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Re: [rsgb_lf_group] RE: Cheap and nasty sources - was LF: DK7FC WSPR bad

To: [email protected]
Subject: Re: [rsgb_lf_group] RE: Cheap and nasty sources - was LF: DK7FC WSPR bad quality problem
From: Wolfgang Büscher <[email protected]>
Date: Tue, 29 Mar 2016 18:20:05 +0200
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A modern PIC like the dsPIC33EP32GS202 (which I am currently playing with) can possibly be used for that purpose. It has a multiple high-speed PWM outputs which can be programmed for periods and pulse durations with a resolution of 1.04 nanoseconds (!). The datasheets doesn't clearly state how they achieve this exactly (with a 120 MHz clock frequency feeding the PWM) but this cheap microcontroller, designed especially for switching mode power supplies, looks interesting for LW / MF or even the lower HF spectrum. Possibly the PWM timer is incremented 8 times per 120 MHz cycle, to arrive at the specified PWM resolution.

With software-based cycle stealing (reprogramming the PWM to omit one 1.04-ns-step occasionally) there would be some timing jitter and thus phase noise, but compared with older (slower) PWM units, it's almost neglectable.

Details from the datasheet:

http://ww1.microchip.com/downloads/en/DeviceDoc/70000323g.pdf



73,
   Wolf DL4YHF .

Am 29.03.2016 um 14:54 schrieb Graham:
Andy > PIC
 
If the  execute  times  of PIC  routines  are not  subject to   IRQ  ..or if they are , could be  in a predictable pattern , assuming  nothing else was 'going on'  
 
Then , the  PIC alone  would  produce a reasonable drive  [ square  wave or  pulse]   for  a   class e/d  logic divider  chain , there  being  no  need  [lf/mf]   for the  ppl or dds ?
 
how fast , will  a  pic run?
 
73-G,
 

 
Sent: Sunday, March 27, 2016 9:04 PM
Subject: Re: [rsgb_lf_group] RE: Cheap and nasty sources - was LF: DK7FC WSPR bad quality problem

If you are referring to the close spaced lines making up the spectrum of the two strong signals, from teh plot you show they appear to be about 1.5Hz spacing.  This is the WSPR symbol rate  (actually 1.465Hz) so the lines visible are the natural sidebands from the WSPR waveform.

I'd be surprised if an DDS itself were generating 100Hz sidebands on its own.   Especially a more modern one like the AD9859.    Even the venerable AD9850 doesn't generate stuff only 40dB down.    So I'd still look for other means of 100Hz leakage.   Perhaps getting onto  the reference source.     I assume the two stations both reporting 100Hz sidebands are using identical generating hardware ?

I use an AD9852 for WSPR and generationg MFSK modes generally, a device perhaps bit a bit older than the AD9859, but the same family, and it is certainly clean down to at least -60dBc.   When driven from a higher clock frequency, better still.

Andy  G4JNT


On 27 March 2016 at 19:47, 'Clemens Paul' [email protected] [rsgb_lf_group] <[email protected]> wrote:
 

Hello all,

I've been watching the 100Hz sideband WSPR multi-decodes also from the other two strong stations on MW,
DH5RAE and DB0ABR.They are located about 65km from me and generate S9++dB signals here.
The deoded sidebands are also about 40dB down.
DB0ABR has tried a different power supply to no avail and both believe that the DDS synthesizer is the culprit.
It is a AD9859,see
http://www.dj0abr.de/index_english.html
I have added a perseus screenshot with a bin width of 0.24Hz showing strange lines in their signal.
I'm not sure if this is the DDS spectrum what we see here.

73
Clemens
DL4RAJ

>-----Original Message-----
>From: [email protected]
>[mailto:[email protected]] On Behalf Of Andy Talbot
>Sent: Sunday, March 27, 2016 8:06 PM
>To: [email protected]; [email protected]
>Subject: Cheap and nasty sources - was LF: DK7FC WSPR bad
>quality problem
>
>It is unfortunate these cheap and simple low power solutions
>have come-about at all. The originators who worked out how
>to generate a few milliwatts of Rf from very non-purpose
>designed hardware presumably never anticipated that eh great
>masses would end up connecting this unsuitable kit to high
>power amplifiers. I hope they only ever anticipated their
>being used for very low power uses.
>
>As for the R-PI, that really does look like a bad way of
>generating narrow band RF. I don't know the details of its
>internal hardare, but strongly suspect that it uses a
>jittering Fract-N route to generating arbitrary frequencies.
> Again, fine for a few milliwats of test signal, but
>certainly not for amplification to hundreds of milliwatts.
>
>If you want a decent high power source, use a DDS chip or a
>modern Fract-N synthesizer like the LMX2541. That device has
>an internal VCO and an output divider that allows it to
>generate as low as 35MHz - and then any external CMSO divider
>will allow you to go lower. And they are CLEAN - especially
>so when divided down to LF / HF
>
>
>Andy G4JNT
>
>
>
>
>On 27 March 2016 at 18:14, Graham <[email protected]> wrote:
>
>
>
> Andy,
>
> This time its not really Stefan's fault :-,)
>
> This is a problem , using the raspberry PI , the Pi
>processor uses interrupts, which, cause the execution time
>of the timing loops to vary slightly ,
> the 'small' time variations , produce side bands .
>
> This was evident during the development of a R-PI
>routine for sending Opera , as the R-Pi support
>documentation is not particularly comprehensive, its 'not'
>possible to fully address the i/o functions and as such
>there exists a conflict with higher order irq requests .
>Producing seemingly random widening of the spectrum,
>depending on the irq deployments.
>
> Ie the pulse train suffers from timing jitter
>
> The alterative of the U3 beacon key'er , driving
>the DDS 'oscillator' is a more elegant solution, but as
>noted by Andy [rad-com] some time back, the later U3 with
>the PPL suffers from settling time issues , when
>commanded with , step frequency changes. these sever to
>produce sidebands , at the step changes.
>
> 73-G,
>
>
> From: F6CNI - Andy - JN19QB <mailto:[email protected]>
> Sent: Saturday, March 26, 2016 8:36 PM
> To: RSGB LF Group <mailto:[email protected]acksheep.org>
> Subject: LF: DK7FC WSPR bad quality problem
>
>
> Hello Stefan.
>
>
>
> I am sorry, but this evening you have a very poor
>quality WSPR signal on MF with many splatters, I think it is
>perhaps due to an overload TX AF level.
>
>
>
> That is not in phase with the normal ham spirit. So,
>please be kind to stop now your transmission and correct this problem.
>
>
>
> On the way, can you say honnestly if your power is not
>over the legal limit ?
>
>
>
> Sincerly yours and my best 73 de Andy.
>
>
>
> P.S.
>
>
>
> Have a look below at some reports last hour showing the
>problem :
>
>
>
>
>
>2016-03-26 19:00
>
>DK7FC
>
>0.475683
>
>+12
>
>0
>
>JN49ik
>
>1
>
>PI4THT
>
>JO32kf
>
>336
>
>338
>
>2016-03-26 19:00
>
>DK7FC
>
>0.475783
>
>-25
>
>0
>
>JN49ik
>
>1
>
>PI4THT
>
>JO32kf
>
>336
>
>338
>
>2016-03-26 18:50
>
>DK7FC
>
>0.475783
>
>-23
>
>0
>
>JN49ik
>
>1
>
>PE1RKT
>
>JO22fb
>
>418
>
>316
>
>2016-03-26 18:50
>
>DK7FC
>
>0.475683
>
>+14
>
>1
>
>JN49ik
>
>1
>
>PE1RKT
>
>JO22fb
>
>418
>
>316
>
>2016-03-26 18:40
>
>DK7FC
>
>0.475683
>
>+12
>
>0
>
>JN49ik
>
>1
>
>LA8AV
>
>JO59cs
>
>1153
>
>4
>
>2016-03-26 18:40
>
>DK7FC
>
>0.475783
>
>-24
>
>0
>
>JN49ik
>
>1
>
>LA8AV
>
>JO59cs
>
>1153
>
>4
>
>2016-03-26 18:50
>
>DK7FC
>
>0.475783
>
>-28
>
>0
>
>JN49ik
>
>1
>
>LA3JJ
>
>JO59bh
>
>1102
>
>4
>
>2016-03-26 18:50
>
>DK7FC
>
>0.475683
>
>+10
>
>0
>
>JN49ik
>
>1
>
>LA3JJ
>
>JO59bh
>
>1102
>
>4
>
>2016-03-26 18:40
>
>DK7FC
>
>0.475780
>
>-28
>
>1
>
>JN49ik
>
>1
>
>G3KEV
>
>IO94sh
>
>829
>
>314
>
>2016-03-26 18:40
>
>DK7FC
>
>0.475679
>
>+10
>
>0
>
>JN49ik
>
>1
>
>G3KEV
>
>IO94sh
>
>829
>
>314
>
>2016-03-26 19:10
>
>DK7FC
>
>0.475682
>
>+13
>
>0
>
>JN49ik
>
>1
>
>F6CNI
>
>JN19qb
>
>389
>
>266
>
>2016-03-26 19:10
>
>DK7FC
>
>0.475782
>
>-27
>
>1
>
>JN49ik
>
>1
>
>F6CNI
>
>JN19qb
>
>389
>
>266
>
>2016-03-26 18:30
>
>DK7FC
>
>0.475682
>
>+15
>
>0
>
>JN49ik
>
>1
>
>F5WK
>
>JN18hp
>
>452
>
>261
>
>2016-03-26 18:30
>
>DK7FC
>
>0.475782
>
>-22
>
>0
>
>JN49ik
>
>1
>
>F5WK
>
>JN18hp
>
>452
>
>261
>
>2016-03-26 18:00
>
>DK7FC
>
>0.475680
>
>+19
>
>0
>
>JN49ik
>
>1
>
>DL6II
>
>JO30nx
>
>205
>
>327
>
>2016-03-26 18:00
>
>DK7FC
>
>0.475780
>
>-18
>
>0
>
>JN49ik
>
>1
>
>DL6II
>
>JO30nx
>
>205
>
>327
>
>2016-03-26 18:50
>
>DK7FC
>
>0.475682
>
>+17
>
>0
>
>JN49ik
>
>1
>
>DL4RAJ/2
>
>JN68kj
>
>326
>
>109
>
>2016-03-26 18:50
>
>DK7FC
>
>0.475782
>
>-22
>
>0
>
>JN49ik
>
>1
>
>DL4RAJ/2
>
>JN68kj
>
>326
>
>109
>
>
>
>
>

__._,_.___

Posted by: "Clemens Paul" <[email protected]>
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