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915mhz / 868mhz as a viable frequency for submarines. EmptyWed Apr 24, 2019 1:16 am by merriman

» Pinger 3 - Distance measurement (Triangulation, Transponders and Clocks on Board)
915mhz / 868mhz as a viable frequency for submarines. EmptyTue Apr 23, 2019 2:52 pm by david f

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» John Lambert Plans
915mhz / 868mhz as a viable frequency for submarines. EmptyMon Apr 15, 2019 2:27 pm by david f

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915mhz / 868mhz as a viable frequency for submarines. EmptyMon Apr 15, 2019 2:23 pm by david f

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915mhz / 868mhz as a viable frequency for submarines. EmptyFri Mar 22, 2019 2:37 pm by tsenecal

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    915mhz / 868mhz as a viable frequency for submarines.

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    tsenecal
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    Post  tsenecal on Mon Nov 12, 2018 10:12 pm

    Starting a new thread...

    David and i have a few threads here now on using OpenLRS systems instead of the traditional PPM base frequencies, in an attempt to move submarines into the 21st century.

    Both David and i have found great success in 433mhz in the USA, and 458mhz in the UK.

    There is one small problem with 433mhz in the USA... it requires that you have a HAM radio license to be even close to "legal"...

    There is, however, a different frequency that some OpenLRS makers/sellers have used in the past.  915mhz.  It does not require any additional licensing, and because of that I own a few receivers and one transmitter module that operate using the OpenLRS protocol in 915mhz, and they seem to work okay, as best as can be expected, giving me up to 3 feet of depth in the right circumstances...

    The issue is that no-one now seems to be making these...   my last ebay source has told me that he has moved on to other items for sale, and he will require minimum quantities before he will make more...

    so...

    I have started looking around for other 915mhz equipment.

    By shear luck, a very large Chinese radio manufacturer, FrSky, has started producing a range of products using 915mhz.  they sell it as a long range option for drone flyers... with quoted distances of up to 20km by some reviewers (air usage).   again, what i have discovered is that i can get anywhere from 18" to 36" below the surface and still have excellent control of the submarine using 915mhz.

    I have spent the last 3 months testing both the 7 channel receivers that use OpenLRS on 915mhz, and two of the FrSky recievers that use the 915mhz frequency.

    The modules i have tested are the OpenLRS TX module and a separate 7 channel RX that was sold by a russian ebay seller,

    I have also been testing the FrSky R9M module, and both their R9 receiver, a full size 8 channel receiver, and their R9 Slim, a small 6 channel receiver designed for drones.  I also just recently picked up a brand new receiver they sell, the R9 mm/mini.  an ultra micro 4 channel receiver designed for tiny racing drones.

    I have tested both the R9 and R9 slim in my Norbert Brüggen Delta submarine, and the R9 slim in my SWM blueback.  i have just recently put the R9 mm in to the blueback, and will be testing it as soon as possible.

    to give you an idea of how big the R9 mm is, i have attached a photo.

    the R9 slim and R9 mm are not designed to attach directly to servos without a little extra work, they are primarily designed to connect to flight controllers for drones with only 3 wires (positive, negative, signal) and they can operate on a single lipo cell (3.7v), but with a little work (soldering up connectors or a harness) they can be made to work with standard size or miniature servos.

    more to come.


    915mhz / 868mhz as a viable frequency for submarines. Frsky_11
    david f
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    Post  david f on Sat Dec 08, 2018 11:21 am

    Impressively tiny equipment there, Tim!

    Could be very handy for conversions of small kits.

    The problem with all these developments is the continuing manufacture of equipment. 433Mhz seems to be reasonably robust in supply but I note the difficulties that you have in using 433 Mhz in the US and the supply problem with 915 Mhz.

    To help anyone wanting to experiment with 915Mhz in the UK, I have just been having another look at potential UK radio frequencies. (Better than writing Christmas cards!) It seems that 886-906Mhz would be possible if you can tolerate some interference from industrial, scientific and medical apparatus (ISM).

    This is the current basic document covering radio control:

    https://www.ofcom.org.uk/spectrum/radio-spectrum-and-the-law/licence-exempt-radio-use/licence-exempt-devices/Radio-controlled-models

    This document states the following:

    "In addition to the frequencies above, radio control models may also share the frequency bands allocated to General Non-Specific Short Range Devices with all other such applications. Most of the Non-Specific Short Range Devices allocations remain impractical for model control, due to restrictions on channel capability or too little power to give sufficient range. Also, most General Non-Specific Short Range Devices allocations are located in bands also used for industrial, scientific and medical apparatus (ISM), so may suffer from interference in certain locations. Details of ISM bands are shown in annex A of the UK Frequency Allocation Table."

    Annex A states:

    https://www.ofcom.org.uk/__data/assets/pdf_file/0022/103297/fat-ism-frequencies.pdf

    "83·996-84·004 MHz
    167·992-168·008 MHz
    886-906 MHz (My emphasis)

    Radiocommunication services must
    accept harmful interference from ISM
    apparatus operating in accordance with
    the WT (Control of Interference from
    RF Heating Apparatus) Regulations
    1971.

    The WT (Control of Interference
    from RF Heating Apparatus)
    Regulations 1971 specify the limits
    of levels of radiation permitted
    outside the ISM bands."

    So could be worth some experiments?!

    David
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    Post  tsenecal on Sun Dec 09, 2018 3:48 am

    David,

    i have specifically standardized on this hardware because it is backed by one of the larger manufacturers... it is not open source DIY equipment. it is commercial equipment sold by FrSky to be used with FrSky radios, the target market is quad copter pilots. It is sold in the 915mhz range for US sales, and 868mhz range for European sales.

    I am at a R/C regatta/fun-run this weekend where i had hoped to be testing the receiver shown in the original posting, but the speed control for that submarine died 15 minutes into the first day of the fun-run, and i wasn't able to do any real testing. It's getting too cold where i live to be running anything (water is now solid) so i am going to have to pick this testing up in a few months when the ice melts.

    beyond that, i have tested standard size receivers and mid size receivers and they are performing nicely.
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    Post  david f on Thu Jan 03, 2019 1:41 pm

    Thanks Tim. I had rather missed the point that the gear is being offered by a major manufacture (FrSky) so hence better reliability of supply?

    It must have been something to do with Santa Claus but just before Christmas, Hobbyking were offering this combo below at the bargain price of £3.95

    ORANGE RX OPENLRSNG 915MHZ WITH BLUETOOTH TX MODULE AND RECEIVER COMBO (JR PIN CONFIGURATION)

    SKU: 9171000872-0


    I duly ordered one and when (and if?) it arrives I will give some feedback on how it is. (I am particularly interested in the use of Bluetooth for setup and whether the frequency can be changed to UK frequencies.)

    David
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    Post  tsenecal on Fri Jan 04, 2019 3:21 am

    David,

    so sad to see that last post...

    2 huge problems:

    1) I bought that when it was brand new... at the time i think it was a package deal for $50 or so... but it was a total bust. it is running (like all things OrangeRX) an outdated rev of the firmware... but it is a SPECIAL version of the firmware designed to work in conjunction with a mavlink drone flight controller. it requires a special version of the Chrome Configurator, and even then, there are no binaries available for the 915mhz chipset. i actually destroyed a receiver trying to update it with the standard configurator and original 915mhz binaries. when i got the second receiver in, i was able to get it working (only with the special 915mhz bluetooth module) but even then, i had to buy a ppm to pwm converter to get standard servos to work with the receiver. as i said, the receiver is designed to work with a flight controller, not servos, so it literally has a 3 pin connector to go directly into one of those, and the decoder allows you to revert back to servos.

    link to sbus/ppm decoder:
    https://alofthobbies.com/frsky-sbus-decoder.html

    link to sbus/ppm decoder programmer:
    https://alofthobbies.com/frsky-servo-channel-changer-sbus-cppm.html

    if you need more than four servos, then you will need to have 2 or more decoders, in parallel, up to a total of four decoders for 16 servos.

    then i had to wire up a wiring harness that fed 6 volts to both the receiver, and the decoders, to drive the servos. it was a dreadful mess of wires.


    2) 915mhz is not legal in Britain, 868mhz is... and for the openlrs/openlrsng devices, the 915mhz chips are pushed a little too far to work right, so a different set of chips specifically for 868mhz need to be supstituted 90% of the time.


    put lets hope you have better luck... right?


    all in all, even with the 915mhz being legal, it still ended up being a total bust.
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    Post  david f on Fri Jan 04, 2019 8:45 am

    Fortunately it only cost £3.95 - not too many dollars even with current exchange rates!

    Your experiences, Tim, maybe show that they were offloading the stuff. (I was getting worried that Hobbyking were deliberately targeting me with special offers!)

    Did your version of the combo have Bluetooth?

    Many thanks for the advice.

    David
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    Post  tsenecal on Fri Jan 04, 2019 7:11 pm

    David,

    my combo had the bluetooth, but i had to remove it... the bluetooth board connects to the exact same pins the FTDI adapter connects to when connecting the TX module to the PC when running the Configurator chrome app... I didn't want or need the bluetooth, so it was removed as soon as i discovered that i needed to. of course, i then promptly fubar-ed everything trying to update the firmware, and the bluetooth was irrelevant at that time.

    I have no idea how/what/when the bluetooth is used in the originally intended mavlink scenario.
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    Post  tsenecal on Sat Jan 05, 2019 11:40 pm

    one other "advantage" i neglected to mention in the first thread... because the new FrSky 915mhz R9 equipment is made by FrSky... I don't have to build my own telemetry devices (unless i want to) all the OEM X series sensors plug directly into the receiver, and the transmitter knows how to display the data with no futzing.
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    Post  david f on Sat Jan 12, 2019 2:27 pm

    Well the good news is that Hobbyking delivered the previously discussed equipment very quickly. The bad news is that it is exactly as you say, Tim!

    No servo sockets etc.

    I had a little play with the Bluetooth and this did pair with my Samsung Mobile which had"Mission Planner" installed but for any serious configuration I would need a laptop with Bluetooth.

    My experiments were conducted quickly because I had no way to change frequency.

    So I don't suggest anyone else repeats the experience although I now have an interesting £3.95 paper weight!

    915mhz / 868mhz as a viable frequency for submarines. 20190111

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