24 January, 2016

Latest firmware for AP510 APRS tracker is superb

I got my AP510 APRS tracker a little more than a year ago. It kind of worked, but not very well in my car. But after the tracker got a new firmware dated 3 Nov 2015, it has become so much better. Now I can say that it is really useful.

AP510 with original short antenna
and telescopic antenna
Apparently, the Smartbeacon function didn't work properly in earlier versions of the firmware. With some good debugging and error reporting by KC5EVE, Mark, working with the software developer for the AP510, BG6QBV, the annoying errors now seem to be gone. This is all documented in the Yahoo AP510 group.

I have fitted mine with a 16-45 cm telescopic antenna and even when attached to one of the rear headrests in my sedan, the 1 Watt of output power tracks very well.

The map below shows a drive from Telemark, about 100 km west of Oslo, to Oslo with as good coverage as one can expect given the valleys and the availability of APRS digipeaters especially in the western part.


Note the missing tracks east of LA5PPA-1 which are due to a 3.5 km long tunnel,
Strømsåstunnelen, between Drammen and Mjøndalen.

13 January, 2016

Magnetospherically ducted echoes in the San Francisco area

On 7. November 2015, several radio amateurs in northern California heard echoes in the 80 meter band. I was made aware of it by Jack, W6FB in Santa Clara, who recorded signals from K6YT some 25 miles away. According to W6FB, the echo effect was also heard north of Sonoma (several hundred miles north of him, reported by N6ZFO).

KM6I, Gordon, in Palo Alto also heard echoes of his own signals and recorded them. In his blog he analyzed the delay from the output of his transceiver and found 157 ms. He found that to be so close to the round-the-world time for signals of 138 ms, that he assumed that to be the cause.

I don't agree, so I took the location of W6FB at locator CM97ah (Santa Clara) as a starting point for computing delay. This is latitude 37.31 and longitude -121.96 and gives a geomagnetic latitude of about 42.5 degrees. Then I put it into my program for computing path length along geomagnetic field lines assuming a height of the reflecting ionosphere on the opposite side of 100 km. The result is shown in the figure and predicts a delay time of 126 ms. My estimate of uncertainty is +/-5 ms.

The delay value is slightly less than 138 ms and easy to confuse with a round-the-world path. The challenge with estimating delays like this from the signal is that amateur transceivers may have an unspecified delay between start of transmission and start of sidetone. Measuring on the audio output as done here, measures the sidetone, not the actual RF.

I discussed this source of error in my 2009 QST article "Magnetospheric ducting as an explanation for delayed 3.5 MHz signals." Therefore the measurement shown above may fit with 138 ms just as well as with 126 ms, it depends on the actual transceiver's delay.

Other properties of the echo, such as the amplitude of the echo which according to W6Fat times was louder than the direct signal, also point to the duct theory as the explanation.

Others have heard such echoes also:
Other posts on the theme: Magnetospherically Ducted Echoes or Medium Delayed Echoes

11 December, 2015

Finally got rid of the pirated USB chips for the UV-5R and the AP510

Both the Baofeng UV-5R handheld UHF/VHF radio and the Sainsonic AP510 APRS tracker come with interface cables with pirated chips. These are clones of Prolific USB/serial chips. Since Prolific has taken measures against this, only old drivers will work with them. That means that one has to stop automatic driver updates as explained on the Miklor site for the Baofeng UV-5R. The same is true for the AP510. This is a nuisance.

I got tired of this and got myself some USB/serial modules from Ebay based on the CP2102 chip instead. The cost was US $1.43 a piece so it should be affordable for anyone. I also got some clear heat shrinkable tube.

19 November, 2015

Curing amnesia in the 10 MHz GPS reference

Just good enough 10 MHz GPS reference with
u blox Neo-7M GPS module to the upper right,
10 MHz output buffer lower right,
USB interface to the upper left,
CR2032 lithium battery center left,
GPS antenna in the center,
and SMA output connector lower left.
My "just good enough 10 MHz GPS reference" which drives the external clock input on my Elecraft K3 kept losing its configuration if power was off for a day or so. I have therefore fitted a CR2032 3V lithium battery as seen to the left in this image.

It is connected in series with a 1N4148 diode in order to prevent attempts at charging the lithium cell. The connection goes to pin 22 (V_BCKP) as described by G4ZFQ on his website. The diode is visible to the upper left of the battery.

With this, I consider the 10 MHz reference to be finished.

Earlier related posts:

02 November, 2015

Radio Ghosts Have Haunted the Airwaves for Nearly a Century

“The starship hypothesis is a very interesting one, and the one which seems to be the most popular one on the internet,” said Sverre Holm, a professor of signal processing at the University of Oslo. “Such theories always excite our imagination, but it builds on a very poor data set. Unfortunately I believe it says more about human imagination than anything else.”

Although scientists have yet to settle on a final explanation for these mysterious echoes, Holm believes this is has less to do with a lack of scientific knowledge than a lack of willpower.

“I think that with today’s satellites and sensors, the mystery of Long Delayed Echoes (LDEs) could probably be solved,” he said. “What’s holding us back is most likely the problem is not considered important enough—it doesn’t occur often enough and doesn’t affect important enough forms of communications.”

These are excerpts from an interview in an article entitled "Radio Ghosts Have Haunted the Airwaves for Nearly a Century" on Motherboard Vice written by Daniel Oberhaus. It builds on a web page that I created some years ago after having spent days studying the archives from the 20's of professor Carl Størmer at the National Library in Oslo.

15 October, 2015

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.

03 October, 2015

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:


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.

11 August, 2015

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?