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From: "Alan Melia" <alan.melia@btinternet.com>
To: <rsgb_lf_group@blacksheep.org>
References: <000c01cb7da9$23b1a1e0$8d01a8c0@JAYDELL><AANLkTi=yRa690fcCwJ=b1Lvte2d3EbMGpUH3mAMvs6Q4@mail.gmail.com><4CD6FF00.9090406@telia.com> <AANLkTingx1ggmn8o4h-a5sUgrU-VboACuey8Tc3Ly=GT@mail.gmail.com>
Date: Mon, 8 Nov 2010 00:25:10 -0000
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Subject: Re: LF: exciter for 137 and 500 kHz
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Andy, I am trying to remember now and you probably dont have the kind of
library access now.....but there was a couple of articles in Electronics
World covering this topic with simulation and getting very good (it seemed)
results. I will try and find it in the archive (I have paper copies of that
until it started publishing rubbish two or three years back.) Whether it was
"practical" (or "just software" ) I cant remember now. It covered a number
of techniques including Gingell

Alan G3NYK

----- Original Message ----- 
From: "Andy Talbot" <andy.g4jnt@googlemail.com>
To: <rsgb_lf_group@blacksheep.org>
Sent: Sunday, November 07, 2010 8:46 PM
Subject: Re: LF: exciter for 137 and 500 kHz


> That's a neat bit of software!
>
> But I've noticed in all the all-pass design procedures, there are choices
> of optimising, Monte Carloe-ing, adjusting and tuning the RC  part of the
> networks.  But none seem to take into account the effect of mismatch of
the
> nominally matched pair of resistors around each opamp.   Or of residual
> amplitude mismatching.
>
> But it does seem that if you are prepared to spend the time getting all
> the Rs and Cs within a micro percent of the correct values, then apply the
> same effort to amplitude and phase matching the channels, a quite
phenomenal
> performance wrt. sideband suppression is theoretically possible.
>
> But I guess in any practical scenario, most constructors will tweak for an
> acceptable performance and leave it alone.   For upconverting at LF, we're
> only interested in narrow band signals - the entire WSPR segment is only
> 200kHz wide - and a simple 2 stage (one opamp in each of I and Q) is
> adequate.  In that case a pair of preset or variable resistors can be
> tweaked quite quickly.   40 - 50dB supression seems almost guaranteed over
a
> 100Hz using a predictable mixers like fast CMOS switches, with a
comparable
> level of carrier suppression.  I've built two now, one with FST3125 and a
> balanced output transformer,  and one with a dual quad switch, FST3257.
The
> latter gives somewhat better performance, but is slightly more complex.
>
> Andy
> www.g4jnt.com
>
>
> On 7 November 2010 19:33, Johan H. Bodin <jh.bodin@telia.com> wrote:
>
> > Andy,
> >
> > here's another nice program for all-pass I/Q filter design:
> >
> >  http://www.tonnesoftware.com/quad.html
> >
> > 73
> > Johan SM6LKM
> >
> > ----
> >
> > Andy Talbot wrote 2010-11-06 14:59:
> > > Very Interesting.
> > > Where did you find the design data for the allpass network?   I've
only
> > been
> > > able to find the values for up to 3+3 allpass stages.
> > >
> > > Mind you, at that number of chips a DSPic begins to look attractive.
> > >
> > >
> > > Andy
> > > www.g4jnt.com <http://www.g4jnt.com>
> > >
> > >
> > > On 6 November 2010 11:52, <jrusgrove@comcast.net <mailto:
> > jrusgrove@comcast.net>>
> >  > wrote:
> > >
> > >     Nothing earth shattering ... another way to skin the cat. The 137
and
> > 500
> > >     kHz units have been in use for a few years ... just now getting
> > around to
> > >     the write up.
> > >
> > >     http://www.w1vd.com/137-500Phasingexciter.html
> > >
> > >     Jay W1VD  WD2XNS  WE2XGR/2
> > >
> > >
> >
> >
>