EMRFD Message Archive 3438

Message Date From Subject
3438 2009-08-07 21:14:40 rcbuckiii General Coverage Receiver
Harold (W4ZCB)made this comment in the discussion of Measuring Crystal Parameters:

You pay a price for a radio that is "general coverage" upconverting. And he gives the reasons why this is a problem.

I was thinking of taking this approach to build a general coverage receiver and was going to use either 45 MHz or 75 MHz for the first IF. Harold based on your comments, what would be a better scheme? I don't need superior performance. Just pretty good performance since it will be used for casual listening purposes.

Also, what recommendations would others have as the IF scheme that could be employed?

Ray
AB7HE
3439 2009-08-07 21:41:36 Dave - WB6DHW Re: General Coverage Receiver
rcbuckiii wrote:
> Harold (W4ZCB)made this comment in the discussion of Measuring Crystal Parameters:
>
> You pay a price for a radio that is "general coverage" upconverting. And he gives the reasons why this is a problem.
>
> I was thinking of taking this approach to build a general coverage receiver and was going to use either 45 MHz or 75 MHz for the first IF. Harold based on your comments, what would be a better scheme? I don't need superior performance. Just pretty good performance since it will be used for casual listening purposes.
>
> Also, what recommendations would others have as the IF scheme that could be employed?
>
> Ray
> AB7HE
>
>
>
>
>
Zero IF can be a good approach for narrowband (CW,AM, SSB). Look at
the various R2 receivers. Also, all the SDR receivers use 0 freq IF.
An Si570 programmable oscillator and a simple SDR with a set of bandpass
filters makes a good general coverage receiver. The Softrock40 group
talks about the Softrock series designed and sold by Tony, KB9YIG. I
also have my UHFSDR board and my 995x boards that make good general
coverage receivers(the UHFSDR also transmits).

Dave - WB6DHW
<http://wb6dhw.com>
3440 2009-08-08 05:04:42 w4zcb Re: General Coverage Receiver
>I was thinking of taking this approach to build a general >coverage
>receiver and was going to use either 45 MHz >or 75 MHz for the first
>IF. Harold based on your >comments, what would be a better scheme? I
>don't need >superior performance. Just pretty good performance >since
>it will be used for casual listening purposes.

Not sure. I make my radios as good as I can. As far as the phase noise
parameter, since it gets worse with increasing frequency, I suppose
that the 45 MHz IF might be the better choice of the two. If you're a
dedicated general coverage afficionado, I suppose you might go with
Marteins AD9910/9912 DDS and a clean 1 GHz clock and divide the output
down for a very good general coverage receiver, if you're just looking
for pretty good, why not just a SA612 and 45 MHz IF strip? Never had a
lot of interest in frequencies I couldn't TX on.

W4ZCB
3441 2009-08-08 06:54:06 Rick Re: General Coverage Receiver
Another old idea worth considering is a conventional single conversion shortwave radio with 455 kHz IF, but with a new I Q local oscillator and image-reject converter.

The modern term for a receiver with single conversion to a low IF is "Near Zero IF." It's a popular architecture for microwave receivers.

The two significant performance flaws of old shortwave radios are frequency drift and poor image rejection on the higher bands. This scheme attacks both problems.

For ham-band only applications, the front-end filters I'm now using are good enough that a 455 kHz IF is practical up through at least 14 MHz even without an image-reject front end.

In a general coverage receiver, one of the biggest headaches is internally generated spurs. Single conversi
3442 2009-08-08 09:35:54 Fernando Krouwel Re: General Coverage Receiver
Hi Rick, good afternoon:

Very good sugestion about low IF´s.

I have some Collins 64 KHz mech filters (really big ones) taken from old junk boards of Frequency Division Multiplexers, center frequency 64 KHz (some of them are 2.9 KHz wide and others 3.1 KHz wide) that could use this technique.
I will think carefully about using them with phasing techniques to eliminate images with single conversion near zero IF (in this case 64 KHz). Is it possible to use an efficient phase shifting network scheme (at 64 KHz) to eliminate images (specially on 10, 6 and 2 meters)? What could be the best one (I have the book EMRFD)?
Obs.: I want to have a complete receiver, independent from computers, not SDR.

73´s
Fernando - PY2ETT


----- Original Message -----
3443 2009-08-08 10:31:24 rcbuckiii Re: General Coverage Receiver
3444 2009-08-08 11:31:11 w4zcb Re: General Coverage Receiver
>It has been an idea I have been kicking around for a while. It would
>give me a chance to build something fairly >complex that can be used
>for casual listening. I had also thought about using a DDS for the
>first oscillator so I could >pretty much choose any IF that I wanted.
>And single conversion would probably be better than double
>conversion. >I'm somewhat concerned about phase noise from the DDS
>but for a general purpose receiver it may not be much of >an issue.

There's almost no phase noise from a DDS. Aside from spurs, which
really are not a problem if you pay attention to the construction and
shielding, (My 9951 with a 125 MHz clock has a few spurs on 10 meters,
only 2 of which are above MDS at some -126 dBm.) They're a lot quieter
than an LC oscillator and a whole lot quieter than any PLL I've ever
made.

W4ZCB
3445 2009-08-08 11:41:47 Rick Re: General Coverage Receiver
Hi Fernando,

There are some fast op-amps that will work at 64 kHz in image-reject networks. I might try the network in figure 9.52 with the RC time constants scaled by 1/100 for good rejection from 30 kHz to 112 kHz.

I would be more inclined to use a broadband passive LC network at 64 kHz. There are many more of those than are covered in EMRFD. A good one is in figure 9.40, and includes the equations needed to scale it for a center frequency of 64 kHz. You will want to play with it in a simulator (I use LT Spice) to observe performance and maybe tweak component values, then confirm operation at the bench with 50 ohm terminations.

Another good choice is the IF phasing network used in the Drake R8 receiver at 50 kHz. That network is already optimized for the bandwidths needed in a general coverage receiver, and could be easily moved to 64 kHz. Perhaps someone on this site has access to that circuit, or better yet, knows the designer.

6 and 2 meter phase shift networks are easy--I've used twisted wire hybrids and an in-phase splitter followed by a lumped element quarter wave line on both bands. My instrumentation receivers for measurements and propagation experiments are single-conversion VHF receivers with 15 kHz IF.

One final thought is that 15 kHz (standard for DSP receivers) may be used for an all analog Near Zero IF receiver. Inductors, capacitors and op-amp active filters all work well there, and so do all analog product, diode, and various FM detectors. DSP is cheap, but it's not the only option.

But I'd use those 64 kHz Collins Mechanical Filters in a 64 kHz IF homebrew receiver. That sounds like a fun project.

Best Regards,

Rick kk7b

3446 2009-08-08 12:58:03 leon Heller Re: General Coverage Receiver
----- Original Message -----
3447 2009-08-08 15:05:01 Fernando Krouwel Re: General Coverage Receiver
Hi Rick, good afternoon:

Thank you very much for the very useful sugestions.

I´ll try to find the R8 schematic to compare and choose what seems best performer (and not too much difficult for a modest home lab evaluation...).

73´s
Fernando - PY2ETT

----------


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3450 2009-08-09 06:14:30 timshoppa Re: General Coverage Receiver
3451 2009-08-09 06:54:54 w4zcb Re: General Coverage Receiver
I think that some people don't understand the spurs and think that
they are a characteristic of a bad builder or shielding. When really
they are unavoidable for certain frequency control words, some are
worse than others, and usually there's a nearby frequency control word
giving nearly the same frequency that has doesn't have the same
problem spurs.

Tim N3QE

Certainly spurs at Fclock/Fo(x) are tough. With the 9850, I have
identified spurs that were the result of Fclock/Fo times 25! (Those
suckers really tune fast!) There are several methods of spurious
generation as well, anything at the RX/TX frequency, but also at the
IF frequency. In the PicaStar project we had a lot of success
bandpassing the LO output on 20 meters and above so that the IF as
well as higher order spurious were protected. Carrying that through to
the later 9951, resulted in near spurious free operation and certainly
better than the everywhere phase noise of a PLL. (Better too than the
various unfiltered DDS VFO's that made QST's pages entirely too often.
Those hopefully were all used in QRP rigs where the band damage was
minimal.)

Unfortunately, the general spectrum is becoming more and more
corrupted. During even WW II, it was claimed that cities were
identifiable just by their relative RF signature. God knows how bad it
is now what with BPL, leaky microwave ovens, regen garage door
openers, RFID tags and the endless stream of RF consumer products
flooding us these days. I had a sched with an old friend on 40 at
about 600 miles, and a neighbor who used to chime in on occasion. The
neighbor complained of QRM on frequency that I didn't experience, so
finally one day went to his home after the sched. It immediately
sounded like a harmonic of a switching PSU that repeated about every
75 KHz at some "S"-7 on his RX. I sent him around his home to
disconnect TV sets, VCR's and the like to no improvement to the
situation. I then went to his kitchen and noticed his coffee pot there
still plugged in but turned off. Pulled the plug out of the wall and
his "QRM" disappeared. Damned switcher in that thing that apparently
ran nothing but the clock and timer on the coffee pot.

W4ZCB
3452 2009-08-09 07:40:30 Chris Trask Re: General Coverage Receiver
>
> >
> > >I was thinking of taking this approach to build a general
> > >coverage receiver and was going to use either 45 MHz or
> > >75 MHz for the first IF. Harold based on your comments,
> > >what would be a better scheme? I don't need superior
> > >performance. Just pretty good performance since it will
> > >be used for casual listening purposes.
> >
> > Not sure. I make my radios as good as I can. As far as the
> > phase noise parameter, since it gets worse with increasing
> > frequency, I suppose that the 45 MHz IF might be the better
> > choice of the two. If you're a dedicated general coverage
> > afficionado, I suppose you might go with Marteins AD9910/9912
> > DDS and a clean 1 GHz clock and divide the output down for a
> > very good general coverage receiver, if you're just looking
> > for pretty good, why not just a SA612 and 45 MHz IF strip?
> > Never had a lot of interest in frequencies I couldn't TX on.
> >
> > W4ZCB
> >
>
> It has been an idea I have been kicking around for a while. It would give
> me a chance to build something fairly complex that can be used for casual
> listening. I had also thought about using a DDS for the first oscillator
> so I could pretty much choose any IF that I wanted. And single conversion
> would probably be better than double conversion. I'm somewhat concerned
> about phase noise from the DDS but for a general purpose receiver it may
> not be much of an issue.
>

Using DDS for the 1st LO is not going to be an easy task. DDS devices that go up high enough in frequency tend to be very expensive and power hungry. One way out of it is to use a PIC based DDS as the reference for a PLL, which then acts as a frequency multiplier. This, however, can add additional phase noise and spurs to the output.

Another way around the frequency limitation of DDS is to use a converting LO, which uses a fixed oscillator (crystal or coarse PLL), a wide-band VCO, a mixer, a phase detector and filter, and a low frequency DDS. The two oscillators go to the mixer. The mixer sum is the output, and the difference goes to the phase detector along with the DDS. The phase detector output goes to the loop filter which goes to the VCO.

The frequency difference between the fixed oscillator and the VCO is the same as the frequency of the DDS. Basically, the phase noise of such a system is a the sum of the DDS and the fixed oscillator when inside the loop filter cutoff frequency. There are fewer output spurs due to the loop filter.

A system like this works best with a dual conversion receiver, where a coarse PLL is used for the 1st LO (good phase noise and spurs) and the DDS controlled 2nd LO uses a crystal oscillator.

And a little note about DDS: I devised a method many years ago to easily convert the sawtooth wave output to a triangle wave. It requires eight XOR gates. The output spurs are lower, filtering is much easier if you're not using a PROM lookup table, and if you do use one you only need have as much capacity. I impleneted this in a poor-man's descrete logic DDS with BCD programming, and it works just fine.



Chris

,----------------------. High Performance Mixers and
/ What's all this \ Amplifiers for RF Communications
/ extinct stuff, anyhow? /
\ _______,--------------' Chris Trask / N7ZWY
_
3453 2009-08-09 09:40:19 leon Heller Re: General Coverage Receiver
----- Original Message -----
3454 2009-08-09 18:07:26 timshoppa Re: General Coverage Receiver
3455 2009-08-09 20:06:59 rcbuckiii Re: General Coverage Receiver
3456 2009-08-09 23:04:42 Ashhar Farhan Re: General Coverage Receiver
i recently succumbed and bought an FT 817 after looking around for an
RA6793 for a long time. i desperately need a GRC. is the carrier
oscillator noisy? is my Local oscillator fine? is my post mix over
modulating? how's the amp's inter mod? all these measurements require
a good solid general coverage receiver that will extend from 100 KHz
(i might use the two collins filers in my drawer one day) to 30 MHz.
it almost became a necessity in the shack. this effectively rules out
the monoband receivers that we usually turn out regularly in our
shops.

I will probably use the FT 817 to 'boot' up a homebrew GRC and stow it
away. but, back to the idea of the general coverage receiver ...

the first question is how comfortable are you really with the digital
side of things. if you are unfamiliar with assembly langauge, in
circuit programmers, debuggers, etc. then it is best to skip them. on
the other hand, if this hobby is an escape from that digital world (i
design voip stacks and dabble in codecs for a living), then too it
might be a good idea to stay away from that world.

even so, a conventional superhet that does general coverage may not be
as exotic an animal. here is how.

1. IF choice

upconversion is a good choice. but stability might indicate that you
will need a PLL or DDS. A PLL that swings 30 MHz will require a VCO
that will tune such a wide range. that means, it has a very high
'frequency per volts' sensitivity. this can compromise your
oscillator's phase noise characteristics if the loop amplifier is not
proper.

you can try an HF IF (like the BITX or K2). this is a safe,
conventional choice. but, the IF can now appear inside the tunable
range of the receiver. So, you will live with a 'hole' of about 2 MHz
in the coverage around the IF. you can probably suppress it with
balance and phasing. but that would increase the complexity.

finally, you can choose a low IF (as Rick suggests) or around 455 KHz
or so, where you can deploy an excellent mechanical filter. images can
be a problem above 14 MHz. unless you use more poles or using
quadrature method to suppress the IF image (this will involve
generating 90 phase shift of the LO over a wide range, something that
will require at least a 1 on 1 analog PLL).

2. Local oscillators

Free running oscillators will have to operate in the HF range, and
surely in the upper HF range for coverage beyond 20 MHz. As most of
the capacitance is now from the tuning cap, expect the temperature
stability to be better than with fixed capacitors. it might still not
be enough for anything beyond casual SSB and CW. in that case, you
might want to try out the fast HnP stabilizer (Cumbria Desings has
some nice kits) or on a more radical note, explore a cavity or a
helical resonator (look up EMRFD's CD for Carver's description of his
VHF free running oscillator).

3. Preselectors

Assuming we rule out wide band, 'open' front ends, we can settle for a
tunable, at least double tuned (if not triple tuned), wide range
preselector. the obvious problem in designing such a front end is that
the coupling between resonators cannot be the simple fixed capacitance
(as it's reactance will change with frequeny). you can, instead use
taps on the inductors to couple them with each other, or borrow Wes's
idea of a using an active element (like an low gain FET amp) between
singly tuned stages.

In such a scheme, it should be possible to achieve 'almost general
coverage' with fair performance and using our conventional technology.

- farhan
3457 2009-08-10 04:59:18 rcbuckiii Re: General Coverage Receiver
Farhan,

Thanks for the suggestions. I think my final design will come after a lot of experimentation.

For the wide range PLL I would use some sort of relay switching scheme to cover the neeeded 30 MHz. My experiments in the past have shown me that consistent wide range is difficult to achieve.

I am very familiar with assembly language using PIC and AVR parts. But these days I tend to use C and dsPIC parts for all but the simpliest of projects.

All said it will be a work in progress for the next year or so. But experimenting is what this hobby is all about.

Ray


3458 2009-08-10 06:21:12 timshoppa Re: General Coverage Receiver
3459 2009-08-10 06:53:51 Jim Miller Re: General Coverage Receiver
Tim

could you provide a link to the g3roo oscillator? i couldn't find it at his
website.

tnx
jim ab3cv


[Non-text portions of this message have been removed]
3460 2009-08-10 07:17:08 Chris Trask Re: General Coverage Receiver
>
> All this gives me something to think about. I had originally thought about
> just using a PLL for the 1st oscillator with 1 MHz steps. Then use a
standard
> analog VFO in the 5 MHZ region for tuning purposes with a 9 MHz IF. Once I
got
> that working I was going to try replacing the VFO with a DDS. Another
possibility
> for the VFO would be huff-n-puff. That would certainly be more than
adequate for
> casual listening. What had given me the original idea for a 75 MHz was to
sort of
> duplicate what is in my Yaesu FRG-7. It does a decent job using the Wadley
loop method
>

The receiver system I ended up pursuing has a PLL with 100kHz steps as
the first LO and a converting DDS LO that tunes to 100Hz steps for the
second. Making a discrete logic DDS with 100Hz, 1kHz, and 10kHz BCD tuning
was quite a challenge. Tried to get some people interested in doing a PLA
implementation of it but they disappeared very quickly.

Chris

,----------------------. High Performance Mixers and
/ What's all this \ Amplifiers for RF Communications
/ extinct stuff, anyhow? /
\ _______,--------------' Chris Trask / N7ZWY
_
3461 2009-08-10 08:14:56 timshoppa Re: General Coverage Receiver
3462 2009-08-10 08:42:33 Rick Re: General Coverage Receiver
General Coverage vs. Ham Band: Farhan has taken my approach to this problem. In my shack-lab, my general coverage receiver has been at the center of test equipment stack for decades. It sits on top of my signal generator, right next to my oscilloscope. If I were starting over and had limited space, an FT-817 might be my first purchase as a piece of test equipment. Most of my test equipment is old professional gear purchased inexpensively on the surplus market--but I do spend more on my test equipment than on my ham station.

My receiver projects are always experiments to test some new idea (new to me at least), and the experimental results usually come more quickly if I design and build each receiver for a single band. If I like the performance, I design and build a set of converters (transverters if it's a transmitter-receiver) to get on other bands. That helps break up the project into stages, which not only helps move the project along but limits the variables so that each step in the project only involves one or two experiments.

I have sketched out a number of different general coverage receivers over the years but have not built a serious stand-alone one. Like Farhan, I spend a lot of time professionally dealing with cost-driven digital circuitry that will be obsolete in a few years. It is frustrating to pick up a project in my lab after 5 years and discover that a key piece of the signal-processing software will no longer run. So I enjoy using analog electronics and mechanical hardware when I am free to make those decisions. If I did build a serious general coverage receiver, its block diagram would probably look more like an R-390A than a modern up-converting radio, hi.

These decisions are all personal and each one of us will find different parts of the problem interesting. In Experimental Methods in RF Design it is important for each of us to work
3463 2009-08-10 08:55:28 Chris Trask Re: General Coverage Receiver
>
> The G3ROO details are in most of the ARRL handbooks for the past few
years,
> in the "Oscillators and Synthesizers" chapter. Google for G3ROO and
Synthesizer.
>

I managed to find this in the 1999 handbook on pages 14.45 to 14.49.
This is very much like the converting LO that I have devised, the exception
being that the VFO (F1) and crystal oscillators (F2) are each about half of
the desired output frequency (Fout):

Fout = F1 + F2

and the difference between them is the same as the frequency of the DDS
(Fdds):

Fdds = F1 - F2

The frequency limitation of the DDS drives the choice of frequencies for
the two oscillators, so that:

F1 = (Fout + Fdds)/2

F2 = (Fout - Fdds)/2

This lets you use far less expensive DDS implementations such as the
various PIC-based designs that can be found in numerous places. It also
keeps the crystal oscillator frequency down to a range where you can find
lots of readily-available commercial devices. The only thing that's added
beyond the G3ROO circuit is a very simple diplexer after the mixer.

I also use an analogue quadrature phase detector instead of a digital
phase-frequency detector. This reduces the reference spurs in the output to
the point where there simply aren't any to be found.

Chris

,----------------------. High Performance Mixers and
/ What's all this \ Amplifiers for RF Communications
/ extinct stuff, anyhow? /
\ _______,--------------' Chris Trask / N7ZWY
_
3464 2009-08-10 09:33:51 Rick Re: General Coverage Receiver
The analog quadrature phase detector is a good idea that isn't as well known as the common VLSI XOR and phase-frequency digital detectors. As Chris mentioned, it is superior to the comm
3465 2009-08-10 10:37:54 Chris Trask Re: General Coverage Receiver
>
> >
> > >
> > > The G3ROO details are in most of the ARRL handbooks for the past few
> > years,
> > > in the "Oscillators and Synthesizers" chapter. Google for G3ROO and
> > Synthesizer.
> > >
> >
> > I managed to find this in the 1999 handbook on pages 14.45 to 14.49.
> > This is very much like the converting LO that I have devised, the
exception
> > being that the VFO (F1) and crystal oscillators (F2) are each about half
of
> > the desired output frequency (Fout):
> >
> > Fout = F1 + F2
> >
> > and the difference between them is the same as the frequency of the DDS
> > (Fdds):
> >
> > Fdds = F1 - F2
> >
> > The frequency limitation of the DDS drives the choice of frequencies
for
> > the two oscillators, so that:
> >
> > F1 = (Fout + Fdds)/2
> >
> > F2 = (Fout - Fdds)/2
> >
> > This lets you use far less expensive DDS implementations such as the
> > various PIC-based designs that can be found in numerous places. It also
> > keeps the crystal oscillator frequency down to a range where you can
find
> > lots of readily-available commercial devices. The only thing that's
added
> > beyond the G3ROO circuit is a very simple diplexer after the mixer.
> >
> > I also use an analogue quadrature phase detector instead of a
digital
> > phase-frequency detector. This reduces the reference spurs in the
output to
> > the point where there simply aren't any to be found.
> >
>
> The analog quadrature phase detector is a good idea that isn't as well
known
> as the common VLSI XOR and phase-frequency digital detectors. As Chris
> mentioned, it is superior to the common 4046 type 1 and type 2 detectors
for
> some applications.
>

One thing I should have mentioned about the G3ROO scheme and mine is
that by having the crystal oscillator and VFO frequencies about half of the
output frequency, the chance of spurious outputs due to poor LO-IF and RF-IF
lakeage is lessened by virtue of the fact that the two oscillator
frequencies are as far removed from the output frequency as possible, making
the issue of filtering out the mixer leakage much easier.


Chris

,----------------------. High Performance Mixers and
/ What's all this \ Amplifiers for RF Communications
/ extinct stuff, anyhow? /
\ _______,--------------' Chris Trask / N7ZWY
_
3466 2009-08-10 12:19:22 victorkoren Re: General Coverage Receiver
I don't understand why not use a phasing direct conversion receiver, for example take the SoftRock v9.0 Lite+USB Xtall Receiver with Si570 and Electronically Switched BPF Kit sold for $56 by KB9YIG, use the stand alone Si570 controller sold for $25 by K5BCQ and just add the audio frequency part of the receiver which includes the audio phasing network, filter and audio power amplifier. You can use the original SoftRock receiver output to the audio input of the PC when you want to see the spectrum.
I have such a setup and it is extremely useful as a narrow band spectrum analyzer to test inter-modulation of amplifiers and transmitters.
It is even very easy to receive short-wave AM broadcast band stations because the frequency separation between the stations is 5 kHz and tuning the receiver at 10kHz steps I tune the band one direction, then offset the frequency by 5kHz and scan the band at the opposite direction again at 10kHz steps. The accuracy and stability of the Si570 is so good that I'm perfectly at zero beat with the AM stations and the reception is very good. Don't forget that the Si570 has a very good phase noise and no DSP spurious signals. I would recommend to use better input filters, 8 switched Half Octave filters instead the ones supplied with the SoftRock receiver to attenuate the spurious reception at odd harmonics of the LO. The switching of the filters is supported by the Si570 controller.
Victor - 4Z4ME
3467 2009-08-10 16:49:46 ehydra Re: General Coverage Receiver
Because using an Si570 the fun part is over?

I'm using an integrated digital clock generator for my circuit too. A
tiny TSSOP16 does ALL the clock generation I need in the transceiver.
The added benefit for my modulation scheme is that this also makes all
clocks coherent.

- Henry


--
ehydra.dyndns.info


victorkoren schrieb:
> I don't understand why not use a phasing direct conversion receiver, for example take the SoftRock v9.0 Lite+USB Xtall Receiver with Si570 and Electronically Switched BPF Kit sold for $56 by KB9YIG, use the stand alone Si570 controller sold for $25 by K5BCQ and just add the audio frequency part of the receiver which includes the audio phasing network, filter and audio power amplifier. You can use the original SoftRock receiver output to the audio input of the PC when you want to see the spectrum.
> I have such a setup and it is extremely useful as a narrow band spectrum analyzer to test inter-modulation of amplifiers and transmitters.
> It is even very easy to receive short-wave AM broadcast band stations because the frequency separation between the stations is 5 kHz and tuning the receiver at 10kHz steps I tune the band one direction, then offset the frequency by 5kHz and scan the band at the opposite direction again at 10kHz steps. The accuracy and stability of the Si570 is so good that I'm perfectly at zero beat with the AM stations and the reception is very good. Don't forget that the Si570 has a very good phase noise and no DSP spurious signals. I would recommend to use better input filters, 8 switched Half Octave filters instead the ones supplied with the SoftRock receiver to attenuate the spurious reception at odd harmonics of the LO. The switching of the filters is supported by the Si570 controller.
> Victor - 4Z4ME
>
3468 2009-08-11 07:01:50 timshoppa Re: General Coverage Receiver