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FW:RE: SDR hardware - RE: W3SZ's files (David Garnier Oct 17 2002)

-----Original Message-----
From: owner-linrad@xxxxxxxxxxxxxxxxxxxxx
[mailto:owner-linrad@xxxxxxxxxxxxxxxxxxxxx]On Behalf Of David Garnier
Sent: Thursday, October 17, 2002 2:15 AM
To: linrad@xxxxxxxxxxxxxxxxxxxxx
Subject: Re: [linrad] SDR hardware - RE: W3SZ's files


You can buy direct from MiniCircuits, I have a box of parts next to me I
purchased recently, they will deal to hobbists. ( I bought 3 pieces of a
SBL-1X, TUF-1 and some MAR's. The only surprise I ran into was the
requirement of 10 piece mins for their monolythic amps, so  I bought
10 each.  (We are talking about a buck to a buck an a half each, big deal.)
I did ask about purchasing some smaller quanities of some some ERA's
but wasn't that committed yet.)  I asked about mainline distributors, they
don't.  They have a distribitor who I was told would be willing to sell
smaller quanities of their monolythic amps.  I would give them a call
again.  Good Luck.

dave garnier - wb9own

josh-linrad@xxxxxxxxxxxx wrote:

> I would like to build a receiver so I'm going to ask some more questions
> about how all of these pieces fit together.
> On Wed, 16 Oct 2002, Leif Asbrink wrote:
> > If you want something to start with, I recommend you to get two +7dBm
> > schottky mixers from Minicircuits. Mount them in separate little boxes
> > with two RF coaxial connectors (BNC for example) and one audio connector
> > on each box. You may also buy mixers from Minicircuits that are already
> > supplied with connectors.
> OK, so I want to order some mixers.  Minicircuits does not seem to accept
> orders, but DEM has a fair amount of mixers available.
> http://www.downeastmicrowave.com/Catalog.htm#filt  (scroll up a tiny bit)
> SBL-1X 1GHz max., 7dBm LO mixer                         8.50
> SYM-14H 100-1370MHz mixer, +17dBm LO, Surface Mount     15.00
> TUF-1 500MHz mixer, small package                       5.50
> TUF-1H 500MHz, 17dBm LO mixer, small package            12.00
> TUF-2HSM 1GHz, +17dBM LO Surface Mount Mixer            14.00
> TUF-5SM 1.5 GHz +7dBm LO                                12.00
> LRFMS-4 Surface mount mixer, 1.9 Ghz, +7dBm LO          12.00
> ADE-3G Surface mount mixer, 2.3-2.7GHz, +7dBM LO        6.00
> Would you suggest a TUF-1, TUF-1H or SBL-1X as a starting point?
> Or a different vendor...
> The mixers with connectors seem rather expensive at $43+ each...
> > Feed the antenna to a T-connector, then feed the two mixer RF ports with
> > cables of equal length from this T.
> OK, this makes since.
> > Find some way to acquire a signal generator capable of giving at least
> > +12dBm power at 50 ohms. Feed the signal generator to another T-connector,
> > then route two cables from it to the LO ports of the mixers, this time
> > the cables should differ by 0.25 wavelength. On the 80 meter band you
> > need 13 meters of RG58 which is not a big problem. The impedance that
> > the signal generator will see is 25 ohms so you have to feed a little
> > more power than the nominal 10dBm to the T-connector to make up for
> > the mismatch.
> Still following you.
> > Likewise the antenna will see a 25 ohm load so there is a small loss of
> > sensitivity that there is no reason to worry about.
> >
> [SNIP info about preamplifiers]
> >
> > The two RF connectors go directly to the RF and to the LO ports of
> > the mixer. You may route the audio connector directly to the IF port
> > but you will get a somewhat better linearity if you route the IF port
> > of the mixer through a 10 uH inductor to the audio connector and also
> > connect the IF port to ground through a series RC link. 50 ohms in
> > series with 10nF. The three components make the IF port see 50 ohms
> > at RF frequencies which is good for IP3. The audio frequencies should
> > not be loaded, there should not be any 50 ohm load at the soundcard input.
> So how does this look.
>       --- (RF)MIXER(IF) --- I --- Sound Card (I)
>       |       (LO)        |
>       |         |         R
> RF ---|   LO----|         C - Ground
>       |         |(1/4WL)
>       |       (LO)
>       --- (RF)MIXER(IF) --- I --- Sound Card (Q)
>                           |
>                           R
>                           C - Ground
> >
> > If you just can make a simple RF amplifier for your favourite HF band
> > you will be surprised by the excellent performance (if the signal
> > generator is good).
> >
> > At HF you would want a noise figure of say 20dB.
> OK, when you say RF Amplifier here you are taling about a preamp again?
> Initially how critical is this?
> > When referenced to 50 ohms the soundcard may have a noise figure
> > around 35dB. Without any amplifiers at all your noise figure might
> > be 45 dB or 50 dB. If you add an RF amplifier with 30dB gain you will
> > have a receiver with "normal" sensitivity for HF bands which will
> > be able to handle signals up to about -30dBm. (A good radio will
> > handle at least -10dBm at a frequency separation of 100kHz)
> I think what you described is very similar to your webpage
> http://ham.te.hik.se/homepage/sm5bsz/linuxdsp/hware/sbl1.htm
> but you moved the 1/4 WL of coax to the LO and you changed the circuit
> ON the IF to the sound card a little.
> > The only difficult part is to make a good LO. (Avoid that to start with)
> Have you look at or found any chips that give you both the LO and the 90
> Deg LO so you don't need ot use coax?
> What type of wave should the signal generator have?  Square, sine?  I'm
> not sure what to look for...
> My current plan was to make a DDS VFO like
> http://www.qsl.net/yo5ofh/projects/dds_vfo_by_n2apb/dds_vfo.htm
> or
> http://www.netppl.fi/~jonverro/ad9854.htm
> Which has Quadrature outputs so I should not need a 1/4 WL of coax
> for each frequency.  But there is a problem:  "The analog outputs are
> -80...-10 dBm. An amplifier stage is needed to drive a standard level
> diode mixer as an RX LO."  How do you amplify the signals?
> Thanks again for everyone input on this.  I'm sure I'll eventually be able
> to answer these questions at this rate!  And I'll have my own pile of
> pieces to experment with.
> BTW, my email is josh@xxxxxxxxxxxx if the list program hides addresses.
> 73, KD7HGL
>                                                         Later, JOSH