[AMRadio] Re: AMRadio digest, Vol 4 #199 - 3 msgs
patrick jankowiak
eccm at swbell.net
Sun Oct 19 01:19:28 EDT 2003
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> Today's Topics:
>
> 1. Re: FW: Homebrew receiver (David Knepper)
> 2. RE: FW: Homebrew receiver (Brett Gazdzinski)
> 3. Re: FW: Homebrew receiver (David Knepper)
>
> --__--__--
>
> Message: 1
> From: "David Knepper" <cra at floodcity.net>
> To: <amradio at mailman.qth.net>
> Subject: Re: [AMRadio] FW: Homebrew receiver
> Date: Fri, 17 Oct 2003 08:21:24 -0400
> Reply-To: amradio at mailman.qth.net
>
> Very fine, Brett. In all the receivers that I have at the Collins Radio
> Center, I like the NC-303, the best for AM
>
> Dave, W3ST
> Secretary to the Collins Radio Association
> Publisher of the Collins Journal
> www.collinsra.com
> ----- Original Message -----
> From: "Brett Gazdzinski" <brett.gazdzinski at mci.com>
> To: <amradio at mailman.qth.net>
> Sent: Thursday, October 16, 2003 8:50 AM
> Subject: RE: [AMRadio] FW: Homebrew receiver
>
> > Dave,
> > Many receivers did just that.
> > I don't remember if the NC300/303 used the rf amp on the low bands
> > or not.
> > The NC300/303 was one of the best AM receivers I ever had.
> > I think it needed better audio stages, but I always used a detector
> > output.
> > Frequency resolution and stability were very good, bandwidth choices
> > were good, although I don't remember how sharp the filters were.
> >
> > The looks of the thing were quite Art Deco, and did not turn
> > everyone on, but they are very good receivers in my book.
> > Hard to mount one in a rack though, with the rounded corners.
> >
> > I am not sure how much the RF amp adds to the noise level.
> > A well designed rf amp section can actually reduce noise levels.
> > Noise mostly comes from mixers, and overall tube counts.
> > All mixers add some noise, some designs are much better than others,
> > and the more there are, the more noise you get.
> >
> > I used single conversion, with a quiet mixer setup, and
> > used two tuned circuits of very high Q in the input,
> > along with resonant dipole antennas for 80 and 40 meters,
> > so I don't get any images or other problems, as signals
> > out of band are attenuated very much before making it to
> > the mixer. This is not always the case in the general receiver
> > setup, as many bands are covered, low Q broad band coils are used,
> > and who knows what antenna will be used.
> >
> > As far as the NC303/300 goes, if you can get past the style,
> > the only big improvement to be done would be the audio output
> > (if used), and maybe the addition of a KIWI filter module.
> > These are quite like mechanical filters, very sharp.
> > One of those would be very easy to add, without hacking
> > up the receiver.
> >
> > Brett
> > N2DTS
> >
> >
> > > -----Original Message-----
> > > From: amradio-admin at mailman.qth.net
> > > [mailto:amradio-admin at mailman.qth.net]On Behalf Of David Knepper
> > > Sent: Thursday, October 16, 2003 4:31 AM
> > > To: amradio at mailman.qth.net
> > > Subject: Re: [AMRadio] FW: Homebrew receiver
> > >
> > >
> > > Brett and others, I wonder if we could somewhat emulate the
> > > same results as
> > > you had by eliminating the RF stage from let us say a NC-300
> > > receiver and go
> > > directly into the mixer stage.
> > >
> > > I am sure that this has been tried before for operation on 160 and 80
> > > meters.
> > >
> > > Just a thought that is not so original.
> > >
> > > Thank you.
> > >
> > > Dave, W3ST
> > > Secretary to the Collins Radio Association
> > > Publisher of the Collins Journal
> > > www.collinsra.com
> > > ----- Original Message -----
> > > From: Brett Gazdzinski <brett.gazdzinski at mci.com>
> > > To: <amradio at mailman.qth.net>
> > > Sent: Wednesday, October 15, 2003 8:46 PM
> > > Subject: [AMRadio] FW: Homebrew receiver
> > >
> > >
> > > > This is what I plan on sending to Electric Radio, along with
> > > > pictures.
> > > > What do you guys think?
> > > >
> > > > Brett
> > > > N2DTS
> > > >
> > > >
> > > >
> > > > I wanted a complete home brew station, and since I have
> > > > a homebrew pair of 813,s, modulated by one of two modulator
> > > > decks, push pull parallel 100TH,s, or a pair of 4sc250b,s,
> > > > and a classic push pull rig with link coupling, using 812,s
> > > > modulated by
> > > > a pair of 811,s, only a receiver was needed.
> > > > At first, I thought I would build something simple that worked
> > > > just well enough to be able to copy AM under good conditions, just
> > > > so I could say I had a home brew station.
> > > > But I wanted something a little better than the regen receiver
> > > > type of radio, maybe a simple superhetrodyne.
> > > > I did loads of research, looked in Bill Orr, and all my old
> > > > ARRL handbooks, looking for simple receivers.
> > > > All the circuits had some sort of problem, complex tapped coils,
> > > > hard to get parts, poor designs, etc.
> > > > I also looked at the diagrams for things like my Gonset
> > > G76, the Scott
> > > > model SLRM I have, the Hallicrafters sx17, and the R390.
> > > >
> > > > I decided to base the receiver on the Scott SLRM, since it works
> > > > very well, has good fidelity, uses 8 pin tubes and a 455Khz IF.
> > > > I ran into problems though, as the Scott was built to
> > > reduce emissions
> > > > out the antenna, with loads of shielding and an rf amp with
> > > > tuned circuits.
> > > >
> > > > I accumulated parts, and started construction with the basic layout
> > > > of two tuned circuits on the antenna input, an RF amp, a separate
> > > > local oscillator and mixer, two stages of IF amplification, hifi
> > > > detector, s meter circuit, agc circuit, and power supply.
> > > >
> > > > Since it was to be experimental, I used octal sockets for
> > > everything,
> > > > the antenna coils, the local oscillator coils, and the IF
> > > > transformers.
> > > > The receiver started out with plug in coils to change bands.
> > > >
> > > > I laid out all the parts, leaving room between things to allow
> > > > room for experimentation, and mounted the basic parts.
> > > >
> > > > I tried various circuits for the local oscillator, using coils
> > > > wound on ceramic forms, B+W coil stock, and slug tuned ceramic
> > > > coil forms.
> > > > This step would have been very difficult without the aid of a
> > > > very nice spectrum analyzer I have through work. It allowed me
> > > > to look at the frequency output, harmonics, hash, drift,
> > > > frequency range, amplitude, all at the same time.
> > > >
> > > > At first, I went with plug in coils in the local oscillator,
> > > > used the rf amp, using the spectrum analyzer to peak things
> > > > and check gain. The mixer was easy, then to a filter.
> > > > I planed on using a mechanical filter, but they are
> > > > expensive, and a little tricky to put in the circuit.
> > > > I found a company on the web, kiwi, who makes various filters, and
> > > > went with one that has an op amp input, three filters of slightly
> > > > different center frequencies (sets bandwidth) and an op amp output,
> > > > and runs off 10 to 30 volts dc.
> > > > There is no loss through the filter, and its quite similar
> > > in results
> > > > to a mechanical filter. I used a 5.5kc model.
> > > > It mounts on Velcro, and has pig tail shielded wires to hook up
> > > > to the IF system.
> > > > This filter is easy to add to any receiver using 455 KHz as an IF,
> > > > and really works fantastic.
> > > >
> > > > I copied the IF system out of the Scott, and used a hifi detector
> > > > on one of the AM web pages.
> > > > It took some experimentation to get the agc takeoff and IF gain
> > > > control systems working well, then I added the S meter
> > > circuit I stole
> > > > out of the Bill Orr handbook using a 6SN7.
> > > >
> > > > Taking the receiver for a test drive revealed problems.
> > > > Startup drift was excessive, muting the receiver seemed impossible,
> > > > the RF amp caused all sorts of problems, and the if amps were
> > > > unstable.
> > > >
> > > > As a test, I hooked the antenna up to the mixer input, and bypassed
> > > > the rf amp, and had very good results, so I removed the rf amp
> > > > completely, and went with two tuned circuits then into the mixer.
> > > > Some experimentation with the antenna link on the input
> > > coil boosted
> > > > gain quite a bit.
> > > > I ordered a selection of NPO caps, and did weeks of experimentation
> > > > on the local oscillator stability, changing components,
> > > > design, putting the coil in a metal plug in can to shield it, and
> > > > got the stability much better, but still have startup drift for
> > > > the first 5 minutes.
> > > >
> > > > Careful shielding and reducing the gain of the IF
> > > eliminated the odd
> > > > oscillations I got at times, and the receiver was working
> > > quite well.
> > > >
> > > > I did not like the tuning dials I had, marking the
> > > frequency was hard
> > > > with the drift, and I have a real problem marking the frequency
> > > > so it looks nice on the dial.
> > > > I needed something better, and found the almost all digital
> > > > electronics digital frequency readouts, basically a
> > > frequency counter
> > > > with a selectable frequency offset.
> > > > You program the thing to offset the IF frequency, in my
> > > case, 455Khz
> > > > lower, and all you need to do is get the pickup close to the
> > > > local oscillator tube, and the display reads the exact
> > > > receive frequency down to 1000 Hz.
> > > > I used their backlit display, which looks nice, and a real accurate
> > > > frequency readout is very nice to have.
> > > >
> > > > The performance of the receiver was astounding!
> > > > With the transmitting antenna used, sensitivity was very
> > > > good, fidelity was great, I use a marantz amp on all the receivers
> > > > in the shack, to a big three way speaker, and the homebrew sounds
> > > > the best, because of the low distortion fi fi detector I guess.
> > > > The biggest surprise is the noise level.
> > > > Since the tube count is low, and the mixer design is a quiet one,
> > > > the receiver is incredibly quiet.
> > > > Its MUCH quieter than anything else I have, or have ever had.
> > > > Forget the modern rigs, the IC chips just can not run quiet, and
> > > > there are so many of them in modern rigs that the noise
> > > and distortion
> > > > in any modern rig I ever used is way high.
> > > > Comparison to my very well working r390a was dramatic, I
> > > could CLEARLY
> > > > hear signals that were well under the hash level of the r390a,
> > > > the signals were unreadable on the R390a, but very good
> > > > comfortable copy on the homebrew receiver.
> > > >
> > > > After the results I got out of the homebrew, the plan changed from
> > > > something I could use sometimes, just to have a complete home
> > > > brew station, to the receiver of choice.
> > > > This caused problems.
> > > > I had the receiver mounted in a rack cabinet, and had to run around
> > > > back to change the plug in coils, a real pain in the butt
> > > over time.
> > > > So out came the receiver, and a new front panel and band switching
> > > > was added, along with 160 meters.
> > > > Tuning was changed to a system using TWO back to back vernier
> > > > drives, the tuning range was changed to cover only part of the
> > > > ham bands, giving very nice slow tuning range.
> > > > A bfo was needed for zero beating AM signals, so I found and built
> > > > a 455Khz crystal oscillator circuit, with a variable output
> > > > level by way of a pot in the screen voltage.
> > > > The level control is on the front panel.
> > > > The bfo also allows me to copy cw and ssb quite well, without
> > > > a product detector, so I can listen to the ssb guys complain about
> > > > AM.
> > > > The receiver moved into a cabinet on the operating desk, and
> > > > was integrated in the shack with muting and so on, and is
> > > > the main receiver now, the others are almost never used...
> > > > The only problem the receiver has, and it does not bother me, is
> > > > the startup drift. From a cold start, it drifts about 1kc
> > > > over about 5 minutes, then is rock stable.
> > > > This might be due to the choice of octal tubes, the actual tube
> > > > used effects the drift quite a bit.
> > > > Experimentation with npo caps can reduce the drift, but it starts
> > > > drifting the other way over longer periods of time, and I think its
> > > > better to have 5 minutes of drift and stop, rather than drift less
> > > > but over longer periods of time.
> > > >
> > > >
> > > >
> > > > I was quite surprised about how easy it was to build, and how much
> > > > raw fun it was to design the thing, and do all the testing
> > > > and development.
> > > > You sure do learn a lot when you build something step by
> > > step, without
> > > > any overall design to start with.
> > > > Every system must be analyzed, built, tested, changed, other
> > > > things tried, etc.
> > > >
> > > > The end result looks a little rough inside, as it was
> > > > changed quite a bit, deleting the RF amp, adding band switching,
> > > > etc, but it still looks ok.
> > > > Its been totally reliable and stable for about a year now, with
> > > > quite a lot of use.
> > > >
> > > > My next project is a superhet receiver using 7 and 9 pin
> > > tubes, using
> > > > things I learned from the first one:
> > > >
> > > > Start off with band switching,
> > > > Forget the RF amp, its not needed on the low bands at all,
> > > > Do NOT leave a lot of space between things, but put the
> > > tube sockets
> > > > and IF cans close together as possible, along with the local
> > > > oscillator parts and band switch.
> > > >
> > > > It will also include two filters, 4.5Kc, and 5.5Kc.
> > > > The 5.5 was a great overall choice, but a 4.5 will help
> > > > when things get crowded on the bands.
> > > >
> > > > Building a good receiver for AM reception is not as hard as most
> > > > people think, and I encourage people to give it a try.
> > > >
> > > > I have no formal electronics background, all I know I got out
> > > > of books and by playing around, so if I can do it, almost
> > > > anyone can.
> > > >
> > > > Parts are not a limitation, although it may take some time
> > > to assemble
> > > > all you need at a reasonable cost.
> > > > Things like IF cans can be got out of old tube radios, old table
> > > > top AM radios are a good source of parts, as well as mouser
> > > > electronics, Antique electronic supply, ham fests, even
> > > radio shack.
> > > >
> > > >
> > > > You may find you can build something better than anything you can
> > > > buy for almost any price, as YOU pick what is important,
> > > > I only wanted part of 80 and 40 meter coverage, low noise, and hi
> > > > fidelity, along with reasonable frequency resolution.
> > > >
> > > > Old tube receivers like the Scott SLRM, SX17, SX28 can be quiet and
> > > > hi fidelity, but lack frequency resolution, good filters, and cover
> > > > more bands than I need.
> > > > Newer tube receivers like the R390 series, the Collins 75a series,
> > > > the National nc300/303, Drake and others have some good points,
> > > > but lack fidelity, bandwidth choices, look ugly as stink,
> > > or have some
> > > > other drawback.
> > > > All new ham equipment seems to be very high in noise and
> > > distortion,
> > > > and you may THINK some of that stuff sounds good, until you
> > > > compare it to a good AM signal through an old tube hi fidelity
> > > > receiver like the Scott SLRM or the SX17.
> > > > Even with output from the detector into a good hi fidelity
> > > > amp and speaker, there is no comparison between the new and
> > > > old stuff on AM.
> > > > I integrate all the receivers into the Marantz amp, and I can
> > > > jump between various receivers quickly, all tuned to the same
> > > > signal, and the difference is dramatic.
> > > > I have tested many, Kenwood ts440, icom 735, Kennwood r1000,
> > > > IC 756pro, and others, and they are all poor receivers for AM
> > > > if you want fidelity.
> > > >
> > > > Brett
> > > > N2DTS
> > > >
> > > >
> > > >
> > > >
> > > > _______________________________________________
> > > > AMRadio mailing list
> > > > AMRadio at mailman.qth.net
> > > > http://mailman.qth.net/mailman/listinfo/amradio
> > >
> > >
> > > _______________________________________________
> > > AMRadio mailing list
> > > AMRadio at mailman.qth.net
> > > http://mailman.qth.net/mailman/listinfo/amradio
> > _______________________________________________
> > AMRadio mailing list
> > AMRadio at mailman.qth.net
> > http://mailman.qth.net/mailman/listinfo/amradio
>
> --__--__--
>
> Message: 2
> Date: Fri, 17 Oct 2003 09:02:23 -0400
> From: Brett Gazdzinski <brett.gazdzinski at mci.com>
> Subject: RE: [AMRadio] FW: Homebrew receiver
> To: amradio at mailman.qth.net
> Reply-To: amradio at mailman.qth.net
>
> Dave,
> I always loved the Collins receivers, but they were very poor
> for AM work, as I guess you know.
> When AM was in, the technology did not seem to support
> good filters, xtal filters were in, or low frequency IF
> stages, both had drawbacks for hi fidelity AM reception.
> When mechanical filters came out, the move to ssb was already
> in motion, so Collins concentrated on building a good ssb receiver
> for ham use. They were very successful.
>
> I don't think Collins ever designed a good audio output stage
> in anything they built, not like the direct coupled, push pull
> output amp like the Scott receivers had, or the hi power
> push pull output some of the Hallicrafters receivers used.
>
> They were not alone, and the best sounding audio receivers were
> built at a time when some of them were used as hi fidelity
> amplifiers for other things, my Scott has a phono input...
>
> The Collins receivers could be upgraded easy these days, with an add on
> low distortion AM detector, and good filters, into an outboard
> audio amp.
> Anything that uses a 455Khz IF frequency can be upgraded
> quite a bit with the kiwi filters, you can tack on a new detector
> without any trouble, and all the Collins receivers were very accurate
> in frequency, very stable, with good frequency resolution.
>
> One of these days, I will get around to upgrading a 75S1 for
> hi fidelity AM reception. Those receivers are still quite reasonable
> in price, and nice and small.
> I had one some time ago, but sold it.
> On AM, it was as broad as a barn door, but I did not know about
> the kiwi filters then.
>
> Way back, when receivers like the NC303 were at fests for $50.00,
> I don't think you could come up with anything better for AM reception.
> Some older radios had better fidelity, but had poor (or no) frequency
> resolution, poor bandwidth shape factors, and other problems.
> I think only the R390 with outboard audio was in the ball park.
>
> Its quite surprising that the NC300/303 still sells for a reasonable
> price these days....when you see them, they are well under
> the cost of something like a 75a4.
> Once and a while, I see them for $200.00 or less.
> That is a lot of receiver for the price!
>
> Brett
> N2DTS
>
> > -----Original Message-----
> > From: amradio-admin at mailman.qth.net
> > [mailto:amradio-admin at mailman.qth.net]On Behalf Of David Knepper
> > Sent: Friday, October 17, 2003 8:21 AM
> > To: amradio at mailman.qth.net
> > Subject: Re: [AMRadio] FW: Homebrew receiver
> >
> >
> > Very fine, Brett. In all the receivers that I have at the
> > Collins Radio
> > Center, I like the NC-303, the best for AM
> >
> >
> > Dave, W3ST
> > Secretary to the Collins Radio Association
> > Publisher of the Collins Journal
> > www.collinsra.com
>
> --__--__--
>
> Message: 3
> From: "David Knepper" <cra at floodcity.net>
> To: <amradio at mailman.qth.net>
> Subject: Re: [AMRadio] FW: Homebrew receiver
> Date: Fri, 17 Oct 2003 09:29:49 -0400
> Reply-To: amradio at mailman.qth.net
>
> Thanks, Brett for these delightful thoughts on receivers.
>
> Very informative.
>
> Dave, W3ST
> Secretary to the Collins Radio Association
> Publisher of the Collins Journal
> www.collinsra.com
> ----- Original Message -----
> From: "Brett Gazdzinski" <brett.gazdzinski at mci.com>
> To: <amradio at mailman.qth.net>
> Sent: Friday, October 17, 2003 9:02 AM
> Subject: RE: [AMRadio] FW: Homebrew receiver
>
> > Dave,
> > I always loved the Collins receivers, but they were very poor
> > for AM work, as I guess you know.
> > When AM was in, the technology did not seem to support
> > good filters, xtal filters were in, or low frequency IF
> > stages, both had drawbacks for hi fidelity AM reception.
> > When mechanical filters came out, the move to ssb was already
> > in motion, so Collins concentrated on building a good ssb receiver
> > for ham use. They were very successful.
> >
> > I don't think Collins ever designed a good audio output stage
> > in anything they built, not like the direct coupled, push pull
> > output amp like the Scott receivers had, or the hi power
> > push pull output some of the Hallicrafters receivers used.
> >
> > They were not alone, and the best sounding audio receivers were
> > built at a time when some of them were used as hi fidelity
> > amplifiers for other things, my Scott has a phono input...
> >
> > The Collins receivers could be upgraded easy these days, with an add on
> > low distortion AM detector, and good filters, into an outboard
> > audio amp.
> > Anything that uses a 455Khz IF frequency can be upgraded
> > quite a bit with the kiwi filters, you can tack on a new detector
> > without any trouble, and all the Collins receivers were very accurate
> > in frequency, very stable, with good frequency resolution.
> >
> > One of these days, I will get around to upgrading a 75S1 for
> > hi fidelity AM reception. Those receivers are still quite reasonable
> > in price, and nice and small.
> > I had one some time ago, but sold it.
> > On AM, it was as broad as a barn door, but I did not know about
> > the kiwi filters then.
> >
> > Way back, when receivers like the NC303 were at fests for $50.00,
> > I don't think you could come up with anything better for AM reception.
> > Some older radios had better fidelity, but had poor (or no) frequency
> > resolution, poor bandwidth shape factors, and other problems.
> > I think only the R390 with outboard audio was in the ball park.
> >
> > Its quite surprising that the NC300/303 still sells for a reasonable
> > price these days....when you see them, they are well under
> > the cost of something like a 75a4.
> > Once and a while, I see them for $200.00 or less.
> > That is a lot of receiver for the price!
> >
> >
> > Brett
> > N2DTS
> >
> >
> > > -----Original Message-----
> > > From: amradio-admin at mailman.qth.net
> > > [mailto:amradio-admin at mailman.qth.net]On Behalf Of David Knepper
> > > Sent: Friday, October 17, 2003 8:21 AM
> > > To: amradio at mailman.qth.net
> > > Subject: Re: [AMRadio] FW: Homebrew receiver
> > >
> > >
> > > Very fine, Brett. In all the receivers that I have at the
> > > Collins Radio
> > > Center, I like the NC-303, the best for AM
> > >
> > >
> > > Dave, W3ST
> > > Secretary to the Collins Radio Association
> > > Publisher of the Collins Journal
> > > www.collinsra.com
> >
> > _______________________________________________
> > AMRadio mailing list
> > AMRadio at mailman.qth.net
> > http://mailman.qth.net/mailman/listinfo/amradio
>
> --__--__--
>
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> AMRadio at mailman.qth.net
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>
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