Hello Stefan,

Such a coincidence; I recently put a similar LiFePO battery on my wish list.

I think that the ~ 3 kWh LiFePO batteries might last over 500 deep cycles (some claims up to 2000 deep cycles) if charge/discharge conditions (including temperature and rates) and battery specification match reasonably. At 1000 deep cycles that might be ~ $1.50 per 3 kWh cycle (less than the round-trip fuel cost driving to/from the test location).

I’m planning to obtain cycle-life data from a battery custom-packaging company or battery-cell manufacturing company before selecting an LiFePO battery and buying. They don’t like to publish the data because they can’t guarantee it, but they have a lot of data. Some lithium batteries can (practically speaking) provide ~ 3 times as much energy throughput (total energy before end of life), if they are used in a way that manufacturer/custom-packager cycle-life data would suggest. I’m hoping that with such manufacturer/packager data a 3 kWh battery can be specified, selected and operated in a way that provides over 1000 deep cycles.

For maximum energy throughput (total energy before end of life) from lithium batteries I usually try to match (before selection/purchase, and during use): (a) operating conditions and (b) manufacturer/custom-packager battery-life data, for the following:

Charge ambient temperature, discharge ambient temperature, charge rate, discharge rate, discharge depth (DOD), and DOD during storage.

I think that LiFePO might be more tolerant than some other lithium types for some of the above parameters.

Selection and operation to optimize for the 6 factors above can provide 2x to 3x greater energy throughput (than with typical selection and use) for many types of lithium batteries; hoping it helps for LiFePO.  

Sometimes with lithium batteries I also optimize for other parameters, like:

(a) max charge (not charging to 100%, based on manufacturer/custom-packager life specifications)

(b) charge profile (custom current-vs-time-and-voltage, using a custom charger, based on manufacturer/custom-packager life specifications)

These two can also significantly increase energy throughput, but they require more effort for less benefit than the six factors in the preceding paragraph, so I usually don’t bother with these last two parameters.

Hope your power supply preparations go well.

I have a good power supply and amplifier for earth loop, and accessible guard rails, and accessible good soil, but the accessible guard rails are nowhere near the good soil :-(

Your spectrograms look excellent. Suitable for framing for 2 kHz earth loop far field; very nice images.

73,

Jim AA5BW

Hi Jim,

yes, i bet that 970 Hz will be possible without much trouble. Today i continued with some next preparations: Some years ago i built a DC power supply from '12 V' to 0...150 V. It is capable to manage 500W, at least i think so :-) I made a short test at 180 W output power and measured/calculated 84 % efficiency. Since i learned a bit more since the time i constructed it, i think i can even rise the efficiency by replacing a MOSFET...

Also i consider to invest in the future and buy something like this: https://www.robur-akku.de/ Quite expensive but others buy a 'FT897' or 'TS-2000' or 'IC-756' or such stuff :-)
The 48 V / 60 Ah version contains about 3 kWh so it would be no problem to drive a 1 kW PA for 2 hours (or even 2 kW for 1 hour!) at a good efficiency and without a loud, inefficient and stinking generator that doesn't manage dynamic power changes...
The modern world!

At least, the next idea is to build a H bridge running at 0...150V. It should allow to manage the next 3 dB power step at least. And the circuit design will be such that i can go down to ELF (the real ELF, 3...30 Hz). A discrete tank circuit should prevent from harmonic radiation. I will make measurements showing the signal in the frequency domain then ;-)

73, Stefan


Am 06.08.2018 20:40, schrieb [email protected]:

Stefan,

Congratulations on 2470 Hz and 1970 Hz (ULF) far-field records!

A remarkable step from inverted-L efforts below 3 KHz last year; high SNR in 40 minutes at 2x far field on (if memory serves) the first attempt after your trial run.

Interesting that your 2470 Hz and 1970 Hz results were somewhat similar in this variable-propagation region (2kHz-4kHz 100km-1000km). Could that mean good things for lower frequencies? Perhaps most of your E-field is vertically polarized with this loop; I wonder if that will provide more stable propagation in this region.

Thanks for pushing the boundaries again.

73,

Jim AA5BW

Hi ULF,

On Sunday, 5th 2018 i successfully crossed the far field border on 2470 Hz for the first time. That's the 121 km band. Later i even crossed it on 1970 Hz, the 152 km band. These are two new records of the lowest frequency signals generated by amateurs and received in the far field. The distance between RX and TX was 55.6 km . The far field for 2470 Hz starts at 19.4 km distance. For 1970 Hz it starts at 24.3 km distance. The RX antenna and the TX antennas were loops!

By running about 100 W (PA DC input) i managed to get 910 mA antenna current on 2470 Hz into the earth loop in JN39WI. Here i transmitted a plain carrier from 06:13...07:15 UTC.
Later i QSYed to 1970 Hz and here i got 910 mA as well. The 1970 Hz transmission took place from 07:19...08:21 UTC.

Despite beeing in the middle of a large forest there was good internet connectivity and so i was able so watch my own grabber window showing the band activity on 2470 Hz in a spectrogram of 424 uHz FFT bin width, which is very wide for that frequency range! The spectrogram uses a Hann window and the FFT window time is about 40 minutes, so it took some time until a peak builts up. But already after 20 minutes i saw that something happens! After 40 minutes the carrier transmission reached an SNR of about 20 dB! It was a relatively quiet morning for early August.
All the VLF stream data is stored into a ~ 12 day covering buffer so i have the chance to optimise the filter settings and antenna mixing in a postprocessing to achieve the best SNR from the system.

For the 1970 Hz transmission there was no spectrogram available but since i had internet access and a Linux notebook available, i processed the VLF stream data (via SSH remote access to the storage PC) during the transmission and followed the peak's SNR building up!

It clearly looks like this antenna outperforms my large inverted L in 30 m above the ground, at least into the ULF range! This opens up a new room for experimentation on the way down to DC! :-) Now i need to get rid of these output transformers since they will become problematic for wide-band experimentation on ULF / SLF.

Now, attached you can find two images showing spectrum peaks from the two bands, out of the 55.6 km distance. The complete transmission time is here integrated in one peak. Since the carrier S/N can also be calculated from decoding a '*' message in EbNaut, i also show the results for such calculation along with the whole postprocessing chain.

Spectrograms will be produced as well, but this will take a few hours here...

73, Stefan