ZachTek WSPR TX Mini Build Instruction Download Page 16

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Document version 1.1 Page | 16

If it the output is much less in voltage then first double check the frequency of the output so it is not higher
than that the LP filter frequency, eg don’t set it to 14MHz if you are testing a 10MHz filter.

If no signal can be seen then double-check your solder joints.

If everything checks out you are done!

It is time to connect your WSPR transmitter to an antenna and start watching for spots.

Oh yes, nearly forgot. You can open that beer now.

Sweet!

Summary of Contents for WSPR TX Mini

Page 1: ...ring the low pass filter Background The low pass filter removes the overtones from the generated RF square wave and makes the transmitter compliant to use on one amateur band The user will pick what band to use and will build the filter for this band The filter is made up of four capacitors and three inductors The inductors are constructed using toroidal cores and copper wire The capacitors are su...

Page 2: ...Iron 4 Solder 5 Tweezer Get a clear table space with a soldering iron at hand If you print this instruction have it next to you or have a computer next to you if you read it as you go along Remove the link wire on the WSPR TX Mini As a preparation step you may have to remove a link wire from the WSPR board Sometimes a wire is soldered in to help testing it before delivery Just heat up the solderin...

Page 3: ...llow The larger bag also contains two smaller bags that holds surface mount capacitors To avoid getting the capacitors mixed up I recommend that they stay in their bags until it is time to solder them to the board Finally there is also a piece of wire that will be used for the toridal cores Checking out the schematics for the filter If we check the schema we see that the inductors are called L1 to...

Page 4: ...acturing There are two capacitance values in the filter C1 and C4 are smaller in value than C2and C3 The exact value depends on the frequency band the filter is made for To find the value check the SMD low pass filter table in the appendix As an example for a 20m filter C1 C4 are 180pico Farad and C2 C3 are 390pcio Farad As a memory guide to aid in placing the correct values think Higher value cap...

Page 5: ...ar mental memory guide for the inductor size The Higher value Inductor goes in the center The value of the inductors can also be found in the SMD low pass filter table in the appendix So if we for example are doing a 20m filter the L1 and L3 are 773nano Henrys and L2 in the center is 904nano Henry Enough with the theory time to warm up the soldering iron and create some solder smoke ...

Page 6: ...apply some small amount of solder tin to one side of the pads Once you have applied some solder to one side off all the pads for C1 C2 C3 and C4 pick the two capacitors with the highest value they will be soldered on the inner most two pads C2 and C3 Remove them from the bag and the paper strip they come in Only get the two capacitors with the highest capacitance out at this time Let the other two...

Page 7: ...s are fixed and soldered to one side let s go ahead and solder the other pad as well You might want to turn the board around to get the best working angle Be quick when heating and applying solder so you avoid melting the opposite side or else the cap might come lose and move about on the board ...

Page 8: ...e able to keep your tongue straight for the next step time to do the coils Winding the Toroids To repeat from earlier when we discussed the inductors there are three toroids two have the same inductance same number of turns and the third one that sits in the middle of the three has a larger inductance and thus has more number of turns I suggest that you start winding the middle toroid that has mos...

Page 9: ... if you are unfamiliar how to wind toroidal inductors see the winding guide in the appendix After you have wound inductor L2 it s wires are probably a bit long like in the picture Cut the wires down to length leaving about 12mm half an inch Now we need to get the enamel off the ends so they can be soldered To do that first burn the ends with a flame ...

Page 10: ...e soldering iron and some solder If you have done a good job getting the enamel off it should take solder easily if not scrape some more with the knife and pre tin again It is important to get the enamel off or else the coil might not make god contact when soldered in to the board and as a result you might not get a signal trough your filter ...

Page 11: ... top of the board and solder it on the underside so you have to be able to turn the board up side down without the toroid falling out You can hold the toroid in place in some way or you can bend the leads on the underside use whatever works for you Solder the two leads ...

Page 12: ...ter OK well done so far looking good Now continue winding the other two L1 and L3 they have the same number of turns again look in the low pass filter table to find out how many turns to wind Use the same procedure that you used for L2 to wind trim leads tin leads and finally solder in to the board ...

Page 13: ...Document version 1 1 Page 13 The result will look like this Last step is to verify that everything works using the built in signal generator and an oscilloscope ...

Page 14: ...fying the output Connect the board to a PC and start the configuration program Set it in Signal generator mode and pick the correct frequency in the screenshot below I am testing a 30m filter so I have set the signal generator to 10MHz ...

Page 15: ... on the oscilloscope as the picture below shows Check the oscilloscope you should see a nice sinus curve with about 3 3V Peak to peak value at the frequency you have set There is some small amount of loss in the filter so the peak voltage will probably be slightly less in the picture below it is 3 24V that is a very good result ...

Page 16: ...gher than that the LP filter frequency eg don t set it to 14MHz if you are testing a 10MHz filter If no signal can be seen then double check your solder joints If everything checks out you are done It is time to connect your WSPR transmitter to an antenna and start watching for spots Oh yes nearly forgot You can open that beer now Sweet ...

Page 17: ...Document version 1 1 Page 17 Appendix SMD low pass filter table ...

Page 18: ...the normal way of winding and the inductance as measured is 0 46uH The lower one has a much higher measured inductance of 0 77uH There is nothing wrong with the lower inductor if you wanted 0 77uH in your circuit However most designers me included has standardized on winding with turns spread out on the core and calculate the number of turns based on this assumption If you happen to not follow thi...

Page 19: ... you get lost in the count then you can recount the number of turns by using the following rule look at the core from above and count the number of wires that cross the top side of the core se picture for an example of a 17 turn toroid END OF DOCUMENT ...

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