[PSUBS-MAILIST] coms

Mon Dec 16 20:15:57 EST 2019

Telephone is using low frequency energy, not 150 mhz rf. Big difference in energy loss @ rf, and the higher the frequency the greater the loss.
Low loss coax is rigid, non flexible and expensive. IMO best to put radio inside buoy fiber optic line to sub, no losses, just pulses of light. If your coax lost 3 db per 100', 500' means 15 db loss.
Every 3 db loss drops your power by 1/2!! So a 25 watt radio with 500' of coax = 12.5 watts ( first 100', 3 db), 6.25 watts ( next 100'), 3.12 watts, then 1.56 watts, then .78 watts at the surface. 
Also any received signal is attenuated by 15 db.
Just my 2 cents.
Keith T.K6FEE 
-------- Original message --------From: hank pronk via Personal_Submersibles <personal_submersibles at psubs.org> Date: 12/16/19  4:15 PM  (GMT-08:00) To: Brian Cox via Personal_Submersibles <personal_submersibles at psubs.org> Subject: Re: [PSUBS-MAILIST] coms 

        A telephone can have an 18,000 foot wire, Hank

                    On Monday, December 16, 2019, 4:42:43 PM MST, Brian Cox via Personal_Submersibles <personal_submersibles at psubs.org> wrote:

                Hank,  You would have to use coax, it would just be a matter of what kind.  Or do it like Keith says !  
Brian

--- personal_submersibles at psubs.org wrote:

From: hank pronk via Personal_Submersibles <personal_submersibles at psubs.org>
To: Brian Cox via Personal_Submersibles <personal_submersibles at psubs.org>
Subject: Re: [PSUBS-MAILIST] coms
Date: Mon, 16 Dec 2019 23:19:07 +0000 (UTC)

        Brian,I find Coax to be a bit rigid for this application, I would want the tether to be real soft so to speak.  I tow a poly rope with no issues, in fact the thicker the better.  This is because thicker rope is more buoyant.  I would add a couple small floats to the umbilical.Hank

                    On Monday, December 16, 2019, 3:58:29 PM MST, Brian Cox via Personal_Submersibles <personal_submersibles at psubs.org> wrote:

                David, Jon,    Not sure if it is neutral or not , my guess is that it would be positive.  But there would be a buoy on top in any event.  I don't think the coiling would be an issue as that would tend to cancel out any RF interference ( not that there would be any)  .  You could expect about 2.5 db per 100' i think, so you would want to have enough power to overcome the loss.  You might be able to put a high gain antenna on the floating antenna and or a signal amplifier at the antenna. 
Brian

--- personal_submersibles at psubs.org wrote:

From: Jon Wallace via Personal_Submersibles <personal_submersibles at psubs.org>
To: Jon Wallace via Personal_Submersibles <personal_submersibles at psubs.org>
Subject: Re: [PSUBS-MAILIST] coms
Date: Mon, 16 Dec 2019 21:48:04 +0000 (UTC)

        I think the first thing we need to determine is whether 500 feet of cable is too long for VHF transmission.  Also, what effect coiling of the cable would have since in some situations coils of cable are used as baluns.
Jon

                    On Monday, December 16, 2019, 04:11:01 PM EST, hank pronk via Personal_Submersibles <personal_submersibles at psubs.org> wrote:

        Jon, I was thinking about VHF radio with a 500 plus foot antenna cable to the antenna on the surface.  Then a matching radio on the boat.Don't think smoke will be reliable under water hahaHank

                    On Monday, December 16, 2019, 11:22:19 AM MST, Jon Wallace via Personal_Submersibles <personal_submersibles at psubs.org> wrote:

        More info Hank.  What kind of comms?  Are you wanting to tether ultrasonic comms, some kind of radio like CB, smoke signals?  
Jon

                    On Monday, December 16, 2019, 10:31:45 AM EST, hank pronk via Personal_Submersibles <personal_submersibles at psubs.org> wrote:

        Alan, good plan, but I am sure someone here has ideas.  I am only needing to go 500 feet for my project this summer, so I will start with that and then I can just add to the line as needed.Hank

                    On Monday, December 16, 2019, 7:34:13 AM MST, Alan via Personal_Submersibles <personal_submersibles at psubs.org> wrote:

                Hank,If you don't get a response here, I would join a ROV group & post on one.They would have that stuff down to a fine art.I have searched ROV group information before.How deep are you wanting to go?Alan

On 17/12/2019, at 2:51 AM, hank pronk via Personal_Submersibles <personal_submersibles at psubs.org> wrote:

Hi All,I am in need of guidance.  I want to install coms in E3000 with a tether cable.  I can get 4mm ROV tether at a reasonable cost.  I always tow a buoy anyways.  I need help to figure out how to do this. Hank_______________________________________________
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