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New revision of WSPR Desktop transmitter

Updated: Jan 16, 2020

I have just finished a new revision of the WSPR Desktop.

The new revision use a different GPS module as I had beginning to experience problem sourcing the u-blox Neo-6 module I was using up till now.

I also did a redesign of the low pass filters in this revision.

Instead of a 7-pole filter with hand wound coils I have switched to using factory made coils in a 10-pole filter. See difference in schematic below.

Previous Low Pass filters

New 9-pole Low pass filters

This redesign gives a number of improvements.

1. It will make it possible for me to produce more transmitters as the hand wound coils were limiting my production rate.

2. The new filters have improved performance that will make some filters be able to handle more than one amateur band. This in turn increases the number of bands one transmitter can use for band-hopping.

3 The filters are overlapping nicely without much gaps so the signal generator can be improved in respect to overtone suppression in a future firmware revision.

The new filters has slightly more insertion loss but the power output is still 23dB or more.

I will create a new power versus frequency table soon. Basically the output is around 200mW to 250mW up till above 20MHz and then it goes down very slightly at each band until it reaches 50MHz were it goes down abruptly to 100mW.

It is a huge burden off my shoulders that I don't have to wound 15 coils for each transmitter! See pictures for comparison old versus new revisions.

Old Low pass filters

New Low Pass filters

A great thing with this redesign is that I can release new Low Pass filters types that covers more band. The old low pass filters were broken up in to the "Low", "Mid" and "High" types that covered the following bands: Low: 2190m, 630m, 160m and 80m Mid: 40m, 30m, 20m and 17m

High: 15m, 12m, 10m and 6m

They are now joined with a new type I am calling "MidPlus" that covers the following bands:

MidPlus 160m, 80m, 40m, 30m and 20m

I believe this new MidPlus model will be very attractive for many amateurs as it covers the most used bands 160m to 20m in one little transmitter!

I have a few of these in stock now and are building more so hopefully they will be in stock for a while before running out.

Ohh and the good news is that this improved product will cost the same as the old revisions, in fact they are a few dollars cheaper for a few days now during my Anniversary Sale so get yours while the Sale last for a great deal!



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Harry Zachrisson
Harry Zachrisson
Apr 25, 2020

@Dean, I have plans to extend the firmware to support Type 2 messages so 6letter maidenheads can be sent. But it requires a lot of diving in to the original code by Joe Taylor and understanding it so it will be a while before I have enough time to do that. But it is I'm the plans at least. 73 //Harry


Dean Holmberg
Dean Holmberg
Apr 24, 2020

I have midplus, currently getting a 4 digit grid from the automatic gps setting. Will

We be able to

Get a 6 digit grid?


Hello Harry!

Can you tell anything about when this device will be in stock again?

73 de SM0BPN Uffe


THANKS Harry. Happy New Year.


Harry Zachrisson
Harry Zachrisson
Jan 04, 2020

Hi Daryl. Yes I had a great Christmas break, hope you had as well! But now it is back to work again. I am building more now and they should start getting in to the shop next week starting with the low versions and then followed by the MidPlus and HighPlus some days later or a week after that so check back soon. 73 //Harry

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