Date   

Re: #wspr U3S for 2m WSPR: How to remove the frequency-swing at start of transmission #wspr

Alan de G1FXB
 


On 20/11/2018 21:05, mrdynalink wrote:
So ... back from experimenting. What I did:

1.) I connected a very strongl regulated powersupply with thick wires direct to the U3S mainboard. Hmm ... there was no visible change at all. I played with the supply-voltage, reducing the voltage to 4.8V changed the frequency only for 10Hz. But at start of transmission the "chirp" seems to come from "infinity"...

2.) When I put my finger on the crystal I see the frequency jumping for 100Hz or more. It seems to be very temperature-critical. Somewhere I read that it is a good idea to put a heatsink to the crystal to make the temperature-changing lazy. So I soldered a 2 Cent coin direct on the crystal. But again, no influence to the chirp at the beginning of transmission.

3.) Now I tried to measure the 27 MHz Carrier from the crystal. I connected my Perseus antenna-input direct with the 2 Cent coin and I found the crystal oscillating at 27.005 MHz. Then I tuned the Perseus into the wspr window and made a recording with Argo. This was very interesting:


 
During the pause between the transmissions the crystal frequency makes a big jump. But the crystal should oscillate accurate on one fixed frequency! What is the reason for this behaviour ? Currently I have no idea and have to think about it. Possibly somebody else has an idea for the reason ?

However ... I think it`s a good idea to order the oven-controlled version ... not primary for the oven but for the decoupled 27 MHz oscilator.

Correct,

Perhaps if you take the OXCO route as you have documented characteristics for the Si5351 kit at VHF, it would be a useful half way step to repeat the testing with the OCXO
but with the heater unpowered to purely to observe the improvement brought about by alternative Osc circuit.Before employing the heater option.
Alternatively as others have stated the cheap TCXO's generally have a robust output not to be affected by loading changes.
The FOX has being used in the past, if you search the complete forum thread, another device characterised is :-

https://groups.io/g/QRPLabs/topic/28195580#28671
https://ka7oei.blogspot.com/2018/02/better-frequency-stability-for-qrp-labs.html

The page title is for the ProgRock, but in actual fact the improvements are made solely to the Si5351 module and is applicable to all QRP-Labs kits using the Si5351 kit.
It's smaller than the Fox alternative, but may be worth consideration if you can work with the device?


Alan


73, Henning


Re: #synth ref frequency #synth

DC1MAK
 

merci beaucoup Gilles, many thanks Alan,

i knew, ther was something written somewhere....
in the next weeks i'll try different clocks with
my Arduino-based transmitters....
I'll report my experiences....

73 de DC1MAK micha


Re: #synth ref frequency #synth

Alan G4ZFQ
 

This is explain in assembly manual of Si5351A of QRPLabs.
In this module, a
27MHz crystal is used. This frequency is chosen because it is possible to
configure the chip to produce the exact 1.46Hz tone spacing for WSPR, on
any amateur radio band from 2200m (136kHz) to 2m (145MHz).
What we do not know is just how sensitive the WSPR decoder is to frequency accuracy.
I use 26MHz TCXOs and have decoded my 2m transmissions with no problem.
There was some discussion a few months ago about using even a 10MHz reference for the Si5351 but nobody thought to try WSPR using that.
WSPR has to cope with borderline HF propagation, TX and RX drift.
Without knowing the tolerances of the WSPR decoder it is wise to keep as close to the specifications as possible but I suspect the tolerances are wider than many think.

73 Alan G4ZFQ


Re: #synth ref frequency #synth

F1BFU - Fr - 79
 

This is explain in assembly manual of Si5351A of QRPLabs.

"The SiLabs Si5351A chip is a cousin of the famous and popular Si570 chip, but is much less expensive. Unlike the Si570 however, the Si5351A has no quartz crystal inside. An external reference oscillator or crystal must be provided. The reference frequency may be 25MHz or 27MHz. In this module, a 27MHz crystal is used. This frequency is chosen because it is possible to configure the chip to produce the exact 1.46Hz tone spacing for WSPR, on any amateur radio band from 2200m (136kHz) to 2m (145MHz). A 25MHz crystal cannot provide WSPR tone spacing on the 2m band. In summary, the Si5351A chip synthesizes output frequencies in three stages. The block diagram of the chip is shown to the above (from the Si5351A datasheet). First, a crystal reference oscillator is multiplied up to internal frequency in the range 600-900MHz. There are two PLL’s in the chip, each may be selected to choose a different internal frequency. At the second stage one of the PLL frequencies is divided down to each of up to three required output frequencies. Both the upward multiplication to the internal PLL Output frequency, and the division down to the output frequency, use fractional ratios – an integer plus a fractional part consisting of 20- bit numerator and denominator. Optionally a third division stage may be configured to divide each output by a power of 2, for a maximum division ratio of 128. It is used for generating low frequency outputs between 8kHz and 500kHz."

73 QRO
Gilles F1BFU /Fr

Le mer. 21 nov. 2018 à 21:38, DC1MAK <dc1mak@...> a écrit :
Hi Hans, hi all,

somwhere i read about, that the reference clock of the Silab synth in a U3S MUST be at 27 MHz.
Of course this depends on the firmware of the U3S.
But i think, i heard that there is another cause.
Something with the 1.4648 Hz spacing of the wspr tones ?
Does anybody know about it and can explain that
to me ?



--
Gilles - F1BFU/FR


#synth ref frequency #synth

DC1MAK
 

Hi Hans, hi all,

somwhere i read about, that the reference clock of the Silab synth in a U3S MUST be at 27 MHz.
Of course this depends on the firmware of the U3S.
But i think, i heard that there is another cause.
Something with the 1.4648 Hz spacing of the wspr tones ?
Does anybody know about it and can explain that
to me ?


Re: R36 gain control potentiometer

tk5ep
 

Hi,

If i look on the diagram, R36 has one end grounded. So putting the pot on this side SHOULD produce zero output !
The pot is also a logarithmic version and sound level SHOULD follow a smooth curve.

I suspect that you have a defective pot or something is not correct in your wiring. Check, visualy and with an Ohm-meter, if the ground side of the pot is really connected to ground.

73, Patrick.


QCX output dropped from 5 W to 4W

tk5ep
 

Hi all,

This afternoon i wanted to bridge the reverse protection diode on my 40 m QCX, to save some power drop.

After doing this and putting the board back into the enclosure, i measured the power and noticed that it dropped from 5 W before mod. to 4 W !

I've checked for any problem that could happen during my intervention, but couldn't find anything...

Can the higher voltage (14 V) destroy something ?  I suppose that all 3 x BS170 are still alive, 2 can't probably deliver 4 W ?

Before i go more deeply into the beast, does anyone have any guess ?

73, Patrick.


R36 gain control potentiometer

paul.e.bradshaw@...
 

Hi, 
I have looked for other posts with same problem but could not find exact issue. 
Problem: Gain control (volume) goes from medium to loud but does not turn volume completely down. I've check installation and soldering and was able to adjust and align as per instructions. The QCX works flawlessly other than that. Just wanted some advice before I install into case. This is my very first kit build, new to electronics.

Thank you, 
Paul


Re: #wspr U3S for 2m WSPR: How to remove the frequency-swing at start of transmission #wspr

HF
 

Hi Henning,
In that case, what you're seeing is very much like what I saw before I installed the TCXO which changed chirp and drift to discrete frequency jumps.  Eventually, I lifted the TCXO a couple cm off the PCB, which helped reduce my frequency jumps.  That lead me to wonder whether the TCXO was necessary at all.  But I didn't go back to the crystal to find out.  If the chirp is due to the crystal temperature changing, then lifting it a couple cm off the PCB, connecting it with thin strands of wire (enough to conduct the small current but not enough to conduct much heat), and wrapping it and its coin with foam might help.  Using thin wire would reduce the heat coming in from the foil on the PCB and the PCB itself, and wrapping it with foam would reduce the heat coming in from the PA transistor which warms up at key-down.
Before lifting the crystal, you could back off on the PA's bias and see if the chirp magnitude changes.  This might indicate whether heat from the PA transistor is part of the equation,.
Cheers
Halden


Re: Key Out available?

Hans Summers
 

Hi Jeff

This would not be a good point. The signal there is the Keying signal. What you want, I believe, is a Tx/Rx switching signal. You want the return from TX to RX to occur after a certain delay, after the keying envelope decays to zero. 

A better thing would be to take the "TX" signal from IC3 pin 11 (also available a few other places, please see the schematic). This signal goes HIGH during TX - from the start of the RF envelope starting, to the end of the trailing edge. If you need a signal which has the opposite polarity then take the "RX" signal from IC3 pin 12. 

73 Hans G0UPL

On Tue, Nov 20, 2018 at 10:04 PM <jeff@...> wrote:
I would like to connect my QCX to the MFJ-1708B SDR TR switch using a Key Out from the QCX to feed into the CTRL input on the 1708 rather than depend on the RF sense that it’s capable of.  Would Q4 source be a good point to make this connection or is there a better point in the circuit?
Thanks,
Jeff,  NQ0N


Re: OCXO/Si5351A Oscillator waveform

Hans Summers
 

Hi Kevin

I'd suggest it will all work fine, just proceed regardless.... it is quite difficult to get a decent accurate oscilloscope display at 27MHz even with a high bandwidth 'scope and probes.

73 Hans G0UPL

On Wed, Nov 21, 2018 at 6:41 AM Kevin Luxford <kbgluxford@...> wrote:
Finally got the 27 MHz oscillator working.  Before proceeding with the assembly, I am a bit concerned by the non symmetrical waveform as shown in the attached .jpg file.  Could this be a biassing problem?
Thanks for any advice.
73 Kevin VK3DAP / ZL2DAP
--
Kevington


Re: #wspr U3S for 2m WSPR: How to remove the frequency-swing at start of transmission #wspr

mrdynalink <server@...>
 

Hello Andy,
I`m using parkmode 0. I have only one enabled mode screen so the parking frequency should be the 2m frequency itself?
Yes, I tried transmitting every 4 Minutes but this didn`t changed the "chirp"-behaviour. Later I will make Tests with all park modes.
I`m not sure yet, but I have the feeling that the park-carrier is only replacing the WSPR-transmission but it is off during the seconds between two tranmissions. I will check this detailed ...

73, DF5FH
Henning


Re: Power Output Adjustments And Filter Questions For Beacon Kit With 5W Amp

M0RON
 

Hi Curt, 
App note 4 states use a 25 turns inductor not bifilar wound at 200mw. 
Either set the u3s with a power meter or use the current method of biasing, that should put you somewhere close. Do this before connecting the amp
Andy
--
The universe is made up of Protons, Neutrons, Electrons but contains only one M0RON.


Re: #wspr U3S for 2m WSPR: How to remove the frequency-swing at start of transmission #wspr

mrdynalink <server@...>
 

Hello Halden,
sorry, my fault, I scambled the definitions. I used the word "txco" without thinking. I`m talking about the original Si5351 synthesizer  using the kit-supplied 27 MHz crystal. I have no optional "SMD 27MHz TCXO" in use .

Sorry,
73, DF5FH
Henning


Re: #wspr U3S for 2m WSPR: How to remove the frequency-swing at start of transmission #wspr

M0RON
 

Hello Henning,
Looking at your first screenshot and the second it looks as though you are running from one wspr transmission straight into the next. Have you tried leaving a gap between transmissions? Also what park mode and frequency are you using? 
Andy
--
The universe is made up of Protons, Neutrons, Electrons but contains only one M0RON.


Re: Power Output Adjustments And Filter Questions For Beacon Kit With 5W Amp

Curt M.
 

Thanks for your reply Curt. Anyone have any idea about setting the power output of on the U3S either before or after connecting the U3S to the amplifier?
Curt M


Re: #wspr U3S for 2m WSPR: How to remove the frequency-swing at start of transmission #wspr

HF
 

Hi Henning,
In your first post, you wrote that you were using a txco.  I thought you meant TCXO, so my comments were based on that.  But your recent post refers to a 27 MHz crystal oscillating at 27.005 MHz.  Could you clarify whether you're using a crystal or TCXO in your U3S?
Cheers
Halden


OCXO/Si5351A Oscillator waveform

Kevin Luxford
 

Finally got the 27 MHz oscillator working.  Before proceeding with the assembly, I am a bit concerned by the non symmetrical waveform as shown in the attached .jpg file.  Could this be a biassing problem?
Thanks for any advice.
73 Kevin VK3DAP / ZL2DAP
--
Kevington


Re: Power Output Adjustments And Filter Questions For Beacon Kit With 5W Amp

Curt wb8yyy
 

Curt

I like your idea of biasing and testing the low power U3S first.

Page 2 and 3 clarify how to route RF to the PA and back to the main board. Read carefully, including details to install the bs170 circuit for this app. Yes the LPF goes between the PA and the antenna.

Enjoy your radiations.

The other Curt M


Re: #wspr U3S for 2m WSPR: How to remove the frequency-swing at start of transmission #wspr

mrdynalink <server@...>
 

So ... back from experimenting. What I did:

1.) I connected a very strongl regulated powersupply with thick wires direct to the U3S mainboard. Hmm ... there was no visible change at all. I played with the supply-voltage, reducing the voltage to 4.8V changed the frequency only for 10Hz. But at start of transmission the "chirp" seems to come from "infinity"...

2.) When I put my finger on the crystal I see the frequency jumping for 100Hz or more. It seems to be very temperature-critical. Somewhere I read that it is a good idea to put a heatsink to the crystal to make the temperature-changing lazy. So I soldered a 2 Cent coin direct on the crystal. But again, no influence to the chirp at the beginning of transmission.

3.) Now I tried to measure the 27 MHz Carrier from the crystal. I connected my Perseus antenna-input direct with the 2 Cent coin and I found the crystal oscillating at 27.005 MHz. Then I tuned the Perseus into the wspr window and made a recording with Argo. This was very interesting:


 
During the pause between the transmissions the crystal frequency makes a big jump. But the crystal should oscillate accurate on one fixed frequency! What is the reason for this behaviour ? Currently I have no idea and have to think about it. Possibly somebody else has an idea for the reason ?

However ... I think it`s a good idea to order the oven-controlled version ... not primary for the oven but for the decoupled 27 MHz oscilator.

73, Henning