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[Tim Logan]

Is there any reason a Taranus 2019XD with the R9 900mHz module would NOT make a good submarine radio? I am aware of the depth limitation being in the 4 to 6 foot range. That is not an issue to me.
   My understanding is that the sub would be running constantly on 900 MHz whether submerged or on the surface because switching between frequencies is done manually at the transmitter. (ie not redundant). For this reason I’m wondering if there’s any limitation to using 900 MHz on the surface? The only other limitation I can think of would be the battery power which would depend on how many mW you’re sending out at 900mHz. The module itself does have the ability to have an external battery hooked up.[/size]i’m trying to decide if the R9 will suffice or if I need to bite the bullet and go for the FrSky X18 tandem. Thank you in advance for any input.[/color]

[Umi_Ryuzuki]

I don't think its a good idea to use 900mhz.
For surface running no issues, but as soon as you submerge any distance away from the model, you may lose signal.
 
https://www.youtube.com/watch?v=hGDxRDqIfdk

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[rhavrane]

Bonjour Tim,
I agree with Umi_Ryuzuki, I have had the opportunity to meet several model submariners (see my videos) and the "best / less bad" frequency which should be used is 27 MHZ then 41 MHZ. Above, no transmission underwater.
Example : https://youtu.be/MyWzYXgae_c

[Tim Logan]

Umi and Raphael - thank you. The use of 900mHz in tandem with 2.4 has been tested quite a bit in the US sub community and accepted. Normal operating distance (with 2.4) and submerged 4 - 6’ (with 900) works just fine. Most sub drivers are totally happy with that as it is rather fool hardy to seek greater depths. So that part I am not worried about. What I don’t know is if 900 (without a tandem freq) on the surface has any limitations.
  The ideal of  course (both cost wise and operationally) would be 75mHz. However, finding good clean 75mHz systems is like pulling hen’s teeth - just very difficult to find. If I could find one, that would be my choice. If you know of a source in the US, that would be great!!! Thanks again.

[JimG]

There should be no problem using the 900MHz module for both surface and submerged. 900 MHz will have a longer range than the 2.4 GHz for the same transmitted power and is less affected by water absorption. Many long distance fliers use the 900 MHz band for their planes due to the much longer range. (Ignoring the legality or not of flying out of sight)
Jim

[Tim Logan]

There should be no problem using the 900MHz module for both surface and submerged. 900 MHz will have a longer range than the 2.4 GHz for the same transmitted power and is less affected by water absorption. Many long distance fliers use the 900 MHz band for their planes due to the much longer range. (Ignoring the legality or not of flying out of sight)
Jim

Thanks Jim - that’s what I needed 

[tsenecal]

I have been using 900mhz for ALL my subs since about 2017

I currently use ExpressLRS modules for most, but i have tested:

Frsky ACCST r9
Frsky ACCESS r9
ExpressLRS 900mhz
TBS Crossfire 900mhz
OpenLRSng 900mhz
Futaba TM-18 900mhz

I have even "successfully" forced Jeti 900mhz backup to work.

All have worked reasonably well.


for more info on this topic:
https://www.theassociationofmodelsubmariners.com/t1842-868-915-mhz-as-a-viable-frequency-for-submarines


Regarding OPs original question regarding the 2019 ACCESS taranis x9d with an r9 receiver, I specifically tested the Frsky Qx7, with the 2019 ACCESS R9 module, with the Frsky ACCESS R9 SX six channel receiver.  My x9d is the older ACCST model, but the 2019 Qx7 and x9d are identical in functionality when using the 2019 ACCESS R9 module.

One of the nice features of all the Frsky radios is that all the ACCESS models support the independent use of R9, including the Tandem models with their internal 900mhz rf deck.  I also have a Frsky x20 Tandem, and it will work with the same r9 sx receiver with out needing an external 900mhz module.

[Tim Logan]

Tsenecal -
  That’s great feedback. Thank you. What output wattage  are using with 900mHz? My understanding is that you need to up the wattage output if your submersing up to 4’ or so. And if so, have you had to supplement your radio’s battery? Thank you again!!