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Author Topic: Sirio Gain Master 10meter vertical  (Read 2237 times)
KEVIN1218
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Posts: 19




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« on: February 04, 2013, 06:19:42 AM »

http://www.gain-master.it/

Hello.....I am expecting this Sirio Gain Master antenna today (see above link). The question I have is this;
I will ground the 10' galvenized antenna mast to (1) 8' ground rod using #12 insulated copper wire that is 5' long.
Do I need to ground the antenna as well, there are no radials for this vertical?

Thank you in advance for your input,
Kevin
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AA4PB
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Posts: 12769




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« Reply #1 on: February 04, 2013, 06:30:22 AM »

According to the spec sheet you provided, all metal parts of the antenna are DC grounded. That means that by grounding the metal mast you are grounding the antenna for lightning protection. You should also ground the coax shield on the outside of the house just before it enters the house (see the PolyPhaser web site for complete information).
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W5WSS
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Posts: 1683




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« Reply #2 on: February 04, 2013, 09:37:30 AM »

Hello, Kevin. The embedded antenna system part of the design is fine and may be dc grounded as you mention...but I do not like an fibreglass or any non conductive exoskeleton serving as a frame to hold the limp wire vertically.

We can very easily avoid this vulnerability with the use of fat Aluminium nested tubing that may then be wholly Dc grounded with a wander lead attached to a ground rod as you propose.

The problem with really getting a safe dc ground exists where we view this as a Dc circuit relative to static electricity and how much can build up on the fibreglass material expressed as a dielectric constant of the material where enough potential exists around the material we get catastrophic strokes to recover balance in the environment about the area.

These types of antennas are very active in this way and the problem with this approach in error dismissed as random lightning or bad luck.

The best approach is to keep the build up below discharge level in the first place and can be done using a conductive radiating element throughout the entirety of the vertical antenna.

We oftentime see the fibreglass antenna type pulverised by lightning for this reason I would avoid them especially in high lightning regions.
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W9GB
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Posts: 2611




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« Reply #3 on: February 04, 2013, 10:20:56 AM »

Quote from: W5WSS
I do not like an fibreglass or any non conductive exoskeleton serving as a frame to hold the limp wire vertically.
R -

This was changed (metallic vertical fixed antennas) in early Reagan Administration's Consumer Protection,
due to high rate of consumer electrocutions in 1970s installing metallic CB antennas and towers. 
SO, manufacturers largely switched to fiberglass vertical antennas and are required by federal law to have the Yellow/Red warning stickers and instructions to avoid power lines.

Family Radio Service (FRS), the planned replacement for CB service was introduced a few years later.
« Last Edit: February 04, 2013, 10:39:46 AM by W9GB » Logged
W5WSS
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Posts: 1683




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« Reply #4 on: February 04, 2013, 06:29:47 PM »

W9gb, Yes I was active that long ago and remember the adjustments to the manufacture.

Static buildup on the outside of the Fibreglass material is a real and serious concern because when it builds it can not be reduced by any other means except at it's own dielectric time constant and this occurs independently of the interior antenna.

The sticker warning consumers of the dangers of overhead powerlines is valid and is always included on any antenna today.

Aluminium vertical antennas are legal and being manufactured for amateur service.

73
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G7DIE
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Posts: 65




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« Reply #5 on: February 15, 2013, 11:43:19 AM »

The Sirio GainMaster is fibreglass for a reason, it supports a 5/8WL dipole inside, the elements of which are not grounded to any metallic part of the antenna, at the base of the antenna is a coax choke which helps eliminate common mode current Wink
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W5WSS
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Posts: 1683




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« Reply #6 on: February 15, 2013, 12:24:56 PM »

Yeah but the reasoning precludes the effects of a fibre glass exoskeleton relative to static charge vulnerability.

any material used as an exoskeleton to house an internal vertical antenna greatly increases the chances that equipment down inside the shack is at much greater risk by high discharges and emp  and always will be more problematic to charge potentials that exceed the discharge threshold along the fibre glass exoskeleton. NOT the internal antenna nor can grounding the internal antenna prevent such charges from developing on the outside exoskeleton. Problem is associated with the inability to safely Earth the outer shell.

The performance of the internal antenna was and never has been debated by me.
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G7DIE
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Posts: 65




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« Reply #7 on: February 15, 2013, 04:42:46 PM »

Yeah but the reasoning precludes the effects of a fibre glass exoskeleton relative to static charge vulnerability.

any material used as an exoskeleton to house an internal vertical antenna greatly increases the chances that equipment down inside the shack is at much greater risk by high discharges and emp  and always will be more problematic to charge potentials that exceed the discharge threshold along the fibre glass exoskeleton. NOT the internal antenna nor can grounding the internal antenna prevent such charges from developing on the outside exoskeleton. Problem is associated with the inability to safely Earth the outer shell.

The performance of the internal antenna was and never has been debated by me.


You didn't pose the original question, as a result I wasn't answering a question you didn't ask Huh You did however suggest the internal part of the antenna may be dc grounded, I'm confident you will now see this isn't the case Wink
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W5WSS
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Posts: 1683




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« Reply #8 on: February 16, 2013, 04:48:37 AM »

 Whether the embedded antenna is an end fed vertical, center fed balanced dipole or a variation is not anecdotal relative to the build up beyond discharge levels of the exoskeleton tube that occurs independently of the internal antenna.

Earthing the inside antenna will not prevent the Fiber glass support pipe from potentially lethal static build up beyond discharge another words a lightning strike.

In South Florida I have witnessed a fellow replace his fiber Glass antenna 4 times!
Pulverized it.

His other nearby metal verticals were always fine afterwards.
They were clamped to ground using a wander lead attached to a Earthing rod prior to the thunderstorms.

This anecdote is simply not possible with the fiber glass material way up in the sky because it can not be Earthed.

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RFRY
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Posts: 298


WWW

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« Reply #9 on: February 17, 2013, 04:39:17 AM »

The schematic available via the link in the OP shows that the upper arm of the dipole is isolated from any d-c ground by a series capacitor.  So any static charge on that conductor would have no known path to earth ground.

The conductors of a center-fed dipole comprise a balanced radiator, so no connection to earth ground is needed for it to radiate efficiently, assuming a good match of its feedpoint Z to the transmission line connected there.

A free-space NEC analysis of a 5/8-wave, vertical, center-fed dipole using conductors of 6.75 m total length and 25 mm OD shows a feedpoint Z of 189 +j 323 ohms at 27.75 MHz.  So the stub matching shown in their schematic would need to match values of that order to (unbalanced) 50 ohm coax.  The peak directivity of the NEC model is 2.45 dBi, and lies in the horizontal plane.

The directivity of the Sirio Gain-Master at 27.75 MHz is not shown at that link, because the radiation patterns there have been normalized.
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