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Reviews Categories | Filters, Audio: (DSP and others) | Elecraft AF1 Active Filter with Audio Amplifier Help

Reviews Summary for Elecraft AF1 Active Filter with Audio Amplifier
Elecraft AF1 Active Filter with Audio Amplifier Reviews: 6 Average rating: 5.0/5 MSRP: $$59.95
Description: The Elecraft AF1 is a versatile audio filter that can be used with any receiver or
transceiver. It can improve intelligibility of CW, phone, or data signals, and is
especially well suited to radios that have inadequate I.F. or audio filtering. The
AF1 uses straightforward analog circuitry and no surface-mount components, so
itís an ideal project for first-time kit builders.

A rotary switch on the unit allows you to select a low-pass characteristic with
adjustable upper frequency roll-off, or a narrow bandpass characteristic. The
bandpass filter offers two levels of selectivity, and its center frequency may be
tuned from about 350 Hz to about 950 Hz. The low-pass filter is active during
bandpass operation, allowing you to further control the upper frequency
response. The output amplifier drives low impedance phones or a small
loudspeaker. Power can be supplied via either an on-board 9-V battery or an
external supply. An LED indicates power on/off status.
Product is in production.
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You can write your own review of the Elecraft AF1 Active Filter with Audio Amplifier.

K4ALE Rating: 5/5 Sep 6, 2015 18:07 Send this review to a friend
Very fine for older rigs  Time owned: more than 12 months
I built this easy kit about two years ago to use with a variety of older radios, ranging from an HRO-50 to a very nice TS-830 whose variable filter is way out of alignment (and a bear to fix). It is simply marvelous. Although it helps a lot with SSB, its main value is with CW. All those distracting beeps that wear you out, unless you think in Morse Code, are pushed away, often entirely. The skirts are plenty sharp, and rarely do you have to 'head filter.' I believe mine is the 200 Hz width advertised. I have gotten a little spoiled by my KX3, but this makes so much positive difference with my older receivers that it follows me wherever I migrate around the toys in my shack.

I use mine in front of a 'Son of Zero Beat' kit, which provides a companion visual clue to where my narrow bandpass is relative to a target CW signal. I simply tune to maximum volume and the green LED marker on the SoZB. Once properly set up, you will be transmitting in the center on the filtered signal and very close to the other station's transmit frequency.

However, the AF1 also functions in much the same way by itself. When peaked on your own sidetone, you will be pretty well dead beat on the other signal anyway. This is a huge help if you are running a separate transmitter and receiver because it enables you zero beat the transmitter very quickly.

Anyone using any fine old receiver will be very happy with this superb filter. It works equally well with other simple QRP receivers and is easy to build.

The only other filter experience I have is with some early DSPs. This is a Great Leap Forward.
W8KRR Rating: 5/5 Sep 13, 2014 11:42 Send this review to a friend
Great little AF   Time owned: more than 12 months
This is a nice little filter. I use it in conjunction with my Elecraft KX1 for even better audio. Nice one evening build, and a useful addition. My shack is small, consisting only of the KX1. This kit not only provides nice audio filtering, but also nice audio gain to allow running the KX1 through a speaker rather than headphones.
KA5KXW Rating: 5/5 Sep 2, 2013 19:48 Send this review to a friend
Well Done Little Filter  Time owned: 0 to 3 months
I scratch built an AF1 since I had all the parts laying around. I won't do that again as I've built other Elecraft products and their boards are so well done. I probably invested 10X the time in completing it from scratch.
The Low Pass Filter is a little light for use with my Kenwood as the top end is heavily rolled off anyway, but the bandpass filter is very useful, clean and just tight enough for any use that I could ever have. The low pass filter would likely be a lot more useful with DC receivers.
I really, really like this filter.
AE5J Rating: 5/5 Nov 14, 2012 19:17 Send this review to a friend
Worthwhile Gear  Time owned: 0 to 3 months been using the little AF-1 for a week or so now and it simply works as advertised. I needed a little extra filtering for my FT-817 and 857D when doing field work and the AF-1 fit the bill perfectly. Fun to build in only an evening although my old eyes are not as good at reading tiny resistors as they used to be.

I mounted it in one of W8FGU's excellent enclosures. A great product and well worth the money.

I am an audio filter user from way back having started with an Autek QF-1 and moved to a QF-1A. The AF-1 is way more useful for my purposes because it can be powered by a 9V or 12V battery. The Auteks requires AC. One note to remember. The AF-1 has almost no power line conditioning, so unless your power supply is extremely clean, you'll get some hum.

Other than that little issue, a great product that is really useful for CW.
AC7AC Rating: 5/5 Dec 16, 2010 10:49 Send this review to a friend
Great addition to many receivers.  Time owned: more than 12 months
I dug out my AF1 after reading about the popular Audio Peaking Filter (APF) DSP addition to many high-end transceivers. Elecraft recently included APF in their K3 transceiver which greatly pleased many people who owned other rigs with APF. The "beauty" of APF is that it offers very narrow bandpass with soft skirts that make CW signals seem to "pop out" of the background, rendering some signals unreadable without out it easy copy. I found my AF1 analog filter provided the same sort of effect and, comparing it with DSP APF in the K3, can find no audible difference between them. The effect is, indeed, amazing on the right signals. So here's a way to add the latest digital effect in high-end transceivers to any receiver at a nominal price.

The unit comes without an enclosure. For those wanting a nice case for it, W8FGU has durable lexan enclosures available at a nominal price:
N6NUL Rating: 5/5 Dec 16, 2010 10:24 Send this review to a friend
Helpful with marginal signals  Time owned: 0 to 3 months
While reading a thread about the new APF feature for the Elecraft K3 and how amazing it is, Ron AC7AC mentioned that the AF1 could provide a similar feature for other radios, including my Elecraft K1 and borrowed TS-830s. So, I thought I would give it a try.

As with other Elecraft mini-modules, the AF1 is a fun evening build. There are no surface mount components and nothing particularly tricky about the other. My only hick-ups were finding one of the lock washers lodged in the selector switch and a slight error in the built errata, which I reported to Elecraft. Also like other mini-modules, there is no case, but nice cases are available from other hams online.

In use, the AF1 sits nicely on top of my K1 and the provided rubber feet are enough to keep it from moving while adjusting the knobs, including the relatively stiff switch that turns the board on and selects between the low-pass, band pass 1, and band pass 2 filters.

Another nice feature I was not expecting is that when the unit is not engaged (off), audio is still passed through to the headphones. This means you do not need to have it turned on all the time and can engage it only when necessary. This will save on battery power when i operate mobile.

During the ARRL 10m contest I made several contacts with stations that were very faint and I could not copy 100% without having the band pass filter engaged. While not magic, the intelligibility of the signal improved enough to permit the QSO, and that is the point of the product.

This week, I used another tip from Don W3FPR on the Elecraft mail list and used SignalScope on my iPod touch to tune the band pass filter to my side tone pitch. Some listening during the NAQCC sprint showed improved selectivity of the filter, at least to my ears.

I give the product a 5 because it was fun to build and I believe it helped me made QSOs I would not have made without it.

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