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Old 08-10-2018, 08:03   #1
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Compromise question for the HF fanatics

Hi all,

I have to compromise. Yep, that dreaded word.

The layout of the boat/rig/ground plate have presented me with the following choices.

I can place the antenna tuner (AT130) in the aft cabin, near the rear stay HF antenna. That's how it is setup currently, with about 5 meters of wire from the tuner to the lower insulator on the backstay.

HOWEVER, this means the tuner is nearly four meters from the ground plane device. (one of those Italian porous style things), currently connected via a piece of flattened copper pipe.

So, in my situation, would you move the tuner closer to the ground plane, and run a longer lead to the rear stay, or would you leave it as it is?

I think I can get the run from the tuner to the ground plane down to about 1.5 meters, but doing so will add 2.5 meters of tuner lead.

I ask because I am about to order some copper tape to replace the pipe, which is a PITA to route through the cabin, and they don't give that copper tape stuff away.

Matt
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Old 08-10-2018, 10:38   #2
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Re: Compromise question for the HF fanatics

Your antenna actually starts at the tuner, which is why you want the cable run between your tuner (which is part of your antenna) and what you commonly call the antenna to be as short and in line with the antenna, as possible. Curves and angles degrade your signal. On the other hand, the connector to your ground plane, usually copper strapping, but copper tubing, in your case, is not very much affected by length or by angles and curves, as long as they are done correctly.



Thus, the position of the tuner, relative to the rest of the antenna system, is vastly more important. Hope this is clear enough.
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Old 08-10-2018, 12:02   #3
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Re: Compromise question for the HF fanatics

Matt,


I would stick with your current situation - and you are doing the right thing in replacing the flattened pipe with proper copper strap.

You are probably going to want to invest in a sack of clip-on ferrite filters to keep RF out of any other wiring - and what is affected will depend on the frequency in use. Stuff like USB cabling, stereo speakers and the like are the most common, but you never know (autopilots are famously affected by HF radio transmissions!). The long ground lead will make this worse, as it will allow a larger RF field inside the boat.


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Old 08-10-2018, 14:52   #4
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Re: Compromise question for the HF fanatics

Thanks guys.

Looks like the tuner is staying where it is then, I can’t get it any closer to the backstay than where it is now.
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Old 08-10-2018, 15:05   #5
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Re: Compromise question for the HF fanatics

I don't think it will make much difference.


I believe there would be a slight advantage to moving it lower. As pointed out upthread, the antenna starts at the back of the tuner. Moving the tuner lower makes the antenna longer. A longer antenna is more effective, particularly on lower bands. On the other hand, having a longer ground wire doesn't accomplish anything useful.


But the difference is slight.
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Old 10-10-2018, 13:44   #6
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Re: Compromise question for the HF fanatics

Matt,
Even though you asked about "compromise", I will answer you...

In this situation (on-board a sailboat, with a "compromise" antenna system during the best of times), the short answer is:
Leave the tuner where it is now....just run a wide copper strap from the tuner ground lug to the underwater plate!!

Yep, that is opposite of what we'd recommend if you had a vertical on-shore, with a counterpoise / radial system (where you want the feed point as physically close to the ground system / radials, as possible)


In addition to remembering that the antenna starts AT the remote tuner, the antenna ground system starts at the tuner as well...but, you can make 'em do their jobs differently...

For the "antenna" you desire to keep it (the GTO-15 and backstay) as far away as possible from other devices/systems on-board (to reduce both transmit and received RFI), and to keep as much of the antenna in the clear / unobstructed as possible (to improve its transmit effectiveness / efficiency)...also remember that for the freqs/bands that the antenna (GTO-15 and backstay) is shorter than 1/4-wavelength the antenna feed point is the high current point (and even on the bands where it is a bit longer this high current point is usually quite low)....and it is the high current point / high current area of the antenna that does most of the radiating / provides most of the signal (both transmit and receive)...
SO...
So, getting that point up and out of the boat, away from anything else metallic and away from other systems/devices and in the clear / unobstructed, is important to antenna efficiency / effectiveness on both transmit and receive!!!

For the "antenna ground" you want as much RF conducting material (copper strap, sea water, etc.) as close to the tuner ground lug as possible...
But, you can quite easily adapt/compensate here...
You can easily add some more copper strapping, from the tuner ground lug to the underwater plate...

In your case you have a "flattened copper pipe" (actually not a bad idea, but usually a waste of time/effort, as a wide copper strap is not expensive at all), and if you simply replace it with a 3" to 4" wide copper strap (a copper "strap", not "foil"), and run the 4 meters (~ 12' - 14') between the tuner and the ground plate...
And, you'll have as good (or better) antenna ground / RF ground than most!!

Please note that I'm using the word "strap" and not "foil" or "tape"....
"foil" or "tape" is thin, typically .001" to .003" thick and can be easily cut with scissors....it can also be torn / ripped by hand....and if used in a sea water / salt air marine environment without painting/coating/epoxying, it can quickly become eroded and torn....
"strap" or "strapping" is typically 012" to 040" thick, and cannot be cut with scissors, nor can you tear it by hand....while I always paint/coat it (so it lasts decades), even if left bare in the bilge it will last years...

I know you are down-under, and I don't know suppliers down there, but here in US copper strapping is fairly inexpensive....compared to what the radios cost!!
https://www.gacopper.com/index.html
https://www.gacopper.com/012-CopperStrap.html
https://www.gacopper.com/022-CopperStrap.html
25' (~ 8 meters) of 3" wide (0.012" thick) copper strapping is $59 USD
and 25' of 3" wide 0.022" thick strapping, is $93 USD...

Do not use thin foil or "tape"....it is too easy to destroy/tear...and unless coated well, it will corrode in a few years...
Please do read this other posting...it will help..

HF/SSB


Now, since I haven't seen your boat, nor your install, I cannot give you an absolute 100% set-in-stone guaranteed to be perfect answer...
And, your mention of "5 meters of wire from the tuner to the lower insulator" makes me want to be clear....if this is out in the clear, that's perfectly fine....if that is snaking thru some lockers / thru the bilges, etc., then this is not good...

So, to be clear....if you can get the tuner as close to your backstay as possible, and keep the GTO-15 wire running straight, and away from being parallel to other wires / metallic objects (like a stern rail, etc.), the better you are!!
Do not worry about the GTO-15 wire running along the backstay!! This is not a problem at all, and needs no stand-offs....except/unless you have a steel or aluminum boat, and/or have a something else on the backstay that you need to route the GTO-15 around (like a radar mount, or hydraulic backstay adjuster, etc.)....
Just keep it running as straight as you can from the tuner to the backstay, and keep it from running parallel to other wires / metallic objects, as best you can, and you're good!!



If you really want to worry about it, and take a fanatical approach (like I do), then you can do what I do/did and run a really wide (6" wide) thick copper strap....mine is about 7' to 8' long, from the tuner to two underwater Dynaplates...
(and I also have a short, 1.5' long, 3" wide copper strap from the tuner to two flat metal tanks....and another 3" wide copper strap running about 12' from the Dynaplates, forward to a keel bolt....now, it's doubtful this connection to the keel does anything for me, but it doesn't hurt, and I am a radio nut... )


Please have a look at this posting of mine from earlier today....it deals with antenna ground / RF ground...
HF/SSB

Also, have a look at these pics...


This shows the end of the 6" wide (0.032" thick) copper strap attached to two Dynaplates....and the end of the 3" wide (0.022" thick) copper strap that runs forward to a keel bolt...



This shows the two 18" x 6" Dynaplates....(I have Marelon thru-hulls)
Note that I could've installed a bit further up, closer to the tuner....but knew I wanted to keep 'em submerged all the time, even in heavy sea offshore and that I was going to use 6" wide strap (instead of the standard / typical 3" wide strap), so I decided to place 'em here!!



Hope this helps...

fair winds

John
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Old 10-10-2018, 17:53   #7
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Re: Compromise question for the HF fanatics

Quote:
Originally Posted by ka4wja View Post
Matt,
Even though you asked about "compromise", I will answer you...
Geez John, I put "HF fanatics" in the subject line so you'd find it, I hadn't considered that the compromise part would put you off.

Thank you for your great and detailed response, you've put my mind at ease.

On the whole copper pipe thing, I did that because it was WAAAAYYYY cheaper than copper strap here in Australia.

The cheapest price I have been able to find here in Australia is AU$25 per METER for strap! So, around US$20 per meter, or to put it in perspective, the 8 meter US$59 roll you suggested would cost me US$160 if I were to buy it here in Oz.

By contrast, the length of copper pipe I used cost me only AU$23. But it is a nightmare to feed through the interior so currently just crosses the lazarette cabin in free space.

I had seen those guys you linked to in your post, I shall email them today and see if they will ship to Oz and how much that would add to the price.

Now that you've reassured me, as have others, that the tuner can be a reasonable distance from the ground plate without problems (thank you for explaining that it matters on land based rigs not marine, it explains where I was getting the dire warnings about keeping the distance short on the earth strap.), I will mount the tuner in the optimal position near the backstay and see how much strap I need.

I was interested that you didn't feel the need for standoffs from the lower part of the rear stay rigging. That is at odds with just about every installation I have seen. Can you elaborate?

Matt
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Old 10-10-2018, 19:53   #8
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Re: Compromise question for the HF fanatics

Matt, FWIW try pricing the Cu strap ex the UK, I have found postal costs from the UK to be waaaay cheaper than similar items from the USA.

Also, if you get stuck, I have a maybe 2 metres of 50mm Cu strap you can have for free
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Old 10-10-2018, 22:55   #9
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Re: Compromise question for the HF fanatics

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Old 11-10-2018, 11:09   #10
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Re: Compromise question for the HF fanatics

Always better to have tuner close as possible to backstay for two very important reasons:
- the actual RF current, Henderson RF ‘radiation’ of your signal (and receiving efficiency) is a function of wire distance from the tuner. By having a horizontal run of 5-10’ before getting it vertical is wasting a significant amount of you xmit/ receive signal. Vertical antennas talk to/ receive better with other vertical antennas... horizontal antennas work better with other horizontal antennas... its call proper polarization is tech speak. Antenna current distribution is not linear. That is... if you have the first 10% of the wire from the tuner at horizontal AND low height... the transmitted signal is much more than 10% reduced

2) Of course defends on what RF noise producing equipment you have on your boat (LED lights, iPhone chargers, laptops, TVs, computers, fans, Chartplotters & auto-pilot circuits/ their internal noisy computer chips,... but their RF noise is on/ carried easily around the boat on the boat’s General wiring. The least proximity to other boat wiring the better (certainly DO NOT bundle the output tuner wire going to the backstay with any bundle of 12v or 120v wires!!). The coupling of this noise RF to the antenna wire increases dramatically with proximity. Marine HF signals are already on the weak side given distant between stations, 100w powers, marginal antennas... so it’s very important to install your antenna system is stay away from/ reduce your local noise as much as possible or you won’t be able to hear those that can hear you.

It’s does’t take too much very much disregard of good ‘tuner to antenna’ installation practice to reduce your transmitter and receive range to half or more. Just because you can hear some signal very strongly, doesn’t mean you have an efficient receive/ xmit station. Radio energy works on a logarithmic scale which means signal strengths fall off fast... and 80-90% of your range depends on your ability to hear weak signals.
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