[PSUBS-MAILIST] coms

Mon Dec 16 22:10:34 EST 2019

 Yes, an interface is required.  Looks like such devices are manufactured but I haven't found a price for them yet.  Unfortunately VHF cannot be easily modified.  Using conventional means, your radios are going to require 50 ohm cable, shielded, to have a proper standing wave.  You can find lots of information online about standing waves and how the RF energy flows around the coax cable by searching "how to build a vhf antenna" or "marine band antenna".  Receiving is one thing, but transmission is quite inflexible regarding electromagnetic laws of science.  The risk is is burning out the transmitter.
Keith is correct about the signal loss over 500 feet.  I found a couple of resources (see links below) that shows a max length of 140 feet for VHF using RG8u or LMR-400.  It's a big cable at 10+mm in diameter and the max length equates to about a 3db loss, which makes sense since I believe a half-wave dipole provides a 3db gain.  So the cable loss cancels the gain of the antenna.
http://www.rfcoaxconnectors.com/technical-coax-cable-length-choice.phphttp://www.rfcafe.com/references/electrical/coax-chart.htm
I have a feeling the RF to Fiber converters are not cheap since I can only find "request a quote" pricing online although I haven't done an exhaustive search for a supplier.
Maybe older technology is appropriate here.  A phone-like "intercom" between sub and surface, converted to radio at the surface?

Jon

    On Monday, December 16, 2019, 09:15:11 PM EST, k6fee via Personal_Submersibles <personal_submersibles at psubs.org> wrote:  

 Some kind of interface would be needed to convert from optical to analog signals into the radio. I haven't thought along these lines before, so no investigation into what is needed.
Could use a router with fiber input and bluetooth out to a bluetooth capable radio. Maybe a simpler way have to see what's available.
Keith T.K6FEE 
-------- Original message --------From: Brian Cox via Personal_Submersibles <personal_submersibles at psubs.org> Date: 12/16/19 5:33 PM (GMT-08:00) To: Personal Submersibles General Discussion <personal_submersibles at psubs.org> Subject: Re: [PSUBS-MAILIST] coms 
Keith,    Is the fiber optic line linked to a control unit that networks to the radio?    Would you need a computer controlled radio?
Brian

--- personal_submersibles at psubs.org wrote:

From: k6fee via Personal_Submersibles <personal_submersibles at psubs.org>
To: Personal Submersibles General Discussion <personal_submersibles at psubs.org>
Subject: Re: [PSUBS-MAILIST] coms
Date: Mon, 16 Dec 2019 17:15:57 -0800

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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