Welcome to your 900Mhz Dipole Antenna!

[QuarterMaster]

ALCON,

Spoke with KMc earlier on the "antenna" question. (Bet you didn't know there was one!).

It's our hope to "crack the nut" with respect to range/running depth, limiting output power (extend TX battery life) and simplifying the install. Kevin is plugging along researching this as well.

An interesting article on our new antennas. Might be a tad more difficult, but not insurmountable. How to Mount/Position Transmitter and Receiver Antenna on FPV Drone

I see we need to mount them vertically, not horizontally. Also using an external dipole on the TX (HOURUS vs X18/X20) and actually aligning in the direction you face will appear to help as well. Which a lot of people would do with the 75Mhz when they appear to have lost signal. Pointing it directly at the boat was bad, the radiation pattern of the monopole antennas should have you pointing them to Jesus as it's perpendicular to the antenna.

We need more crowd research here!

Mmmmmmm.....donuts!

[Das Boot]

Did you get your transmission fixed or buy a new truck?

[Nathan]

Ed, how are you dealing with the confined vertical space normally found in a WTC? I don't believe curving the antenna is a good idea, but even a good sized cylinder is probably shorter in the diameter than the dipole is long.

[QuarterMaster]

Ed, how are you dealing with the confined vertical space normally found in a WTC? I don't believe curving the antenna is a good idea, but even a good sized cylinder is probably shorter in the diameter than the dipole is long.

Think "outside the box".

Bob did.

[RCSubGuy]

Logan and I are going to perform a test regarding antenna placement today (if I can find the time). We'll film the process and post up the results.
News at 11!

[QuarterMaster]

To catch everyone else up on what Bob is doing after he and I were discussing due to an "Email Thread" started by Steve O'Connell.

What follows I've pulled from that email.

So before any of you respond...

1:I understand I AM NOT an RF or Antenna Engineer of any sort.
2. The following is merely MY interpretation of radiation patterns and how they appear to interact based on what I've taken the time to research.

'scuse the "Eddiegrams"

Such as I enjoy writing, this is a non-text discussion lol! Too many keystrokes can follow! But I'll at least say this...

Two main points to think about:

1-How much "more" performance is warranted? for 80% of the users, good enough works. Especially when you take into account the percentage of runtime in "clear" water supporting constant "at depth" running.

2-Basically it's a guideline, something to strive for, not obsess over. It's just good to be aware of it.

For the record, The Krick's 900Mhz antenna is laying horizontal, bent in a "crescent" shape! This past weekend at Fitz's Fun Float, Bob noticed my TX was set to the lowest TX power setting of 10mW!! I had been running for close to an hour with degradation only occurring when I dove > than its body length and that was 20' out, and it only gave loss of telemetry warnings while still operational so I didn't even know it. Bumped it up to 100mW to see any difference. Then Bob stole it from me and then attempted to own me by almost mastering a dynamic diver running at a consistent PD. Grrrrrr Bob!

BTW, as I bench test at 10mW (which I did a couple of days earlier) to not saturate or harm the RX, I need to add checking TX output power in the checklist!





The 900Mhz antenna in the X18/X20: So the emission "donut" wave pattern is perpendicular to the long axis of the handle. So if you're holding the TX between you and the boat as one normally does, and have the aforementioned long axis at right angles of the imaginary line to the boat, the "donut" is radiating at YOU and the boat up to the sky and down to the ground. As long as you're pointing that handle side to the boat, you're keeping it WITHIN the imaginary tire whose center is at the handle while pointing at you and the boat right angle to the horizon.

From my understanding of what I've been researching anyway.

Graphically represented like this...

The donut radiating from the TX naturally held pointed at the boat. You're at "Y", the long axis of the handle is represented by the "X" axis through the center of the donut. So the target boat is within the maximum radiation output of the TX. So would a drone be at 45 deg up or directly above you! For the record, this is in opposition to our 75 Mhz radios whose radiation donut is at right angle to this. Pointing those antennas at the boat as I've seen so many do is bad! Best way for those of course is keep the antenna pointed at the sky!



Here is what the dipole antenna would best "see" from the boat's perspective, if placed optimally. The boat has now good possible reception across the horizon in any direction she's headed. The next best thing would be to angle it 45 deg or so. If laid flat along the long axis of the hull, it would match the TX pattern and would see best athwartships, when she's running at right angles to you.





A good way to visualize best pattern matching as if the two "donut's" were two joined "links in a chain". TX vertical, RX horizontal.




The point being for best performance, sorta point the handle (top of the TX) in the direction of the boat. While one should orient the RX antenna as best as one can, it's NOT a deal breaker and we'll no doubt see this proven over time. If you turn in place bringing the boat off in either shoulder direction, you have the least performance. The nice thing is as long as the handle (screen end) is pointed toward the boat you can hold it vertically or horizontally. It probably doesn't help to be like me gesticulating like a madman when speaking. No, don't be an "Ed".




ALL RF Engineers I've worked with told me "FM" stands for "F#¢%ing Magic".

Again this is my understanding from what I've learned so far, and seems to make "sense". We'll learn more over time.

Now everyone is caught up, let's see what Logan and Bob discover.

As for me, I'm one with the "donut".

[RCSubGuy]

Testing complete. Working on the video now. REALLY interesting findings, people.

[RCSubGuy]

Video will post up later today as part of my weekly update, but here are the results. Really interesting results.

Our testing methodology involved the creation of a watertight enclosure that would allow for orientation of the dipole antenna underwater in relation to the transmitter. Testing equipment included a FrSky X18 Tandem radio paired to a TDR10 Tandem receiver. Output power was set at 250mW of a possible 1W (25%).

Two test series were conducted, one with the watertight box in about 18" of water behind a concrete lip in my pool spa. Interested in seeing how much the concrete affected signal strength, we conducted a second series with clear line of sight between the RX and TX. Due to constraints of my yard, the first tests were conducted at a distance of approximately 80ft from the receiver, and the second set was at about 40ft. We used the relative signal strength telemetry read at the transmitter (a built in feature of these radios), which is a value between 0 (no signal) and 100 (full signal strength) to get the following data:


RX in spa behind a 16" thick concrete/stone berm - 18" water depth - 80ft distance:

Description	Antenna aligned to TX	Antenna 90deg to TX	Antenna 45deg to TX	Antenna Vertically aligned
RX in open air	90	95	100	100
RX submerged	40	38	37	43
TX facing 90deg to RX	0	0	0	36

RX in pool with clear line of sight to TX - 24" water depth - 40ft distance:

Description	Antenna aligned to TX	Antenna 90deg to TX	Antenna 45deg to TX	Antenna Vertically aligned
RX in open air	95	100	100	100
RX submerged	40	45	46	50
TX facing 90deg to RX	0	39	37	40

Takeaways:

1. I don't see a significant difference in signal strength based upon the orientation of the receiver dipole antenna and the transmitter
2. There is a significant reduction in signal strength when the transmitter is not operated facing directly toward the receiver
3. There may be a large difference in signal strength when the distance between the TX and RX is increased far beyond the constraints of my test environment for this experiment, however, in my experience, most RC sub skippers operate their subs at a distance within 80ft from themselves. Any further out, and submerged operation becomes problematic and/or foolhardy. Operation while surfaced means that the built in 2.4ghz antennas are in play, and vast distances are achievable with high signal strength
   
   SO
4. When setting up the antenna in your sub, align the 900mhz dipole antenna vertically if you can.
5. If you cannot align the antenna vertically, avoid operation of your sub with the antenna aligned with your position

BEST:



GOOD:


NOT IDEAL:

[Nathan]

Sounds like we need a way to extend the antenna outside the WTC with a waterproof connector. Any ideas on where to start to source such a thing? What are these connectors and cables called?

[QuarterMaster]

Sounds like we need a way to extend the antenna outside the WTC with a waterproof connector. Any ideas on where to start to source such a thing? What are these connectors and cables called?

Nathan, I think your missing the point of Bob's test. Depending on your needs, there may be NO NEED to do anything like that. If you spend 90% of your time at PD in our Texas mud, which I suspect you do, "GOOD" will work for you. Read Takeaway #4. Even at that beautiful Sylvan Rodriguez Park, you really can only run at depth 20-30 ft out before feeling "concerned".

So unless you have ALVIN and like to explore the depths of your swimming pool, or local quarry, or Cohutta/Carmel (1 weekend a year). OR you run below PD > 80' away (GFLWT) you need not penetrate the hull with 900Mhz. 2.4 is a different story.

Who out here wants another hull penetration to "feed"?

Look, it's about performance, what you need vs what you want. In my not so humble opinion, in a WTC you need to mount the RX near a BH anyway unless you purchase a custom IPx connector. Why do that unless you REALLY need to. I have a paycheck that states 80% of the users out there either don't care, or their needs don't warrant that.

I've been repeating the above long enough now (what are YOUR requirements??), so for those who care, read this....

In fact BOOK MARK it.

How to Mount/Position Transmitter and Receiver Antenna on FPV Drone

That being read, my recommendations are (for 80% of you).
Or go ahead and pop a hole offering another potential leak point.



I have spoken.

[Nathan]

I definitely get what you are saying, Ed, and you are right that most of the time alignment within the cylinder will be just fine. The angle within the cylinder idea is very good, but still not always possible. And then the sail and periscopes just sit there staring at you... And as you said, people may have a requirement for a vertical placement - a search on "IPEX 4" got me some results on Amazon, if anyone needs to go that route.

Nathan

[redboat219]

How about disguising the antennae as one of the mast?

[Nathan]

How about disguising the antennae as one of the mast?

That is exactly what I was contemplating

[QuarterMaster]

That is exactly what I was contemplating

GFL making it reach! Boy I wanna see that!

Now REREAD Bobs analysis!

But feel free to make extra work for yourself with an additional point of failure for 5-10% increase!

FWIW. no worries on anymore comments from me, I'm done here. Moving away from this subject at A/A Flank. Ping away boys!!

[rwtdiver]

For me, its 75 Mhz, if I can find them, and if not, 2.4 all the way. Just do not need all that tech stuff to run submarines. But, if that is your cup of tea, coffee, coke, or what ever. Go for it!

Rob
"Firemen can stand the heat."