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Old 01-10-2013, 06:31   #121
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Re: Amazing Power of Good Antennas

Jan,
You're welcome!!

And, Dan is 100% correct on this point....
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Originally Posted by transmitterdan View Post
Probably the AIS was not damaged by the SSB antenna. Powering the AIS off won't make it less susceptible to damage.
While I also cannot fathom your HF transmitter was the cause of your AIS250's troubles, please understand that powering the AIS250 OFF will do nothing to protect it from input damage...

Fair winds....

John
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Old 03-10-2013, 16:48   #122
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Re: Amazing Power of Good Antennas

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Originally Posted by btrayfors View Post
There's no "skip" going on. It's tropospheric ducting AKA "Tropo" pure and simple.
I've found my radio "handle". From now on, you'll know me as

Skip Tropo
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Old 20-10-2013, 03:59   #123
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Re: Amazing Power of Good Antennas

John and/or Dan,

"the last one for the road"

If I do want to protect the AIS receiver entry stages (with AIS powered on or off), and without the use of a high-pass filter, I guess I would do that with:

- a 2 way coaxial (antenna) switch bewteen the AIS antenna and the AIS unit, one that puts the unused output to ground, or by shorting the second output (PL259 with inner pin and casing shorted)
- and switching the AIS to this shorted output whenever I want to use the SSB?

Jan
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Old 20-10-2013, 05:25   #124
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A simple on/off coaxial switch is sufficient. There is no need to ground the AIS receiver input in my view. If you want to it would be ok to use a simple 2-way coaxial switch. Connect the antenna to input 1 and a 50ohm 5Watt termination on input 2. Connect the AIS transceiver to C (common). Then you don't have to remember to turn off AIS transmissions while using SSB.
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Old 20-10-2013, 10:34   #125
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Re: Amazing Power of Good Antennas

Thanks Dan.

But my AIS is only AIS receiving. So a 50 Ohm termination wouldn't be necessary but still probably a better idea than just a short over input 2.

Jan
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Old 20-10-2013, 19:53   #126
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Re: Amazing Power of Good Antennas

Jan,
First off, I agree with Dan that switching into a 50-ohm load is much better than into a "short" (as transients and radiated stray HF RF can still flow along the outside of coaxial shields, or any conductor nearby)....


But, I really think you're worrying for nothing (yes, I'm aware of your earlier failed Raymarine AIS, but it is VERY unlikely that this failure was caused by HF RF ingress)

I've written before about the math / proof of what the isolation is....and also the fact I've ran ~ 1500 watts on HF (10-12 db more than you've got on your boat), with VHF antennas just a couple feet away, connected to sensitive vhf radios, with never an issue...
{the only time I've ever had a "receiver issue" was actually my own fault....I TRANSMITTED > 1100 watts on 144mhz INTO a 144mhz tower-mounted RECEIVE pre-amp..as a screwed-up my pre-amp switching/sequencing when using my 4-yagi, 2m moonbounce array on some meteor-scatter contacts....but again this was transmitting > 1100 watts directly into a low-noise GasFET tower-mounted pre-amp...}

Further, myself and 100's / 1000's of others, have stern-rail-mounted AIS antennas which are just a couple feet (< 1 meter) from our HF backstay antennas....and never an issue...

So, while I understand your concern / hesitation.....even if you don't wish to believe the math, nor my experiences, think about why would anyone design, build, and sell a radio (AIS, VHF, receiver, etc.) that is supposed to be installed near other radios, but would sustain damage if it was so installed???
It just doesn't make sense, neither business-wise nor electronics-wise...
(and if this was a issue with the AIS250, we'd certainly hear of 100's of failures, which I haven't seen/heard...)



Just my thoughts...
I hope this helps...one last shot, for the road...


John
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Old 21-10-2013, 01:31   #127
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Re: Amazing Power of Good Antennas - AIS

Thanks for the reassurance, John.

Well it is that the problem seems to have started when I installed the stern-rail mounted dedicated AIS antenna and stopped using the masttop VHF antenna and the on-board splitter of the AIS-250.

Also the AIS250 installation manual warns to "install the AISis blackbox 1 to 2 metres away from other transmitters...

Could it be poor design, poor filtering, poor shielding?

It is just a circuit board in a plastic casing.... I did install supression ferrites on all in/outgoing wires but I probably did it after the problems started.

Maybe it was just just bad luck.

I do have to say that my SSB causes the "Xmas tree" lighting of panel lights even when I did everything to avoid ground loops and paid close attention to the RF ground.
Also a Mu-61 toroid with 10 turns of the input coax and the feed wires just at the SGC-230 atu.

If that replacement AIS250 decides to get "sick" again, I'll throw it out and install an Icom one.

Jan
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Old 31-01-2014, 14:53   #128
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Re: Amazing Power of Good Antennas

Are there any Monohulls using the Digital 4 foot - 4.5db VHF Antenna at the Masthead?

4 ft VHF Marine Antennas- 4.5dB Gain

My research indicates that the Digital antenna is a "cut above" the Shakespeare Galaxy 5400 XT...

5400-XTM Little Giant

Practical Sailor gave high marks to Digital Antennas - being very well made:

http://www.practical-sailor.com/news...TED_INSIDE.pdf

http://www.practical-sailor.com/news...AL_GADGETS.pdf

Marine VHF Antenna Test - Practical Sailor Article

3dB VHF Antenna Test - Practical Sailor Article

My only concern is whether it would be a problem for 4.5db vs 3db at the masthead...?

Thanks in advance!
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Old 31-01-2014, 16:04   #129
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Re: Amazing Power of Good Antennas

Quote:
Originally Posted by Capt'n Ricko View Post
Are there any Monohulls using the Digital 4 foot - 4.5db VHF Antenna at the Masthead?

4 ft VHF Marine Antennas- 4.5dB Gain

My research indicates that the Digital antenna is a "cut above" the Shakespeare Galaxy 5400 XT...

5400-XTM Little Giant

Practical Sailor gave high marks to Digital Antennas - being very well made:

http://www.practical-sailor.com/news...TED_INSIDE.pdf

http://www.practical-sailor.com/news...AL_GADGETS.pdf

Marine VHF Antenna Test - Practical Sailor Article

3dB VHF Antenna Test - Practical Sailor Article

My only concern is whether it would be a problem for 4.5db vs 3db at the masthead...?

Thanks in advance!
Vertical beam width will be slightly tighter then 3db , but nothing you'd notice.

Dave
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Old 02-02-2014, 07:55   #130
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Re: Amazing Power of Good Antennas

Quote:
Originally Posted by Capt'n Ricko View Post
Are there any Monohulls using the Digital 4 foot - 4.5db VHF Antenna at the Masthead?

4 ft VHF Marine Antennas- 4.5dB Gain

My research indicates that the Digital antenna is a "cut above" the Shakespeare Galaxy 5400 XT...

5400-XTM Little Giant

Practical Sailor gave high marks to Digital Antennas - being very well made:

http://www.practical-sailor.com/news...TED_INSIDE.pdf

http://www.practical-sailor.com/news...AL_GADGETS.pdf

Marine VHF Antenna Test - Practical Sailor Article

3dB VHF Antenna Test - Practical Sailor Article

My only concern is whether it would be a problem for 4.5db vs 3db at the masthead...?

Thanks in advance!
I installed one on my masthead, along with LMr400 ulraflex. Am I pleased? Sort of. I spent the last two months thinking that my installation was crap and I was getting interference from my LED masthead lights. It turns out that it is the opposite... that other people have crap VHF setups, or more to the point, they have "normal" configurations. While they can clearly hear me from a long distance, I cannot hear them. So, I am generally pleased but not sure it was worth the added expense.

Couple items of note:

1) This type of antenna requires a substantial mount... mounts that would cause pretty severe damage if/when the antenna makes contact with an overhead structure and the antenna doesn't break first.

2) The 5400 XT comes with a pigtail wire already attached. This means you need to install an additional connection between the antenna and the wire. I don't know how much actual difference it makes but depending on the quality of the connection, it could be substantial and negate a DB or two.

With that said, I have started seeing a growing number of boats out here with them installed on the masthead.
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Old 02-02-2014, 12:37   #131
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Re: Amazing Power of Good Antennas

The pigtail is not such a bad idea. After all, it means you can replace the coax in a timely manner (i.e. every 5 years?) without having to do any cutting and splicing aloft. As long as there's room to snake a pre-terminated cable up the mast, it would make life very simple for installation the first time as well. And, for quickly swapping out a possible bad cable to confirm if that was a problem.

Not an altogether bad way to go.

Now how tow "four foot whips" can differ from 3db to 4.5db in gain, when the only(?) difference is potting the base loading coil on one, I don't know. I'm real curious about that, maybe one of our professional sparkies could comment on that?

Are they just playing "the db game" measuring different gains?
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Old 02-02-2014, 13:00   #132
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Re: Amazing Power of Good Antennas

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The pigtail is not such a bad idea. After all, it means you can replace the coax in a timely manner (i.e. every 5 years?) without having to do any cutting and splicing aloft. As long as there's room to snake a pre-terminated cable up the mast, it would make life very simple for installation the first time as well. And, for quickly swapping out a possible bad cable to confirm if that was a problem.

Not an altogether bad way to go.

Now how tow "four foot whips" can differ from 3db to 4.5db in gain, when the only(?) difference is potting the base loading coil on one, I don't know. I'm real curious about that, maybe one of our professional sparkies could comment on that?

Are they just playing "the db game" measuring different gains?
Nah. It's probably just a 5/8 wavelength vertical instead of a 1/2 wave vertical. These exhibit about 1.5db gain over the 1/2 wave vertical.

Does this make any difference? Maybe a tiny bit, but as indicated earlier in this thread the "gain" comes with some attendent drawbacks.

I'd stick with the tried and proven "3db gain" traditional VHF antenna. Mine is about 20 years old and is still working great.

Bill
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Old 02-02-2014, 13:14   #133
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Re: Amazing Power of Good Antennas

" just a 5/8 wavelength vertical instead of a 1/2 wave "

Offhand...39" wavelength in metal? So about 5" per 1/8th wave? I guess one of them is measuring their 40" in Imperial Inches then.

Both seem well-made, in the long run I guess the big question is "Can I get that to match my sailcovers?" (WEG)
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Old 02-02-2014, 14:37   #134
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Re: Amazing Power of Good Antennas

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" just a 5/8 wavelength vertical instead of a 1/2 wave "

Offhand...39" wavelength in metal? So about 5" per 1/8th wave? I guess one of them is measuring their 40" in Imperial Inches then. ......
...." (WEG)
???

1/2 wavelength @ 156.8mHz (Channel 16) is 2.985 feet

5/8 wavelength @ 156.8mHz is 3.730 feet

Close enough to 3' and 4', respectively!

Unless my math is way off :-)

Bill
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Old 02-02-2014, 22:03   #135
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Re: Amazing Power of Good Antennas

No, that's my math being off, Bill. I was thinking 19-1/2" or so as a starting point but that's just 1/4 wave, somewhere I mistook that for half.

But as you say, close enough to 3' and 4', where both antennas say 4 feet. So at some point, there's a rubber ruler involved?
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