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Consider using the SR40 as an 'IF strip', preceeding it with a MMIC
preamp, some bandpass filtering, and a Diode Balanced Mixer
using an AMQRP DDS module as the LO source.

I have done that very thing with excellent results.

I've converted my SR40 to 30 meters, and use 10.138 mHz as the IF
center frequency. I've located the LO above the incoming signal in
order to reduce image frequencies.

The output of the DDS module ranges from 11.9 mHz on 160 meters to
31.6 mHz on 15 meters. By replacing the DDS module with the newer 60
mHz model when it becomes available, coverage will be increased to
include the 12, 10 and 6 meter bands.

With the LO above the incoming signal, the radio operates on the lower
sideband. However this can be corrected by software for bands that
require USB operation.

Band switching is accomplished by programming my DDS VFO controller
() so that each of the
eight programmable configurations represent a band. This gives me a
bandswitching VFO with wrap-around, up/down frequency control or
direct entry, variable VFO steps, sweep and scan functions, and 20
memory cells per band.

Presently I am switching bandpass filters manually, but that will
change with the addition of a band pass filter selection circuit
similar to that found in the 'Software Defined Radio for the Masses'
article. The bandpass filters are also similar to those found in the
QEX article. One of the filters, the one I use most oftenly, covers
the 15, 17, and 20 meter bands.

By using this scheme, the SR40 circuitry is not taxed by trying to
stretch it's operation past the limits of its design since it is
always operating on 30 meters. However the radio itself can operate
from 160M to 6M, with the exception of 30 meters (the IF frequency).
Likewise, since the DDS frequency does not have to be divided by four,
the useable range of the DDS module is extended to include all bands
through 15 meters.

What's next? Add a QSE module, a xmit DBM, some driver amps and WALLA,
an all band transceiver. Then add an HC908 controller to take care of
housekeeping, and a DSP module for operation independent of a
computer; a nice winter project.

I'll upload a block diagram of the radio.

Bob WA6UFQ

Excellent idea, Bob !! That solves a lot of problems caused by "pushing" the existing parts to their limits. Cliff was talking about doing that at one of the breakfasts but I don't think he's built his SR-40 yet.

73 Kees K5BCQ

Hi,

This is the path that I started down over a year ago. I was going to
basically duplicate the front end and 1st mixer of the K2 along with
most of the K2's PLL. The K2 uses a DAC tuned PLL reference to fill
in the 5 Khz steps of the PLL. Using the software NCO I could "fill
in" the PLL steps in software instead of using the DAC tuned reference
osc. The K2 uses an approx. 5 MHz IF so I was going to have a 20 Mhz
xtal osc into a divide by four counter to drive the QSD. This
arrangement would give coverage of 160 - 10m. Unfortuanetly, the more
you get into a design like this you begin to see that a lot of the
performance advantages of the QSD are now compromised.

73 de Phil N8VB

--- In softrock40@..., "Bob Hillard" <rhillard@a...>
wrote:

Consider using the SR40 as an 'IF strip', preceeding it with a MMIC
preamp, some bandpass filtering, and a Diode Balanced Mixer
using an AMQRP DDS module as the LO source.

I have done that very thing with excellent results.

.............

That is very good news. A while back I posted a message (No. 484)
suggesting the same but did not get any feedback. I suppose 6m is not
a high priority to the readers of this group.

It would be very interesting if you could post some results regarding
your experiments.

Why didn't you use 9MHz as IF frequency? You could also have the 30m
band?

Jean-Claude Abauzit, PJ2BVU

If you are going to put a pre-amplifier in front of the QSD that I would suggest a better pre-amplifier than a MMic chip. They don't have the best IP3 figures in the world and can have a lot of noise.

A Norton amplifier will be low noise and can have a very high IP3, for best results a Norton amplifier configured in a push-pull configuration will add even harmonic cancellation to boot.

At 09:12 PM 10/28/2005, Bob Hillard wrote:

Consider using the SR40 as an 'IF strip', preceeding it with a MMIC
preamp, some bandpass filtering, and a Diode Balanced Mixer
using an AMQRP DDS module as the LO source.

I have done that very thing with excellent results.

I've converted my SR40 to 30 meters, and use 10.138 mHz as the IF
center frequency. I've located the LO above the incoming signal in
order to reduce image frequencies.

The output of the DDS module ranges from 11.9 mHz on 160 meters to
31.6 mHz on 15 meters. By replacing the DDS module with the newer 60
mHz model when it becomes available, coverage will be increased to
include the 12, 10 and 6 meter bands.

With the LO above the incoming signal, the radio operates on the lower
sideband. However this can be corrected by software for bands that
require USB operation.

Band switching is accomplished by programming my DDS VFO controller
() so that each of the
eight programmable configurations represent a band. This gives me a
bandswitching VFO with wrap-around, up/down frequency control or
direct entry, variable VFO steps, sweep and scan functions, and 20
memory cells per band.

Presently I am switching bandpass filters manually, but that will
change with the addition of a band pass filter selection circuit
similar to that found in the 'Software Defined Radio for the Masses'
article. The bandpass filters are also similar to those found in the
QEX article. One of the filters, the one I use most oftenly, covers
the 15, 17, and 20 meter bands.

By using this scheme, the SR40 circuitry is not taxed by trying to
stretch it's operation past the limits of its design since it is
always operating on 30 meters. However the radio itself can operate
from 160M to 6M, with the exception of 30 meters (the IF frequency).
Likewise, since the DDS frequency does not have to be divided by four,
the useable range of the DDS module is extended to include all bands
through 15 meters.
?
What's next? Add a QSE module, a xmit DBM, some driver amps and WALLA,
an all band transceiver. Then add an HC908 controller to take care of
housekeeping, and a DSP module for operation independent of a
computer; a nice winter project.

I'll upload a block diagram of the radio.

Bob WA6UFQ





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Cecil Bayona
KD5NWA
I fail to see why doing the same thing over and over and getting the same results every time is insanity: I've almost proved it isn't; only a few more tests now and I'm sure results will differ this time ...

--- In softrock40@..., KD5NWA <KD5NWA@c...> wrote:

If you are going to put a pre-amplifier in front of the QSD that I
would suggest a better pre-amplifier than a MMic chip. > >

Yahoo! Groups Links

I would 'not' use a pre-amplifier stage.

In the QEX article a gain of 6 was obtain from the input transformer
which should be enough to overcome the losses in the BPF. Need to run
the AADE program to verify.

The rule of thumb for the design of an RF stage is give it just enough
gain to overcome the tuned circuit losses. T1-4 does this plus
provides a degree of isolation.

I would use high Q inductors (not the store purchased ones) and high
quality RF capactors in the BPF.

Sometimes less is better. At least in this case this appears to be
true.

Stan AK0B

The first device in the received signal's path determines the system's
noise figure. If it's a DBM, then the noise figure can't be any better
than 6 dB. Putting a low noise preamp in front of the DBM fixes this.

The transformer at the input to the SDR will have no effect on the
system noise figure.

Bob WA6UFQ

--- In softrock40@..., "Bob Hillard" <rhillard@a...>
wrote:

The first device in the received signal's path determines the

system's

noise figure. If it's a DBM, then the noise figure can't be any

better

than 6 dB. Putting a low noise preamp in front of the DBM fixes

this.

I seem to remember reading some place the QSD mixer had a noise
figure
in the area of 12 db ? Would this not be acceptable except maybe
above 28 mhz since the terrestial noise figure would be >15 db?

It would be interesting to see a gain/noise chart by stages of the
better commerical receivers when compared to the SDR-1000
technologies.

Does anyone know the maximum usable gain of a receiver(?) aren't we
getting very close to that number in current HF technology?

Are we not close to the point where the LO phase noise and front end
IMD are the current limiting factors in a receiver design?

I would be interested in reading others response in these area. It
is an area in which I know very little.