Your foreign license plate number?

For any amateur band above 20m this is the easiest solution in the field, a 5 meter whip antenna with a magnetic suction mount on the trunk of your car, it results in a SWR of 1.6 and you can tune it to anything above 20m by simply shortening the whip. MFJ makes these, the MFJ 1979 is the whip and the MFJ 336T is their magnetic suction mount. I haven’t tried this on the roof yet since I’m slightly worried about the thickness and the lack of anything that provides more stiffness. After posting these images on facebook the first reaction of my cousin was, are you now also carrying foreign license plate numbers? I rest my case about opinions in our country.

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The MFJ 1979 and their 336T on the trunk of my car
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The analyzer shows a SWR of 1.63, so that appears to be fine
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16-Mar-2017, a field afternoon, the FT-991 was able to tune the whip between 14250 and 14350 kHz, I’m deliberating about a solution to move it more center 20m band.
Fieldday on March the 19th, notice the tuning stub at the end of the whip. Also, what you don’t see is that I added several radials to the magnetic suction mount. 3 radials of 10 meter each did the job.
It turns out that a 25cm tuning stub centers the resonance frequency in the 20m band.

 

Last update: 17-mar-2017

Lowrider WSPR

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WSPR on 474 kHz
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WSPR on 136 kHz

WSPR on LF and MF at respectively 136 kHz and 474 kHz. I listened with my loop antenna and was able to pick up a few stations, MF (11 stations seen) was easier than LF (4 stations seen). On LF there are two strong digital signals near the narrow band that we are interested in. One problem to solve is the frequency stability of the SDR. The airspy LO is somewhat temperature compensated, but it tends to drift. but there is a possibility to connect it to a frequency reference. I’m not sure how amateurs make an transmit antenna for these frequencies, that could be a challenge.

Lowriders are also cars.

Quadcopter

Although most people probably call it the D-word hobbyists don’t, because they don’t want to be associated with the D-word. I made one last summer, it takes a couple of days and gradually you get something you like, and what you’re able to control safely.

 

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This is the DJI F450

 

 

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PMU of the quadcopter

 

 

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RC controller set-up

 

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You do need some 5 or more amps to charge the batteries, so there is a dedicated charger

And finally, add the gimbal, what is a gimbal? It keeps the camera straight, stable, whatever. And you add of course controls on the transmitter to adjust the gimbal remotely. Add a video transmitter, and you’re done.

Next, wait for a nice day without too much wind (4 m/s is really a lot already, maybe 8 m/s is the limit) go in the field and enjoy, just browse the internet to find out what’s possible, and also, where it is allowed. Here are some of the videos that I made:

 

 

 

Could we live without a leap second?

Before the atom second was introduced timekeeping was based on measuring the length of day by astronomic measurements. The rotation speed of the Earth averaged over a long enough period of time resulted eventually in the number of oscillations between two hyper-fine states of the Caesium atom which was used in the atomic clock invented in 1955. As a result presently 9,192,631,770 counts between the ground states of Caesium define the second, see also [ref]

At the same time another problem occurred, namely that there are ‘users’ who want an atomic time system that runs with the rate of the atomic clock but that does not deviate more than a second from Earth rotation time. This time system is called UTC, and in order to maintain UTC we need leap seconds so that the difference between UT1 (Earth rotation time) and UTC (the coordinated universal time based on the atom clock) does not grow to more than 1 second. Tonight at 0:00 UTC (July 1st 2015) a leap second is introduced for this purpose, but the question is, do we really need this? Could we not live with atomic time, and still keep in pace with Earth rotation without introducing anomalous seconds. The answer to this question is yes, but it would call for a different definition of UTC.

To understand this concept I plot below the difference between UT1 (Earth rotation time) and TAI (the atomic clock). The difference between both time systems is shown in milliseconds; it shows a long periodic trend that can be well described by a polynomial function over the past 50 years, the second plot shows the difference between an optimal fitting parabolic trend function. The analysis shows that there is no difference larger than 1000 milliseconds (except in the early part) which would fulfill the requirement that a coordinated time, UTC, could also be constructed as a continuous function.

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Eventually the definition of the atomic second is affected by the choice to count the number of oscillations between two ground states. The current length of the atomic second was ‘conceived’ by a committee who looked at a couple of years of data in the sixties and seventies when Earth rotation was slightly different compared to 2015. If you would re-calibrate the atomic second according to the parabolic function then we wouldn’t need the leap second. Another alternative would be to allow for a larger difference between UT1 and TAI, and to simply scale the atom second to a new value.

So the answer is, yes we could live without the leap second if 1) a suitable parabolic correction function was used, 2) or if the atomic second was re-scaled and larger differences were allowed.

Last update: 30-jun-2015