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Old 08-12-2017, 06:41   #1
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Why $250 insulator?

For SSB backstay antenna service, why spend ($250 x 2) for stainless and delrin insulators when $15 porcelain will work?

Granted, you would need 7x19 cable and crimped Nico sleeves. If this type of insulator fails, the cables are left interlocked, so it's failsafe.
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Old 08-12-2017, 08:43   #2
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Re: Why $250 insulator?

I would think it would be that porcelain will shatter easily and you could loose the back-stay
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Old 08-12-2017, 08:48   #3
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Re: Why $250 insulator?

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I would think it would be that porcelain will shatter easily and you could loose the back-stay


If it did, it would slacken the backstay, but it won’t become disconnected.
My guess is it’s just not strong enough, the loads would crush one
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Old 08-12-2017, 08:50   #4
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Re: Why $250 insulator?

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I would think it would be that porcelain will shatter easily and you could loose the back-stay

They're failsafe. IF it breaks, the cables remain connected, although loosened by 3 inches.

Broadcast stations and Electric utilities have used these for years, and they very rarely fail ...

The only thing I can think of is they probably have more capacitance between the wire ends, but I would not expect that to be a big problem.
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Old 08-12-2017, 08:50   #5
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Re: Why $250 insulator?

Should be fine on boats under 30'
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Old 08-12-2017, 08:57   #6
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Re: Why $250 insulator?

The smallest (1 lb) types are rated at 10,000 lbs:

https://peakdemand.com/wp-content/up...Insulators.pdf
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Old 08-12-2017, 09:03   #7
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Re: Why $250 insulator?

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For SSB backstay antenna service, why spend ($250 x 2) for stainless and delrin insulators when $15 porcelain will work?
Porcelain insulators are not as strong as the rigging cable. They will crumble long before the wire breaks. I am not sure, but I think that the minimum safe bend radius for rigging cable is larger than the radius of the insulator.

When they are used in broadcast and electrical distribution applications, it is with a much softer galvanized steel cable that has a lower tensile strength and a smaller minimum bend radius.

Quote:

Granted, you would need 7x19 cable and crimped Nico sleeves. If this type of insulator fails, the cables are left interlocked, so it's failsafe.

No, it's not. Though the cables are interlocked, they will be bent at a sharp angle when force is applied. The sharp angle creates a considerable loss of strength, just as would happen when lifting a heavy load using cable without a thimble in the splice.
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Old 08-12-2017, 09:24   #8
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Re: Why $250 insulator?

At 10,000 pounds, it appears the insulator is stronger than 7x19 1/4" cable.

Clearly IF it failed, the two interlocked cables wouldn't be AS strong as original, but with reasonable care, the rig should not fail.
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Old 08-12-2017, 09:32   #9
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Re: Why $250 insulator?

My 1966 Pearson vanguard had those on the backstay. They’re fine for a smaller boat with overspecced rigging.

I would not do this to a modern boat with a highly loaded rig.
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Old 08-12-2017, 10:27   #10
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Re: Why $250 insulator?

This is a false economy. If the insulator breaks or cuts through, you stand a very good chance of losing the stay catastrophically.
This is because the bend radius of the line would be far too sharp to be anywhere near safe. A stay that is linked with another line without thimbles or something to hold a large turn radius is horribly weakened.
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Old 08-12-2017, 10:45   #11
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Re: Why $250 insulator?

You used to see them on boats all the time. So I guess they work! My gut always told me they would be fragile for some reason, but they are used on utility poles a lot. I guess the material is in compression from the wire not tension, That may be why they work well. What are the fancy marine ones made of anyway? Some type of plastic?
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Old 08-12-2017, 10:49   #12
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Re: Why $250 insulator?

Quote:
Originally Posted by Jammer View Post
Porcelain insulators are not as strong as the rigging cable. They will crumble long before the wire breaks. I am not sure, but I think that the minimum safe bend radius for rigging cable is larger than the radius of the insulator.

When they are used in broadcast and electrical distribution applications, it is with a much softer galvanized steel cable that has a lower tensile strength and a smaller minimum bend radius.
The steel cable may be just as hi tensile strength as SS cable.It depends

No, it's not. Though the cables are interlocked, they will be bent at a sharp angle when force is applied. The sharp angle creates a considerable loss of strength, just as would happen when lifting a heavy load using cable without a thimble in the splice. That doesnt mean they will break immediately. In fact if the insulator fails the rig tension will likely decrease .
hmmmm

1X19 Strength
Diameter Galvanized Stainless

1/4" 8,200 8,200
9/32" 10,300 10,300
5/16" 12,500 12,500
3/8" 17,500 17,500
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Old 08-12-2017, 11:49   #13
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Re: Why $250 insulator?

The truth is that you don't even need insulators for a backstay antenna. There are antenna designs that use grounded radiators that employ a shunt or parallel feed.

What I use is a ground backstay with the feed line connected to the backstay between 7 to 8 feet above the deck. No insulator are required at either the lower or upper ends of the backstay.

Since purchasing Feeling Good in 1978 I have used this antenna configuration for both Ham and SSB operations. The performance of this antenna has never come into question. Being grounded it tends to be low noise on receive. On transmit it has never failed to be heard by any station that I can receive.
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Old 08-12-2017, 13:04   #14
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Re: Why $250 insulator?

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Originally Posted by Viking Sailor View Post
The truth is that you don't even need insulators for a backstay antenna. There are antenna designs that use grounded radiators that employ a shunt or parallel feed.

What I use is a ground backstay with the feed line connected to the backstay between 7 to 8 feet above the deck. No insulator are required at either the lower or upper ends of the backstay.

Since purchasing Feeling Good in 1978 I have used this antenna configuration for both Ham and SSB operations. The performance of this antenna has never come into question. Being grounded it tends to be low noise on receive. On transmit it has never failed to be heard by any station that I can receive.


It's certainly possible to do that, but depending upon how well all conductors are additionally bonded, the insulated backstay has a greater potential for impedance stability under windy and wet conditions.

Many AM broadcast stations use a grounded tower antenna with a wire skirt feed system - known as a folded unipole. I've tuned and troubleshot many of them. The conventional approach is to insulate the entire tower on a large porcelain insulator and feed it at the top of the insulator.

They both perform about the same, but the folded unipole allows easier additions of (money-making) antennas on the tower. The downside of the unipole is that bonding of all attached conductors is critical for stability, and is the most common cause of failure.
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Old 08-12-2017, 13:27   #15
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Re: Why $250 insulator?

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Originally Posted by Viking Sailor View Post
The truth is that you don't even need insulators for a backstay antenna. There are antenna designs that use grounded radiators that employ a shunt or parallel feed.

What I use is a ground backstay with the feed line connected to the backstay between 7 to 8 feet above the deck. No insulator are required at either the lower or upper ends of the backstay.

Since purchasing Feeling Good in 1978 I have used this antenna configuration for both Ham and SSB operations. The performance of this antenna has never come into question. Being grounded it tends to be low noise on receive. On transmit it has never failed to be heard by any station that I can receive.
Viking Sailor, would you mind putting up a diagram of that antenna design?
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