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-   -   Standoffs - Antenna to Backstay Insulator (https://www.cruisersforum.com/forums/f13/standoffs-antenna-to-backstay-insulator-27407.html)

Ramblin' 16-06-2009 08:36

Standoffs - Antenna to Backstay Insulator
 
I asked this on another thread, but got no responses. (The GTO Wire)

We are redoing our tuner/backstay connection and looking for advice and/or ideas for stand-offs. We previously used pieces of hose, lengths of hose and I've been told you can put a shroud "cable" over the wire. I googled stand-offs and nothing that seemed applicable popped up. Any ideas appreciated. Sounds like a lot of you people are familiar with radio installations.

Thanks

senormechanico 16-06-2009 09:16

I'll probably start a flame war or something but here goes...

On our previous boat I only had one backstay insulator near the top.

After disconnecting the bonding wire from the chainplate, I fed it directly from the antenna tuner.

Nobody believed I wouldn't get shocked when transmitting, but although there's maximum current at the fed end, there's also minimum voltage there as well.

I proved my reasoning to several people by having a HAM friend talk on 20 meters while I stood at the stern while holding the backstay.

I demonstrated it by holding it from different heights from the deck to as high as I could reach without so much as a tickle.

The radio was an ICOM 735 barefoot, but running at full chat.

Over the years, I got lots of positive comments about my signal quality.

Think of an end fed antenna as working similarly to a bull whip. A lot of muscle is put into the handle end, but not a lot of speed.

The other end has enough speed to break the sound barrier, but not much "muscle".

I wouldn't even think of touching the upper end while transmitting!

Steve B.

Cheechako 16-06-2009 09:22

a piece of small hard plastic tubing with a notch in each end works well. Take a long tie wrap, wrap it around the back stay, pass it through the tubing and cinch it around the cable.... basically a loop with the cable at one end and the backstay at the other and the plastic tubing held in between...

GordMay 16-06-2009 09:33

2 Attachment(s)
Rather than hose, I've always used rigid Nylon or PVC tubing, secured to backstay & GTO with a tie-wrap.
I cut the tubing with a drill (or rotary rasp), forming concave ends to cradle the wires.
Run the tie-wrap though the tube, around the stay, back through the tube, and secure around the GTO.

Cheechako 16-06-2009 09:53

Dont forget the dielectric grease on the backstay attachment area!

fairbank56 16-06-2009 09:54

Depending on frequency, antenna length and your ground plane system, the voltage at the the lower end feed point can be quite high. That's why there is a high voltage insulator on the tuner and why we use high voltage cable to connect to the backstay.

Eric

senormechanico 16-06-2009 11:07

I had a 3' straight copper foil to an external copper plate (not a dynaplate) and the output of the tuner was only 16" from the chainplate. I tried every frequency band I could legally transmit on (Advanced ticket) and never got even a tiny tingle. The radio covered 0.5/30 Mhz. but not include the 2 meter band. If it had, I'd not want to mess with the backstay under at those frequencies.

Steve B.

Ramblin' 16-06-2009 13:42

Senormechanico, Cheechako, Gordmay and fairbank56, thank you all for your responses. All very interesting comments to digest. I've printed out the information and will give to the engineer on our vessel.

GordMay, thank you for the images, it looks like a very tidy installation. One question, on the image with the "little windows" describing the image, it shows the antenna cable connected to the backstay above the swage. In one of the many searches I have done, it was recommended you attach the cable to the smooth part of the swage rather than the wire backstay for a better connection. We were advised to strip the cable and attach directly to the swage and then wrap with waterproof tape (I'm assuming you put the dielectric grease on before the tape).

Sorry for all the questions, but on our last 6 years of cruising Mexico, our success with the radio was "hit & miss":o. We are trying to do a little better this time:smiling:

Thanks again to all for your comments, it really helps.

senormechanico 16-06-2009 13:52

Another advantage of attaching the tuner to the chainplate (at least in my installation) was that it could be done with a standard ring connector under a chainplate ss nut fastener belowdecks. This had no environmental problems (salt, corrosion etc.) during the entire time I owned the boat.

Steve B.

Rick 16-06-2009 17:07

Seniormechanico
 
My experience has equaled that well stated by Seniormechanico. There is every disadvantage in paralleling the GTO feed line with a grounded backstay lower "stub" the radiation pattern will be poor when compared with driving the backstay from inside a lazarrette directly.

GordMay 16-06-2009 17:19

Quote:

Originally Posted by Ramblin' (Post 293861)
... on the image with the "little windows" describing the image, it shows the antenna cable connected to the backstay above the swage. In one of the many searches I have done, it was recommended you attach the cable to the smooth part of the swage rather than the wire backstay for a better connection...

I cannot claim to be an authority on antena installations; but your comments sound right to me. On general principles, I'd expect the smooth, solid swage to make a better connection.
I'd defer to BTrayfors, Rick, Seniormechanico, or any of our other real experts, on this one.

btrayfors 16-06-2009 17:57

Well, here's where we get squarely into the realm of emoting rather than pontificating based on solid RF radiation principles.

I, too, am an affectionado of the "feed the chainplate" view. In fact, I just counseled a client with a 44' catamaran to install a single insulator high up on the topmast shroud, and we'll feed the thing from the chainplate belowdecks. Neat, efficient, protected from weather, easy to implement, etc., etc.

However, this won't work in every case. Most insulated backstay antennas -- or "alternate backstay antennas", like mine --- are fed via a GTO-15 wire run from the tuner belowdecks thru a waterproof deck fitting and up to the backstay. If you take this route, you'll be well advised to use some sort of standoff insulators for the GTO-15 wire. I've found that the best way to do this -- for me and my clients -- is to use 5/8" solid nylon rod. Cut into 2" lengths, drill a hole lengthwise thru the bar, and use plastic wire ties to hold the insulator in place. No need to cut grooves. Works fine, looks neat, and is inexpensive. The 5/8" solid nylon bar is available from US Plastics, among other sources.

I am also a believer in not worrying too much about the potential for RF burns. As an old ham who's built many rigs and experimented for many years, I KNOW what RF burns can be like. Stick your fingers in the final coil of a transmitter....yeah, that can be dangerous. Burns from the bone outwards.

BUT....at the power levels used on a boat, and with the typical backstay installation, it's unlikely anyone's gonna get an rf burn. Even if they happen to be hanging onto the backstay while someone is below transmitting, at most they'd feel a tingle and would damn well remove their hand quickly before any damage was done. Ditto for the RF ground systems, e.g., toerails or lifelines. IMHO, this just isn't a problem. Sorta like worrying about the varnish job when the ship is sinking :-)

Bill

Aparrotwind 18-06-2009 19:49

I just installed our new ham with backstay for antenna, but while in the harbor I cant seem to pick up much. I have an automatic tuner and copper foil under the waterline - grounded to the motor mount. Will I get better reception out on the open water? Or do I have other problems that need be addressed?

btrayfors 19-06-2009 03:37

Reception in marinas is generally bad. Too much interference from other boats, marina equipment, etc.

Re: your copper foil, usually it's a better bet to run it to the nearest bronze thru-hull, not otherwise connected to the boat's grounding systems. You get better grounding this way, and less potential for radio frequency interference (RFI).

Also, what you hear is very much dependent on propagation, frequency, and time of day. Try getting WWV or WWVH on 5mHz, 10mHz, 15mHz. Also, try tuning the different ham bands....mostly 40 and 20 meters during daytime, and 75 meters at nite.

Also, try reducing onboard interference by turning off all AC and DC equipment on board while listening, then slowly turn each on and see if you hear any interference. Motors, computers, and digital devices are notorious. Inverters, frigs, etc. can play havoc with HF reception. On my boat, I found that a digital voltmeter was causing a lot of interference.

Good luck,

Bill

Aparrotwind 19-06-2009 18:58

Thanks Bill, I'll try rerouting to a thru hull fitting this weekend and see if my reception gets any better. The boat beside mine gets a lot better reception so I know I have some issue(s) going on. I appreciate the feedback.


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