One for the hams - antenna wiring

Conachair

Conachair

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I want to install an insulated backstay on a steel boat but a few bits I'm not too sure about. Schematic below. Tuner will be in the lazerette, as close to the stay as poss but still dry. So...

  • To use the hull as a ground plane I connect the core of the PL214 to the stay and the sleeve to the hull - correct??

  • What sort of wire should I be using for the ground connections, and from the tuner to the stay - thinking of something fairly heavy duty.

  • Will the 2m or so run from the tuner PL214 output shield to the engine block make much difference? Don't want to connect to the hull next to the tuner. More than one ground connection to the hull would keep me awake at night worrying about corrosion.


All thoughts welcome :)

radio%2520wiring.JPG
 
The antenna output from the tuner goes to the backstay through high voltage wire, not coax. It could be the inner of a large diameter coax, with the screen removed. This should be spaced away from the hull and any ungrounded part of the backstay, a few inces are normal.
The antenna starts at the tiuner, even if some of it is inside your metal box!

DO NOT use coax with a screen from the tuner antenna connection. It adds capacitance from the bottom of the antenna to ground and is bad news for the capability of the tuner to tune the backstay to a wide range of frequencies.It does nothing good.

The ground of the tuner goes to the metal hull or to the engine block assuming that it is connected to the hull.

As you now have only one ground connection make it as close to the tuner as possible.
2m would be OK but use copper tape, preferably at least 2 inches wide. MUCH better than even heavy duty wire.
 
Tuner connection

Just to reiterate. I think the tuner should be earthed at the hull near the tuner. If it worries you make this the earth for the radio as well. Any long earth wire will be part of the antenna so will radiate inside. Likewise as said the connection to the antenna should be as short as possible. Make the through deck connection via an insulated feed through. This is a high voltage pointy so susceptible to water causing leakage.
good luck olewill
 
I agree with everything said above.

BUT have to reiterate the point, you have a steel boat, the perfect groundplane. Connect the tuner ground to the hull right at the tuner. Why mess with wide copper tape when you have the ultimate connection right there. Forget the engine block it will be nowhere near as good as the hull. It is a critical counterpoise not an 'earth' in the normal electrical sense. An entire steel hull immersed in seawater should give you a spectacularly good system.
 
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Well sounds like I want to get the ground to the hull close to the tuner.

The problem with connecting to the hull next to the tuner is that you have 2 connections between the hull and the batt neg, which is a bad thing. The engine block is the only place where batt neg is attached to the hull. There would be continuity between the hull at the tuner, go back through the coax from the tuner to the radio and the batt neg. I just metered it out to check The ground would need to be connected through capacitors to stop any DC getting through.

Found this..

http://www.sailmail.com/grounds.htm

Fasten the tape securely to an insulating piece of phenolic or to a terminal strip, cut a 1/10-inch gap across the tape, and solder several 0.15uF ceramic capacitors across the gap. These capacitors will be transparent to the RF, which will be happily grounded by the ground tape system, but they will block any DC currents from running through the RF ground system
Click to expand...

And this... http://www.electronicspoint.com/dc-blocking-capacitors-voltage-rating-t114168.html


About the ground - is that the shield of the pl214 output on the tuner or the ground lug? Or should the ground lug get connected to the radio ground lug?

Thanx all.
 
With a metal hull, I would split the ground connection and insert a handful of 0.1-0.5 uF capacitors: you cut the RF ground strap and solder one leg of the capacitors on one side, the other leg on the other end of the cut.

ATU ground stud ---> 1st copper strap piece --> capacitors ---> second copper strap piece --> hull

They would let HF pass freely, but they would stop any unwanted DC from flowing.







edit: too late :D
 
The use of copper tape for the ground connections is essential,

I would use tape from the radio, to the tuner, from the tuner to the nearest point on the hull. At each connection, fold the ends over & drill through for the size of the ground terminal.

The idea of using tape rather than wire is to reduce 'skin-effect', simply put, at RF frequencies the current will migrate to the surface of the conductor, the higher the frequency, the more effect, so maximizing the surface area of the conductor is a good thing.


If the tuner has a PL-214 socket for the antenna (unusual) do not make any connection to the outer, insulate well, there is potential for several kV of RF there.

I would also sleeve any part of the back stay reachable by hand, RF hurts !


73's

I would not worry too much about possible corrosion problems, if it done right, the copper tape will be a lower resistance path than the hull.
 
starfire said:
The use of copper tape for the ground connections is essential,

I would use tape from the radio, to the tuner, from the tuner to the nearest point on the hull. At each connection, fold the ends over & drill through for the size of the ground terminal.

The idea of using tape rather than wire is to reduce 'skin-effect', simply put, at RF frequencies the current will migrate to the surface of the conductor, the higher the frequency, the more effect, so maximizing the surface area of the conductor is a good thing.
Click to expand...

Any idea where I might get some insulated ground strap long enough?


If the tuner has a PL-214 socket for the antenna (unusual) do not make any connection to the outer, insulate well, there is potential for several kV of RF there.
Click to expand...
Meant PL 259/ SO 259 on the tuner. So the "other half" of the signal would go out the ground lug on the tuner?



I would not worry too much about possible corrosion problems, if it done right, the copper tape will be a lower resistance path than the hull.
Click to expand...
I would worry lots :eek: It is fairly well documented and possible not something to get tto bogged down with here. But more than one connection between batt neg and the hull is a bad thing.

Again THANX ALL :)
 
Conachair said:
Any idea where I might get some insulated ground strap long enough?

http://www.sailcom.co.uk/antennas/index.html#Dynaplates on that page, they also do a DC isolator for about £24 & Suitable HV cable for the connection to the backstay.

Meant PL 259/ SO 259 on the tuner. So the "other half" of the signal would go out the ground lug on the tuner?

Yes




I would worry lots :eek: It is fairly well documented and possible not something to get tto bogged down with here. But more than one connection between batt neg and the hull is a bad thing.

Ok

Again THANX ALL :)
Click to expand...

.
 
Conachair said:
http://www.sailcom.co.uk/antennas/index.html#accessories

Handy site, thanks. Slowly getting there. :)

Icom manual says for the ground-

Would some welding cable or similar be that different to strap for the radio ground?
Click to expand...

Just got back to this, I'm a bit confused.


You are planning to connect to the hull at the tuner aren't you?! For the paranoid, those capacitors you referred to up there will completely block any dc and take away any concerns about extra connections to the hull.


For a few inces from lug to hull pretty much anything will do. If you look inside your tuner you will almost certainly find they have used tinned copper braid to make the connection to the lug.
 
whipper_snapper said:
Just got back to this, I'm a bit confused.


You are planning to connect to the hull at the tuner aren't you?! For the paranoid, those capacitors you referred to up there will completely block any dc and take away any concerns about extra connections to the hull.


For a few inces from lug to hull pretty much anything will do. If you look inside your tuner you will almost certainly find they have used tinned copper braid to make the connection to the lug.
Click to expand...

There seems to be consensus on the connection between the tuner and hull, but I'm still not sorted as to what to do and how with the earth lug on the radio. If the shield of the SO259 is unconnected and the "other side" of the signal goes to the hull through the earth tab on the tuner, then I'm a bit wary of connecting the radio ground tab to this, with all that power coming out of it.

Take 2? ....

radio%2520wiring%25202.JPG
 
The radio should be connected to the ATU with good quality coax with both inner and braid soldered at both ends. I think there was som confusion over the output of the Atu being a SO239. The output of my Atu is a ceramic insulator with a wing nut on the stud through it. I have some high voltage line that connects that to the backstay.

I chatted to someone in USA last year when the boat was still in it it's cradle in the yard with effectively a tiny bit of wire as a counter poise instead of a proper earth connection to the surrounding sea.
 
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