2.4 GHz Antenna Routing

[Surcouf]

I have been on this forum for awhile, learning as much as I can, but this is my first post. I am in the process of putting together a Victoria class submarine 3D printed from the files Bob sells on the website. I have purchased the 70mm R&R WTC, and had Bob install a forward servo.

My question relates to receiver placement and routing of the 2.4 GHz antenna coax. I have an FrSky X18, and a TD R10 receiver. I purchased the 2.4 GHz antenna extension kit from Bob as well. The receiver will only fit in the battery compartment. However, this raises the question of where to route the antenna. If I have it penetrate the forward endcap, then it is easy to route, but causes issues with disassembly of the WTC for post mission and maintenance since the core of the cylinder is attached to the aft endcap. Routing the antenna through the center tube to the aft endcap, I would imagine will cause issues in that it is parallel and in close proximity with the power and servo wires (unless the shielding does a better job than I am expecting). I have seen low frequency radio antennas routed on the outside of the ballast tank, by notching the ballast tank bulkheads, but those antennas were smaller in diameter. Also, not sure if the antenna extension is long enough to reach the aft endcap, forward again sufficiently to reach the top of the sail hidden as a mast or periscope.

I apologize if I have missed posts related to this specific question. I would appreciate any insight.

Thank you.

Tony

[RCSubGuy]

The antenna extension should be plenty long enough to get down the central wire conduit and out the back of the boat. Your interference concern is valid, however. Both power and servo wires will be sharing a very enclosed space. The coax portion of a 2.4 GHz receiver antenna does a good job of shielding the signal conductor from nearby electrical noise. It is generally not very vulnerable to interference from your power wires and servo leads.

[Timothy L]

This was s good question - thank you for posting Tony. Bob - do you have photos of how your tandem antenna and receiver are installed in an R&R cylinder? That would be very helpful. Thank you.
Tim (another newbie)

[Surcouf]

Bob,

Thank you for the information. I am glad to know that this is a viable way to route the antenna to make maintenance easier on the cylinder.

[RCSubGuy]

This was s good question - thank you for posting Tony. Bob - do you have photos of how your tandem antenna and receiver are installed in an R&R cylinder? That would be very helpful. Thank you.
Tim (another newbie)

No, I don't. I don't think I've done an R&R with a tandem antenna install yet.

[Surcouf]

My water tight cylinder is a work in progress, but to help anyone else with this question, I have attached some photographs.

I installed the FrSky TD R10 receiver in the battery compartment with the 2.4 GHz short extension installed. I then attached the long extension and routed it through the center conduit as Bob mentioned. I wasn't sure if the brass coupler would also fit with the servo extensions and power wires, but it slid in without too much issue- see the attached picture for where it appears in the conduit (battery compartment to the left).



I temporarily taped the receiver, the second original 2.4 GHz antenna, and the 900 MHz antenna where I believe it will work the best- see the attached picture. I may need to move them slightly once I hook up the servo cables to the receiver. If someone has a better suggestion, please let me know. I will also need to make sure the AD2 and mission switch will fit- I do not believe that will be a problem.



I then have a picture of how I routed the antenna extension out the rear endcap. I removed the R&R On/Off switch and pushrod, and routed the antenna through the bulkhead gland. The o-rings are a tight fit, but I may still need to seal the outside of the brass ferrule (not sure yet). As a side note- in this picture I am using waxed lacing cord around the antenna and vent tubing like we traditionally used on aircraft wire harnesses before zip ties. I feel they work better, and do not have sharp edges to cut you or other objects. The original vent tube zip ties are there, but for wiring or antennas it is another method to consider for someone looking for a clean installation. As Bob mentioned, the antenna does reach the sail, and will have just enough length to be fed up a periscope mast on the Victoria model I am installing this in.



I hope that others will find this helpful. I hope that answers your question Tim.

[type7]

Why do you want the antenna sticking up externally? That receiver automatically switches to 900mhz when you submerge and uses 2.4 ghz on the surface with the antenna in the cylinder.

[Timothy L]

Surcough -
Thank you so much for your description - well stated and very helpful. The “waxed lacing cord” - is that a product designed for this purpose? Where do you normally source it? Thank you again.
Tim

[Surcouf]

Why do you want the antenna sticking up externally? That receiver automatically switches to 900mhz when you submerge and uses 2.4 ghz on the surface with the antenna in the cylinder.

I look at it as options. Distance to the boat, contaminants in the water degrading the signal, etc. This way I maximize the ability to maintain control.

[TuptubBuilder]

May I suggest a much simpler solution. First of all, I am not an Electrical Engineer and don't want to get into standing waves or impedance matching but due to telemetry, the Rx transmits as well as receives. In simple terms, don't mess with the antenna. Extending the antenna for reception only is ok. You just loose some signal gain. Get a Frsky R9, assuming you only need 6 channels. It's 900 MHz only and the dipoles have higher gain than the single TD10 does.

[Surcouf]

Surcough -
Thank you so much for your description - well stated and very helpful. The “waxed lacing cord” - is that a product designed for this purpose? Where do you normally source it? Thank you again.
Tim

Tim,

It is a flat waxed cord that meets Mil Spec- MIL-T-43435 for aircraft use. Now for this purpose it does not need to meet a spec, but most cord for sale is not flat, even when they say it is. The flat cord holds knots really well.



A roll will last several lifetimes for most people, and can be found at places like Aircraft Spruce, but feel free to look for a cheaper source.

https://www.aircraftspruce.com/catalog/elpages/BreydenLacingTapes.php

Part# 11-02013

Tie it how you would like, but the original concept is a clove hitch, followed by a square knot. The FAA document AC43.13-1B describes it in section 11:




Not only is this a nice alternative to zip ties with sharp edges if not cut flush, if you have a lot of wire runs in a small compartment, the cord ties do not take up as much space if volumetric space is at a premium.


Tony

[Surcouf]

May I suggest a much simpler solution. First of all, I am not an Electrical Engineer and don't want to get into standing waves or impedance matching but due to telemetry, the Rx transmits as well as receives. In simple terms, don't mess with the antenna. Extending the antenna for reception only is ok. You just loose some signal gain. Get a Frsky R9, assuming you only need 6 channels. It's 900 MHz only and the dipoles have higher gain than the single TD10 does.

I appreciate the feedback. For better or worse, I have gone down this rabbit hole for this project. My neighbor's pool will be my first location for testing before going to open water, and it is a saltwater pool- not sure how much it would affect it. I will find out when I submerge the model and see at what depth the loss of signal occurs.

If I end up making one of the shark models, then the R9 looks like it would be a good choice, if it handles that level of salinity for a reasonable depth. I know Bob and Ed did some videos on the 900 MHz in a chlorine pool, and it did well. It would be interesting to know if others have tried the 900 MHz in a saltwater pool, and what their results were. I know the salinity is not that much in a pool, but is there an effect that is appreciable? If it works well it would simplify a build for sure.

[Timothy L]

Thanks Tony

[TuptubBuilder]

I appreciate the feedback. For better or worse, I have gone down this rabbit hole for this project. My neighbor's pool will be my first location for testing before going to open water, and it is a saltwater pool- not sure how much it would affect it. I will find out when I submerge the model and see at what depth the loss of signal occurs.

If I end up making one of the shark models, then the R9 looks like it would be a good choice, if it handles that level of salinity for a reasonable depth. I know Bob and Ed did some videos on the 900 MHz in a chlorine pool, and it did well. It would be interesting to know if others have tried the 900 MHz in a saltwater pool, and what their results were. I know the salinity is not that much in a pool, but is there an effect that is appreciable? If it works well it would simplify a build for sure.

Got it. You have an interesting situation. It sounds like you will be restricted to periscope depth in a salt water swimming pool. In this case, tuning the 2.4GHz extended antenna for optimum range really isn’t an issue. Best of luck to you.