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

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

    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.


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    david f
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    Re: 915mhz / 868mhz as a viable frequency for submarines.

    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

    tsenecal
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    Re: 915mhz / 868mhz as a viable frequency for submarines.

    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.

      Current date/time is Wed Dec 19, 2018 11:11 am