[Boatanchors] Switched capacitor filter - was Autek QF1 Filter pots
William Cromwell
wrcromwell at gmail.com
Sun Aug 14 09:25:12 EDT 2022
Hi Andree...
.....everybody,
I have been using a filter of this type kitted by the New England club.
They still have the info for it (last time I looked. The integrated
circuit has moved to surface mount format but was still available from
the major suppliers before covid. The New England design plays much
like Select-O-Ject from National Radio - something with vacuum tubes.
There are some differences. The main device can produce a notch or a
peak and a bandpass but the New England device is too simple to take
advantage of the notch function. More parts required. If you find one
(or a Select-O-Ject) for sale consider buying it. I have used mine with
a number of radios including regens from the 30s and 40s to good advantage.
73,
Bill KU8H
bark less - wag more
On 8/14/22 05:48, Andree Knott wrote:
> Dear List Members,
>
> this is a little bit of side topic, not really about how to repair the Autek filter but about another old type of filter: switchend capacitor filters.
>
> As mentioned filters like the QF1 have a tendency for ringing if set to a narrow bandwidth. This is a really annoying sound which somtimes prevents that one is able to concentrate to the signal.
>
> I used DSP filters for some time but they cause artefacts when set to narrow bandwidths. These audible artefacts have massive amplitudes. These filters also need a quite long time to calculate, which causes a time delay of up to half a second or so. This was a real disadvantage when I tried to compare the difference between input and signal output.
>
> I once came across the switched capacitor filters which were common in the 80s/90s and I can say, they are really the best choice for me. No ringing at narrow bandwidths, no artefacts, short delay time.
>
> I actually use a Smart Filter made by MSC and have had a SuperSCAF made by AFTRONICS as well. Both filters have selectable upper and lower cutoff frequency but the MSC is more comfortable, is switchable from CW to SSB and has an LED bargraph to show stopband and passband...
>
> Of course there are other filters of this type available and you can find the filter ICs still on eBay if you like to homebrew with this elder technology.
>
> So if you look for a sharp audio filter, you shold give these SC filters a try.
>
> 73 Andy DH5AK
>
> Holen Sie sich Outlook für Android<https://aka.ms/AAb9ysg>
> ________________________________
> From: boatanchors-bounces at mailman.qth.net <boatanchors-bounces at mailman.qth.net> on behalf of hwhall at compuserve.com <hwhall at compuserve.com>
> Sent: Sunday, August 14, 2022 12:59:10 AM
> To: boatanchors at mailman.qth.net <boatanchors at mailman.qth.net>
> Subject: Re: [Boatanchors] Autek QF1 Filter pots (long saga)
>
> If one half of the dual pot is still working, you can determine if it's linear or log by disconnecting & checking with an ohmmeter. Rotate the shaft to halfway between the stops & then see if from the wiper lug to either of the other lugs is 1/2 the total resistance. I suspect that since the pots aren't volume controls, they are linear.
> WayneWB4OGM
>
> -----Original Message-----
> From: Philip Atchley via Boatanchors <boatanchors at mailman.qth.net>
> To: Boatanchors at mailman <boatanchors at mailman.qth.net>
> Sent: Fri, Aug 12, 2022 9:42 pm
> Subject: [Boatanchors] Autek QF1 Filter pots (long saga)
>
> Hi All,
>
> It's been many years since I've posted here, think Duane F (and his
> frogs) may still have been alive then.
>
> Well, this may seem odd to all of you, but here goes, not exactly
> Boatanchors, but it is OLD. I do a LOT of NDB (longwave beacons) DXing,
> been at it over 25 years and Selectivity (IF & Audio) is 'everything' in
> digging out the weakest ones buried next to stronger ones, carriers
> etc. Now, my two primary (Yaesu) receivers both have excellent IF DSP
> (down to 50Hz) as well as audio peak filters for CW, very effective. I
> also use a homebrewed audio filter centered on 440Hz with a 6.5 Hz
> bandwidth, yes, 6.5 Hz! Really effective at the slow CW rates used by
> most NDBs. . .
>
> HOWEVER, I've long been a fan of the Autek audio filter, had a couple
> QF1A's back in the day. While they ring a bit at extremely narrow
> bandwidths, they are still quite effective, and I always regretted
> parting with my last one. The QF1A with it's extra notch filter is
> especially good, better than the plain-jane QF1.
>
> Well, I hadn't seen one for sale in a long time (didn't look especially
> hard though). Awhile back I found what I thought was a used QF1A for
> sale at HRO at the fair price of 49.95, (thought it was the 'A' model
> because their catalog number was QF1-ANA :-( It was described as
> "Scratched, one foot missing, working, switch needing cleaning". Shoot,
> that's all easy stuff, so I ordered it with a big smile on my face.
>
> Well, that's only half the story, it was NOT the "A" model, but the
> basic QF1. Oh well, you win a few, lose a few. Today after spray
> cleaning the filter switch and pots I tried it out. At first it seemed
> dead, then I realized that it partially works, but ONLY if the
> selectivity pot is turned clockwise. In checking I found that the front
> section of the dual pot is open. . .
>
> Both pots (selectivity & frequency) are 500 K dual section and I figured
> I'd replace both while I'm at it. The "broken" pot had obviously been
> replaced before as the solder job is sloppy. It also has a much longer
> flatted shaft than the frequency pot which has a round shaft. What I'm
> not sure of is the taper of the pots. Any QF1 experts out here?
> Antique Electronics has pots that seem like they'd be suitable, I only
> saw audio taper, no linear (maybe if I dig deeper). All at Mouser
> seemed to have knurled shafts.
>
> AS A SIDE NOTE. Autek has to have used what is the stiffest hookup wire
> ever made in this filter. I mean, it's really stiff! I've been at
> this electronics thing since around 1953 and I anticipate some possible
> problems safely connecting the wires to the new pots when I get them
> (some of the terminals have multiple wires).
>
> --
> <>< 73 From "The Beaconeer's Lair" ><>
> Specializing in DXing NDBs (Longwave Beacons)
> Phil, KO6BB, http://www.qsl.net/ko6bb/
>
> RADIOS:
> YAESU: FTDX-101MP Xceiver, Dual SDR Receivers (~2020)
> YAESU: FTDX-3000 Xceiver, DSP IF, 300Hz Roofing filter (~2019).
> Icom: IC-718 Xceiver, DSP.
> Portables: Eton Elite 750 (2), AKA Grundig Satelite 750 (2020)
> Sangean ATS-909X2 (2021), Tecsun PL-990 (2021)
> SDRs: Perseus SDR, SDRplay RSPdx
> ACC: MFJ-993B Auto Antenna Matcher.
> HOMEBREW 4 Port Antenna Multicoupler, Feeds 4 RX's.
> HOMEBREW Tunable LF-MF Pre-Amp.
> Ratzlaff 440Hz 6.5Hz BW CW Audio Filter.
> ANTENNAS: 88 foot Long Ladder-line fed dipole, ~35 feet AGL for MW/HF.
> Top Loaded Tee (Dipole fed as single element) ~35 Feet AGL.
> Butternut HF-6V 6 Band Vertical, ~12 Feet AGL for 75-10M
> Ratzlaff Active whip, 5 Foot Long, ~22 Feet AGL For LF/MW/HF.
> Wellbrook ALA1530LN Loop For LF/MW/HF at ~17 Feet AGL
> Diamond Discone ~35 feet AGL for Scanner.
> QTH: Merced, California, 37, 18, 37N 120, 30, 6W CM97rh
>
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