatly reduces the back ground noise, and supresses the switching transcient when transmitting with the Collins KWM2A. Of course, the 1750 Hz from the KWM2A side tone is filtered out. I solved this question with the injection of the side tone from my keyer in the RCA ad hoc plug on the back of the 51S1.
A very worthwill addition, even if you own a modern rig.
WB6SSW Rating: 5/5 Nov 29, 2009 16:50 Send this review to a friend
Amazing Performance  Time owned: 0 to 3 months
I've got all homebrew station. The receiver is an HBR-16, a design from the late 50's with no selectivity other than what it can muster from dual conversion and two stages of IF. No crystal or mechanical filters and, of course, no DSP. Ed's (W3NQN) filter turned a nice project radio into a great CW receiver.

The filter comes in a kit of parts, a surplus telco five inductor toroid stack, two additional 88 mH inductors, two small audio output transformers, a bag of capacitors and a bunch of hardware (box, switches, etc.) Ed takes the time to mark the capacitors with their appropriate schematic designation, C1, C2, etc.

Assembly is fairly straightforward. Ed suggests using silicon sealant to mount the capacitors and toroids to the telephone inductor stack. I used a hot melt glue gun which worked just fine and I didn't have to wait to the glue to dry.

I am sure that most buyers will take the outboard approach and use the box, plug and jack to house the filter. However, in my case this was going to be a integral part of my homebrew receiver. So the hardest part of the project was finding room for the filter and the two audio transformers, because this filter is BIG. The assembled filter without the audio transformers is about 5" long 2" wide and 2.5" tall, and weighs just about one pound.

After making room in the receiver, mounting the components and wiring up a front panel "wide/narrow" switch, it was time to test it out. Wow. What a difference. About a 300 Hz passband at the -6 dB point at 450 Hz at-20 dB (Ed reports 325 Hz and 460 Hz and my measurements were a bit better than that).

Best of all, as has been reported in other reviews of this filter, no ringing. A real pleasure to listen to. And, it's kind of spooky seeing the S Meter jump around from signals outside of the filter passband, and not hearing a thing from the speaker!

If you've got a "wide" receiver and want to use it on CW, this may be just the ticket.
K3ANG Rating: 5/5 Apr 24, 2009 21:35 Send this review to a friend
Worked well when I had it  Time owned: more than 12 months
I got one of these kits from W3NQN back in the 1980's. A fellow ham had one, let me try it out, and I just had to get one. Worked very well. I lost it back in 1995 during a move to my current qth.

To KB9WIS: Go to QRZ.COM to get W3NQN's snail mail address. That's the best way to get HIS KIT. No one sells them already made. You have to build it.

de K3ANG
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