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QRP-LABS WSPR U3S issues

 

Picture shows the U3S -deluxe  with PA build into the U3S housing (deluxe). Powered by 12V  1.5A max 1 UA7805 for the U3S 5V, A IRF9510 P-channel + NPN BC557  to make TX 12V switched by the  U3S "key" and an connected  UA7805 for TX5V.  The 5 band LPF board the U3S with the 80m LPF0 not visable the small coax cables to the underside of the U3S to place the LPF 0 and 1 2 3 4 5 behind the PA .  

This multi mode multi band automatic beacon transmitter is a best seller by QRP LAbs kit by Hans Summers
I  build 3 of them, one time they should run as WSPR beacon PU7ZWT in HI11ln  N-E Brasil

Some issues :
Had to replace the original cheap PC 27MHz kristal with a far more stable TCXO Taitien the blue potmeter PCB
More output:

I use an eBay 2 trap HF VHF PA having a RD15HVF1 power Mostfet in the final
RD15xxx Mitsubishi  power MOS-FET are  used in many rigs like the K3 LPA it can operate from HF to 450 MHz. Its Source is  the middle cool flange that makes cooling a lot easier.
This eBay amplifier was original in a smal aluminium case with heat sink. Very sloppy build and poor soldered, but the PCB and design is good 
Also here the PCB is lacking a simple power reflected / forward bridge that could easily have been integrated at design time.  So far only the eBay Chinese 100Watt VHF UHF PCB does offer this simple but very useful item for protection and monitoring.     

I  disabled the first stage un-identified transistor supplied bij 8V from onboard UA7808

The whole first stage circuit did got rather hot and the UA7808 SO89 burnt  had to be replaced by a to220 type from the storage the 8V is also used for the bias voltage for the final RD15 so it can't do without. 

 The U3S  1x BS170 out from C5  is coupled with 3 or 4 windings at the RD15HVF1 input 1:4 bifilar 

It does deliver  3W or more  f.i. 8W at 7MHz  at 11.4V ( 12V -0.6 protection diode)

I took the PA PCB out it fits nicely in the U3S the power RD15HVF is screwed directly at the U3S case and the heatsink is placed under  no or  a small heat sink can do the job the efficiency of the RD15HVF1 MOS-FET is high .  

For use in hot environments a heatsink is not bad.

The U3S is sensitive for RF fields,  with PA intern she became unstable, display garbled. This RFI problem became worse when i modified the RF path so that the U3S the LPF board filters are placed behind the PA as it should be.

I had to do this, the unfiltered output of the PA showed a lot harmonics, at 1.8MHz it was more a square wave form. The power meter reading did not show the real power anymore.

A standard rms power meter then shows unrealistic output levels and efficiency above 80%

The RF did reset the U3S repeatedly since the PA output is lead back over the U3S board first low pass filter and from there switched trough to the extension LPF board with 5 extra LPF.

This makes the RFI problem worse the high level is present on the U3S board now with 2 thin coax   leading to and from the U3S PCB backside. The BS170 trafo T1  output coupling C5 is disconnected from the PCB and connected  to the input of the PA ,  it is originally connected the the input of LPF 0

The output of the PA is connected over thin coax to the point where C5 original was connected. 

To make U3S  RFI stable i placed  100n blocking C's  over the 5V supply and over the 5 relay output lines this had  minimal or non effect but it can't harm.

Most effective is 2 100nF C at the inputs of the Menu and Edit lines back of the U3S board.

No longer RFI resets and display garbling.

Small SMD 0805 100nF fits between the 3 connection entry pins for S1 and S2 push buttons.

Diagrams are on QRP-LABS

TX supply switching is done to keep the power consumption low, the RD15HVF1 needs high bias 0.5 0.9A  

The "key" output  TX=5V  is used to switch an IRF9510  12V TX power for the PA and with U7805 TX5V to the BS170  called PA B+  the BS170 can be supplied external higher than the normal 5V . But better stay with  5V  the BS170 will live longer.

Important:  the PA +B  5V and TX 12V must be switched on together.

 I found TX output did not come in when B+ is not switched strange but observed.

No bias power is lost during idle of the PA and  BS170 .

Summarized short

To make the U3S RFI stable: 2 100nF  at the U3S PCB at the push button input pins.

To minimal frequency drift replace the 27MHz  cheap PC xtal with an TCXO the Taitien TCXO keeps it almost at 1 Hz stable . With the original quartz WSPR drifted too much to decode at 28MHz and higher

A TX switch P-channel FET + TUN  for the TX 12V and PA TX +B  ua7805 5V must be used   

 


50 spots: last night result hopping 80/160/10m

TimestampCallMHzSNRDriftGridPwrReporterRGridkmazMode# Spots
 2021-01-15 01:42  PA0O  3.570196  -25  0  JO33hg  5  DP0GVN  IB59ui  13830  186  2  1 
 2021-01-15 07:36  PA0O  3.570197  -28  0  JO33hg  5  KFS  CM87tj  8804  321  2  1 
 2021-01-15 07:36  PA0O  3.570193  -23  0  JO33hg  5  ND7M  DM16xf  8638  316  2  1 
 2021-01-15 06:52  XE3ARV  3.570143  -20  0  EK59xn  0.2  PA0O  JO33hg  8578  38  2  3 
 2021-01-15 07:36  PA0O  3.570197  -23  0  JO33hg  5  WA5DJJ  DM62ph  8541  307  2  1 
 2021-01-15 07:36  PA0O  3.570197  -27  0  JO33hg  5  KK6PR  CN94ik  8075  324  2  1 
 2021-01-15 04:18  PA0O  3.570196  -28  0  JO33hg  5  K5XL  EM12kp  7982  301  2  2 
 2021-01-15 07:36  PA0O  3.570197  -25  0  JO33hg  5  KA7OEI-1  DN31uo  7960  316  2  1 
 2021-01-15 04:02  K5OK  3.570116  -19  0  EM12qx  5  PA0O  JO33hg  7924  38  2  5 
 2021-01-15 06:36  PA0O  3.570178  -28  0  JO33hg  5  K5OK  EM12qx  7924  300  2  2 
 2021-01-15 04:18  PA0O  3.570197  -23  0  JO33hg  5  KD6RF  EM22  7876  299  2  5 
 2021-01-14 23:04  KD6RF  3.570123  -14  0  EM22lr  5  PA0O  JO33hg  7854  38  2  16 
 2021-01-15 07:36  PA0O  3.570196  -26  0  JO33hg  5  N6GN/K  DN70ll  7714  311  2  1 
 2021-01-15 07:36  PA0O  3.570196  -20  0  JO33hg  5  W3LLA  DN70ln  7706  311  2  1 
 2021-01-15 00:30  W4WLO  3.570041  -19  0  EM50vj  2  PA0O  JO33hg  7647  40  2  26 
 2021-01-15 01:42  PA0O  3.570198  -20  0  JO33hg  5  K9RQ  EL88  7488  288  2  1 
 2021-01-15 02:32  K9RQ  3.570096  -18  0  EL88qm  2  PA0O  JO33hg  7458  40  2  1 
 2021-01-15 01:42  PA0O  3.570196  -20  0  JO33hg  5  N4BUT  EL98ho  7372  287  2  6 
 2021-01-15 01:42  PA0O  3.570193  -18  0  JO33hg  5  W3PM  EM64or  7195  295  2  7 
 2021-01-15 01:42  PA0O  3.570182  -23  0  JO33hg  5  AC0G  EM38ww  7155  301  2  3 
 2021-01-15 02:18  PA0O  1.838195  -26  0  JO33hg  5  WV5L  EM74sc  7105  293  2  3 
 2021-01-15 04:18  PA0O  3.570204  -18  2  JO33hg  5  KK4DF  EM85pf  6905  292  2  1 
 2021-01-15 06:02  KK4DF  3.570086  -16  1  EM85pf  0.1  PA0O  JO33hg  6905  43  2  5 
 2021-01-15 06:54  PA0O  1.838197  -23  0  JO33hg  5  WA0JYF  EN42eb  6867  303  2  1 
 2021-01-15 06:22  AA0N  3.570023  -20  0  EN42fb  5  PA0O  JO33hg  6862  42  2  1 
 2021-01-15 00:18  PA0O  1.838195  -19  0  JO33hg  5  K9AN  EN50wc  6829  300  2  10 
 2021-01-15 01:42  PA0O  3.570197  -23  0  JO33hg  5  AB4DF  EM86ti  6792  293  2  1 
 2021-01-15 05:52  KF9KV  1.837998  -20  0  EN52et  5  PA0O  JO33hg  6694  43  2  5 
 2021-01-15 02:18  PA0O  1.838196  -23  0  JO33hg  5  KF9KV  EN52et  6694  303  2  2 
 2021-01-15 05:58  K9PAW  1.838189  -23  0  EN61ar  1  PA0O  JO33hg  6688  43  2  2 
 2021-01-15 05:42  PA0O  3.570198  -19  0  JO33hg  5  N4LSJ  EM79sf  6686  297  2  2 
 2021-01-15 01:42  PA0O  3.570199  -13  0  JO33hg  5  WD4ELG  FM06be  6652  291  2  7 
 2021-01-15 01:42  PA0O  3.570201  -15  0  JO33hg  5  KA8HUZ  EM79wk  6649  297  2  6 
 2021-01-15 04:18  PA0O  3.570198  -20  0  JO33hg  5  KB9AMG  EN52tx  6611  302  2  5 
 2021-01-15 01:42  PA0O  3.570196  -12  0  JO33hg  5  WB8SCG  FM16qv  6393  290  2  2 
 2021-01-15 01:42  PA0O  3.570198  -15  0  JO33hg  5  K4RCG  FM08si  6392  292  2  11 
 2021-01-15 06:36  PA0O  3.570196  -29  0  JO33hg  5  K8NVH/X  EN82lm  6341  299  2  2 
 2021-01-15 00:18  PA0O  1.838218  -22  0  JO33hg  5  K1HTV-4  FM18ap  6338  292  2  15 
 2021-01-15 01:42  PA0O  3.570165  -13  0  JO33hg  5  K1RA-BB  FM18cr  6322  292  2  5 
 2021-01-15 01:42  PA0O  3.570196  -13  0  JO33hg  5  K1RA-PI  FM18cr  6322  292  2  6 
 2021-01-15 02:48  W8EDU  3.570132  -24  0  EN91  0.2  PA0O  JO33hg  6304  46  2  6 
 2021-01-15 05:42  PA0O  3.570199  -22  0  JO33hg  5  N4AFK  FM18hp  6302  292  2  2 
 2021-01-15 01:42  PA0O  3.570200  -20  0  JO33hg  5  KD4DN  FM18mt  6264  292  2  1 
 2021-01-15 01:42  PA0O  3.570195  -15  0  JO33hg  5  K3KQV  FN00  6262  294  2  6 
 2021-01-15 06:18  PA0O  3.570193  -17  0  JO33hg  5  W0QV  FM18kx  6261  292  2  3 
 2021-01-15 01:42  PA0O  3.570197  -23  0  JO33hg  5  WB2TNC  FM18nx  6245  292  2  6 
 2021-01-15 01:42  PA0O  3.570197  -22  0  JO33hg  5  W3BX  FM19qc  6220  292  2  2 
 2021-01-15 02:18  PA0O  1.838196  -23  0  JO33hg  5  N3RYB  FM19  6217  292  2  2 
 2021-01-15 01:42  PA0O  3.570200  -25  0  JO33hg  5  W3ENR  FM28jh  6194  290  2  4 
 2021-01-15 01:20  PA0O  1.838199  -21  0  JO33hg  5  W2GNN  FN20qh  6004  291  2  8 

Query time: 0.549 sec






 


 


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