Fw: [linrad] For general interest

["Pierre Vanhoucke" <pierre.vanhoucke@xxxxxxxxx>]

----- Original Message -----
From: "Pierre Vanhoucke" <pierre.vanhoucke@xxxxxxxxx>
To: <josh-linrad@xxxxxxxxxxxx>
Sent: Tuesday, August 19, 2003 1:07 AM
Subject: Re: [linrad] For general interest


> Hi Josh et all,
>
> I will try to summarize the article in a few lines:
>
> There is an  argument against putting the phase shift in the RF  path
> because this path has to operate over a wide frequency range. In such
> situation it is difficult to build a phase shift network that has an exact
> 90° phase shift over whole range. This is not true for the local
oscillator
> if  it is operating at a fixed frequency.
>
> On the other hand there is one reason that we might choose to use in-phase
> LO and quadrature RF:  The RF port of diode-ring mixers is often better
> behaved than the LO ports: experimenters who builds their first phasing
rig
> are often amazed at how much difference an LO phase shift pair works when
> connected to mixers than when it is observed with 50 ohms loads on an
> oscilloscope. Often additional capacitors need to be tacked on the bottom
of
> the circuit board at one mixer LO port or the other.
>
> Conclusion: if the phasing receiver needs to operate at a single frequency
> or over a  very narrow band , the benefit of connecting the quadrature
> network to the RF ports instead of the LO ports can outweight the bandwith
> penalty.
>
> The  article further describes different types of quadrature broadband
> networks and the usage of digital circuits to provide accurate 90 °phase
> shifts for the LO ports. If this digital  approach for LO works better
than
> the quadrature networks , then the previous conclusion is of coarse
reversed
> . However at this moment there is apparently  not enough well documented
> information available about the succes of  this digital approach, which
> leeds  the author to the conclusion that experiments in that area are
highly
> encouraged.
>
> Hope this was helpfull.
>
> I myself plan to carry out experiments in the future with both different
> types of feeding the LO ports, and will keep you informed about the
results.
>
> Best 73,
>
> Pierre /ON5GN
>
>
> ----- Original Message -----
> From: <josh-linrad@xxxxxxxxxxxx>
> To: "Pierre Vanhoucke" <pierre.vanhoucke@xxxxxxxxx>
> Sent: Monday, August 18, 2003 10:36 PM
> Subject: Re: [linrad] For general interest
>
>
> >
> > Please post the answer to the list.  I know I would like to know the
> > answer, but do not have the book, and I probably will not get the book
in
> > the near future...
> >
> > 73, KD7HGL
> >
> > Later, JOSH
> >
> > On Mon, 18 Aug 2003, Pierre Vanhoucke wrote:
> >
> > > Hello Ron,
> > >
> > > An  answer to your  question can be found in the book 'Experimental
> methods
> > > in RF DESIGN' ( published by the ARRL ) in chapter 9.6 (page 9.24 to
> 9.27).
> > >
> > > 73,
> > > Pierre/ON5GN
> > >
> > > ----- Original Message -----
> > > From: "W6WO" <ron-skelton@xxxxxxxxxxx>
> > > To: <linrad@xxxxxxxxxxxxxxxxxxxxxx>
> > > Sent: Monday, August 18, 2003 9:27 PM
> > > Subject: [linrad] For general interest
> > >
> > >
> > > > Here are a few sites that might be useful
> > > >
> > > > For comparing sound cards
> > > > http://www.pcavtech.com/soundcards/compare/
> > > > http://www.tracertek.com/comparisonchart.htm
> > > >
> > > > The Skyworks SKY73001-11 (http://www.skyworksinc.com/) is an
> > > > interesting device designed specifically for direct conversion I-Q
> > > > receivers. Brief specs are
> > > > RF 2 -3500 MHz
> > > > IF 0 -100 MHz
> > > > IIP3 +26 dBm
> > > > IIP2 +67 dBm
> > > >
> > > > I have been looking at the noise specifications of  various DC
> > > > regulators which could affect base-band noise levels, there is a
wide
> > > > range.  In summary
> > > >
> > > > At the high end the LM 317 and 337 series have RMS noise levels of
> > > > 0.003% of Vout. The spec states this is over 10 Hz to 10 KHz
> > > >
> > > > The best I could find from Motorola was the MC1723C that seems to
> > > > have very low noise (2.5 uV) this is stated over the range 100 Hz to
> > > > 10 kHz
> > > >
> > > > The MC78L/79L 100 m/A series have noise levels  5V/40 uVrms, 12V/75
> > > > uVrms, 15V/90 uVrms stated to be  in the 10-100 kHz range.
> > > >
> > > > It is reasonable to expect these levels could be reduced by Tantalum
> > > > capacitors at the device output but it seems smart to select low
> > > > noise devices to begin with.
> > > >
> > > > For further immunity the spec for the AD797 amplifier recommends 0.1
> > > > uF and 4.7uF capacitors at the + and - supply pins with <5 mm leads
> > > > to ground.
> > > >
> > > > Now a question.
> > > > In most I-Q demod designs I note the phase shift is applied to the
> > > > LO.  In the simple 40 kHz 2x SBL-1 design that Leif published in QEX
> > > > the shift is applied to the RF. What is the reason for this approach
?
> > > >
> > > >
> > > >
> > > > --
> > > > 73
> > > > Ron
> > > > W6WO
> > > >
> > >
> > >
> >
> >
>

LINRADDARNIL