Better with SMA

I had some trouble closing the lid on the "Just good enough 10 MHz GPS reference" due to the size of the BNC jack. Therefore I changed it to an SMA (SubMiniature version A) female jack. A thin cable connects it to the K3's SMA input and there is no need for any SMA-BNC adapter on that end.

At the same time I moved the GPS antenna to a more central location in the tin, in the hope that the walls of the tin would interfere less with GPS reception. That's the theory anyway, if it matters much in practice is a different story.

Actually, I think I'm going to use SMA more often with these clear top tins and also Altoids tins. They take up much less space and are easier to install and to work with.

There aren't any high power applications for circuitry in such tins, so I cannot so any reason why the SMA won't work just as well or even better than the BNC.





Other related posts about the 10 MHz reference:

• Just good enough 10 MHz reference (3 Oct 2015)
• Curing amnesia in the 10 MHz GPS reference (19 Nov 2015)
• Improved GPS reception with a ground plane (11 April 2016)

Just good enough 10 MHz GPS reference

Some time ago I noticed that the Ublox Neo-7M GPS has a 10 MHz output which is locked to the GPS system's accuracy. Most people kept saying how useless it was due to excessive jitter unless it was cleaned up with a phase locked loop of some sort.

At about the same time I installed the external reference input for my Elecraft K3. The K3EXREF enables the K3's frequency to be locked to an external 10 MHz reference. What struck me was how its function is described:

• The frequency of the internal oscillator of about 49.38 MHz is continuously measured and averaged, obtaining a value to the nearest 1 Hz.
• The K3EXREF does not phase lock the K3’s reference oscillator and the external 10 MHz source has no impact on the K3’s phase noise performance.

This got me wondering if the Neo-7M would be just good enough as a reference and that all the averaging internally to the K3 would take care of the jitter.

The LM386 Pixie challenge

The Pixie 2 is this minimal transceiver which I and many others have played around with and had lots of fun with. My 80 m version is shown below, but right now it is very popular with some incredibly cheap Chinese ones on sale on Ebay and other places.

The Pixie 2 uses the versatile LM386 amplifier for its audio output. I have shown previously on this blog how its gain can be boosted and how it can implement a CW filter, and also how the muting can be improved. However, during transmission, the LM386 just sits there idle, although it can be used to amplify a sidetone from an external oscillator.

But I'm sure the old 70's LM386 can do better than that. Despite its age, recently some pretty amazing uses of this chip have been demonstrated. It can be used as a regenerative receiver at least up to medium wave frequencies and it can also be used as an envelope detector/demodulator.

The LM386 challenge is this: Is is possible to implement a sidetone oscillator for the Pixie using only the LM386 with as few other components as possible? The output level needs to be controllable in order to make it comparable to that of the Pixie in the receiver mode.

The best data sheet for the LM386 seems to be the one for NJM386 from New Japan Radio Co. It is, as far as I know, the only one which shows the various muting circuits including the one using pin 7 which I have explored. It also shows the LM386 as an oscillator: both a sinusoidal and a square wave one.

In order for the LM386 to be useful as a sidetone oscillator, I believe that the oscillation must take place in the input circuitry. That seems to be the only way to ensure that the output doesn't come out at a blasting full rail-to-rail swing as in the square wave oscillator example in the data sheet.

By the way, the data sheet referred to above is also the basis for the improved Spice model for the LM386 that just was developed. It came partly as a response to my complaint over how poor the present one was. Maybe the new Spice model, developed by EasyEDA, could help solve the LM386 challenge?

Regenerative receiver based entirely on the LM386

I got a tip the other day that there is an interesting circuit over at the RadioBoards Forum where an LM386 IC is used as a regen receiver for the medium wave band. It is the user 'Selenium' who has come up with that circuit. I think it is quite an amazing application of this IC - so here it is:

LM386 as a medium wave regen receiver by user Selenium on RadioBoards Forum

Interestingly, both the + and - inputs are tied together (pins 2 and 3). It is also quite unusual to connect pin 7 to anything but capacitors (for bypass or extra input as I have done), so that may change the bias of the input stage. Further, the smaller the impedance from pin 1 to ground, the larger the gain (here 10 uF in series with 1k for low frequencies and 100 pF for high frequencies).

If you want to read more about the regen circuit, go to the RadioBoards Forum here.

CQ WPX made my day

From time to time I have heard of those of who manage to contact 100 DXCC countries during one weekend. This past weekend it was my turn to try.

If you have a contest station with 1 kW and monoband yagi antennas, then this goal shouldn't be too hard. But for my station with only an 80 m long horizontal loop (loop skywire) circling its way through my garden from treetop to treetop and 100 W of transmitter power from my K3, the challenge was greater.

About 6 hours before the end of the test and with 87 countries, I had almost given up so I sent the tweet above. The status for the second day of the contest was that I had only worked two more countries.

But then in the final hours I heard and then contacted Tunisia, Malaysia, Australia and Kosovo (Z6) to bring me to 91, and then Laos and Albania. But then it took a long while for some new ones: Spanish Africa (EA9) and Argentine. I also managed two more Caribbean stations (J3 and CO) and Peru and Sardinia.

Finally in the last hour of the contest two more Caribbean stations (PJ2 and VP9) and in the end Mexico 21 minutes before the end of the contest. That brought the total to 102. I think that was needed as Kosovo isn't really an approved country and I also had contact with what was probably a pirate and not a station from Andorra. That signature was C31XR which most likely is the name of an antenna and not a real station.

My total was 47 European countries, 19 from Asia, 12 from North America, 10 from Africa, 9 from South America and 3 from Oceania. I think it helps to be in Europe as I had almost half of the countries quite close by, but it would be interesting to hear comments from North Americans on how realistic they consider this goal to be from their location.

Where can I get APF and DIV stickers for my K3?

The updated Elecraft K3, the K3S, has some nice improvements that would be nice to have, but which I also can live fine without. But even an old K3 can be updated to some of these improvements. They are detailed on the Elecraft K3S FAQ.

I studied the front panel for differences and put red rings around them. The three to the upper left have to do with the new display bezel with silver instead of black screws, the S in K3S, a built-in marker for the VFO A knob, and a soft-touch VFO A knob.

In addition to the marking with OFS (offset) to the left of the RIT/XIT control, there are two markings that also reflect what my present K3 with the latest firmware does:

• APF instead of DUAL PB (Audio Peaking Filter - Dual Passband) - upper right
• New marker for DIV - Diversity reception - to the left of VFO A

It sure would be nice to get stickers with APF and DIV to put on mine!

The ultimate WSPR spot

A spot reported by K1JT must be the ultimate goal for the WSPR mode. K1JT, Joseph Taylor, is the Nobel laureate who first developed this mode and other related two-way modes like JT65 and JT9.

My 0.1 W 21 MHz WSPR transmitter regularly makes it over the Atlantic, but never before to K1JT. The SWR was something like 7:1, but apparently that works fine, both for the transmitter and for radiation.

The antenna is a 13 m doublet oriented with the broadside facing East-West (the EU spots in the figure are from my Ultimate 3 on 21 MHz with another antenna and at another location). I feed the doublet with 450 ohm ladder line to a 4:1 Elecraft balun which is connected to the Ultimate 2 transmitter.

Ultimate software is up to date

As I have mentioned several times on this blog, I have thoroughly enjoyed WSPR modes ever since Hans, G0UPL came out with the first Ultimate QRSS/WSPR kit.

That means that I have three different versions of the kit. Since Hans has kept on updating the software and even published the compiled versions, it is also possible to upgrade even the old ones.

I have done that and the displays here show the Ultimate 3, the Ultimate 2, and the Ultimate 1 with the latest software.

It is possible to upgrade the chips in-circuit, but I found that it is simpler to remove the chip temporarily from the socket and move it to a simple veroboard with crystal oscillator components. It is connected to my Ebay version of the USBtinyISP.