75 mhz antennas

[rwtdiver]

Issues with the 75 mhz antennas that we use for our submarines. Running subs in chlorinated pools and salt water.

I know I have run into some issues running my subs even on the surface with the VEX 75 mhz receivers in my pool. The antennas are normally below the water line (inside the WTC) even when it's on the surface. I have found that if the pool is heavily chlorinated, I have issues with reception as far as distance. The less chlorination the better the reception.

My question is if you installed the antenna up into the sail like you do with the 2.4 receiver antenna would that solve the problem? Or would you still have to shield that portion of the antenna that is still below the water line?

I would assume this would be the same situation with reception if you were running your boat in salt water!?

Rob
"Firemen can stand the heat"

[SubDude]

I route the antenna through a piece of brass tubing through a bulkhead and into a length of 1/8" ID Neoprene tubing that has a piece of brass rod in the end. That way it is at least outside the WTC and all sealed up. I just lay it inside the hull.

[He Who Shall Not Be Named]

Issues with the 75 mhz antennas that we use for our submarines. Running subs in chlorinated pools and salt water.

I know I have run into some issues running my subs even on the surface with the VEX 75 mhz receivers in my pool. The antennas are normally below the water line (inside the WTC) even when it's on the surface. I have found that if the pool is heavily chlorinated, I have issues with reception as far as distance. The less chlorination the better the reception.

My question is if you installed the antenna up into the sail like you do with the 2.4 receiver antenna would that solve the problem? Or would you still have to shield that portion of the antenna that is still below the water line?

I would assume this would be the same situation with reception if you were running your boat in salt water!?

Rob
"Firemen can stand the heat"

The West coast guys have been running a portion of their 75mHz antenna up a mast in salt water for decades. As the lower frequency antennas are fractional, they don't need to capture the entire wave of the RF carrier, so even a small portion of the antenna projecting into the air will capture the signal. So, yeah. Run the antenna up into the sail, and no need for a shielded coaxial cable between receiver and antenna proper.

David

[rwtdiver]

The West coast guys have been running a portion of their 75mHz antenna up a mast in salt water for decades. As the lower frequency antennas are fractional, they don't need to capture the entire wave of the RF carrier, so even a small portion of the antenna projecting into the air will capture the signal. So, yeah. Run the antenna up into the sail, and no need for a shielded coaxial cable between receiver and antenna proper.

David

Thanks for the information David.

I am going to try mounting the antenna high in the sail with one of my boats and check the results. My 1:77 scale Nautilus works great in the pool, but the antenna is mounted inside the Sub Driver and more to the top side of the cylinder when it is on the surface, as soon as submerge to just the top of the deck I started to get glitches in the signal. The pool that day was pretty much sedated with chlorine

Interesting how transmitter signals react to chlorine and salt in water!

Rob
"Firemen can stand the heat"

[Bob Gato]

Whenever I knew that my sub buddies were coming over to run models in my swimming pool, I would run the chlorine down to almost nothing and when they were gone it was time to shock the pool and bring it all back up to normal...

[rwtdiver]

Whenever I knew that my sub buddies were coming over to run models in my swimming pool, I would run the chlorine down to almost nothing and when they were gone it was time to shock the pool and bring it all back up to normal...

I do the same Bob. I just plan a little ahead and if I know I am going to run my subs, I let the chlorine bleed off a little a couple of days ahead of time.

Rob
"Firemen can stand the heat"

[rwtdiver]

I have a question about the 75 mhz antenna wire itself. If you are running your antenna outside the wtc does it have to be incased in some sort of tubing or is it ok just the wire itself?

Rob
"Firemen can stand the heat"

[trout]

Rob,
I run my antenna free in the hull. I seal the very end with silicon and shrink tubing. That being said, I am a gorilla with my subs sometimes. I had a. sub that one week was super great and the next it inhaled on receiving signal. I checked the antenna and there was a slice in it. I must have pinched it between the hull halves. So, sealed that with silicon and life was good again.
Peace,
Tom

[rwtdiver]

Rob,
I run my antenna free in the hull. I seal the very end with silicon and shrink tubing. That being said, I am a gorilla with my subs sometimes. I had a. sub that one week was super great and the next it inhaled on receiving signal. I checked the antenna and there was a slice in it. I must have pinched it between the hull halves. So, sealed that with silicon and life was good again.
Peace,
Tom

Thank you Tom,

I am very happy that I do not have to try and thread the antenna through a silicone tube. I did that on my Russian Alfa boat, and what a pain in the you know what that was! OK I will make sure to seal the tip up with some silicone and heat shrink!

Thanks again Tom!

Rob
"Firemen can stand the heat"

[Bob Gato]

"If you want something done the easiest way give the job to the laziest person"... Take a length of thread and attach it to a q-tip cut short.. you might have to cut the diameter of the fuzzy head down by pulling off some of the cotton.. then blow the q-tip with the thread trailing behind through the tube with some compressed air.. then pull the antenna wire through with the thread. I once ran strobe light wires 20 feet thru a 5/16 conduit through the wings of a King Air 200.. it took 5 minutes to do both sides.-BG

[rwtdiver]

"If you want something done the easiest way give the job to the laziest person"... Take a length of thread and attach it to a q-tip cut short.. you might have to cut the diameter of the fuzzy head down by pulling off some of the cotton.. then blow the q-tip with the thread trailing behind through the tube with some compressed air.. then pull the antenna wire through with the thread. I once ran strobe light wires 20 feet thru a 5/16 conduit through the wings of a King Air 200.. it took 5 minutes to do both sides.-BG

Thank you Bob,

But I think I will pass on that one! I am sure if you have done this then it must work..

Rob
"Firemen can stand the heat"

[trout]

I got one better and it is what I am moving to more and more. Just keep the antenna in your dry space. I have done elegant zig-zag and just waded the antenna in there (and I read all the experts that talk about crossing your antenna) they all worked. If you are going to use your antenna in the wet, put a rod in your bulkhead and solder your antenna to each end. The rod should extend interior and exterior to the bulkhead. That way once you seal that rod in, water will not creep back into your dry space. David used a threaded rod and used nut and washer to fasten the antenna down.
Here is my current Skipjack no exterior run great signal.

[Bob Gato]

Just visualize the wave coming off your transmitter antenna like in a NCIS show animation and visualize that wave cutting across the antenna of your model... The more of the full wave that cuts across that receiver antenna, the stronger the received signal. If the antenna is curled up inside the WTC I would think the reception is not as strong as if the antenna was presenting itself in its full length or as full length as possible to those waves.

[trout]

Bob, no argument from me. I am not smart enough to understand all the science in radio propagation or reception. Maybe the crumpled antenna or the one in the Skipjack above have reduced range, I just never saw the difference in the waters I ran or the distances I went. This is my experience, your mileage may vary.

[Bob Gato]

You know Tom you probably right... The old megahertz radios had so much non line of sight power.. with a correctly set up non glitchy sub, you'd probably never see the difference.. except maybe past 6 feet down.