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Antenna Question

Old 01-06-2003, 01:59 AM
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Question #1: Digital Antennas model 529VW or Shakespeare SH-5225-FLT with a intermode filter

#2: What is an INTERMODE FILTER?

Thanks!
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Old 01-06-2003, 03:19 AM
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Boat Guy-

I believe it is Intermod (spelling) which is a shortened spelling for intermodulation. That is the same antenna I just replaced on my boat.

That is basically a built in "noise filter". It is supposed to cut down all the squeals and squawks caused by heavy traffic. It is also supposed to filter out the signal noises generated by pagers, and other FM radio signals that are near the marine frequencies.

On a busy weekend or typical mid summer day, I did not notice any diiference in the filtering effect. I still heard all the weird noises. As a matter of fact, I will swear that the receive sensitivity and strenghth was hampered by it. I did a side by side comparison of a regular Galaxy antenna using my radio on my friend's boat (very similar boat and mounting characteristics). I will swear that I "heard" better on his plain Galaxy. He broke it about a month later and replaced it with a DIGITAL.

The DIGITAL is THE antenna to get! What a difference!

TSLTW

[This message was edited by Big E on 01-09-03 at 05:45 AM.]
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Old 01-06-2003, 02:20 PM
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So Digital is better than Shakespeare?
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Old 01-06-2003, 02:36 PM
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At least at 8 foot and under. I'm not sure what is better for a battle wagon with 16 foot capability. Haven't had the need to get one that big for now!

Wanna buy my old SH- 5225-FLT? Was going to use it to stake my tomatoes in the summer!

Only kidding, will use it for a backup.

TSLTW
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Old 01-06-2003, 02:44 PM
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I'm using a 5399 for my main radio right now and to tell you the truth if it were to break tomorrow I don't know if I just might buy another one to replace it rather than go with a Digital. Aside from being a bit on the heavy side I like it just fine. I'm also using a 5225 on my backup radio, but if it broke I'd replace it with a Digital 529VW in a heartbeat.

Thom

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Old 01-06-2003, 03:33 PM
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Thom-
What do you like about the 5399?
Is it a different design? I can see that you are not particularly impressed with the 5225 either, so what is 'special' about the 5399?

TSLTW
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Old 01-06-2003, 03:40 PM
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Intermodulation can only happen in a nonlinear device. Since the antenna in a linear component a intermodulation filter would nothing to its characteristics.
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Old 01-06-2003, 03:53 PM
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The 5399 is considerably different than the 5225. For one thing its a foot and a half longer at 9.5 feet and its a so a two part antenna, with the top section being smaller, lighter and the shorter of the two (its about the same as a typical 4' whip). The bottom section is very heavy and quite strong, if a bit inflexible. Anyway it works well and the extra length is good for a mile or so of extened range. If you can handel an 8 foot antenna it shouldn't be a problem. I've also noted that my SWR on it comes in right at 1.0 and I've never had a reading that good out of a 5225 or a 529VW.

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Old 01-06-2003, 04:16 PM
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I'm not trying to pick a fight or anything. But I would suggest that it cannot have a VSWR of 1. That would indicate a perfect antenna, and well, there just isnt any.

Consider this, the wavelength of the transmitted signal varies as the vhf channels are selected. Yet the antenna never changes length.
So there will be the one channel that standing waves are minimized, (the one where the effective length of the antenna is best matched to the wavelength of the transmitted signal) but all others will get worse.
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Old 01-06-2003, 08:52 PM
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Does anyone know of a good source (good price) for the Digital Antenna 553-VW? Defender and Bethel Marine list the 529 for a price but don't list the 553 at all.

553 covers a wider range so it can also be used for 2m Ham

Bill Smith
N2ASA
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Old 01-07-2003, 02:08 AM
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OK, let me ask another stupid question.

If I went to the respective websites for both
Digital Antennas model 529VW and Shakespeare SH-5225-FLT, what in the specifications would lead me to believe that one antenna is superior?

Sorry guys. Just trying to learn so I can figure things out for myself.
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Old 01-07-2003, 03:05 AM
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Outside of the fact that the Shakespeare has a 30 watt power handling rating, and the Digital is rated @ 100 watts, I wouldn't be able to point to anything specific.

I don't know if it applies to fm vhf broadcasting, but years ago, when CB was a popular craze, you looked for the antenna with the higher power handling. It usually meant it was a more efficient and better constructed antenna that was able to handle the numerous ILLEGAL power loads (linear amplifiers) that were popular.

Seeing the 2 antennas, side by side, is a different story. The Digital has a more "finished" look and the quality of assembly and components is better. The outside finish looks thicker and glossier. Soldered connections are neater, cleaner and solid.

Actual performance in the field is better, from my first hand observatiion. I witnessed the difference in the 2 when my friend replaced his Shakespeare with a Digital.

And Digital was chosen as the NMEA's Marine Antenna of the year for 2002.

TSLTW
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Old 01-07-2003, 08:31 AM
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Actually SWRs of 1.0 are not that uncommon. All it takes is an antenna length that exactly matches the wave length for a particular frequency. Of course with different channels (frequencys) available any antenna will be a better match at some frequencys compaired to others. The range of frequencys available on our VHFs is from a low of 156.025 MHz on USA channel 1 to a high of 157.425 on 88Alpha. So the mid point frequency is 156.725, which happens to correspond to channel 74. Do your SWR checks there and life is good. Of course most guys will use channel 16 when doing the SWR check, and that is a good one to use because it is very close, at 156.800, to the midpoint.

Thom

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Old 01-07-2003, 10:44 AM
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Bandwidth is also a good indicator. The larger, the better.
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Old 01-07-2003, 10:48 AM
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You will not find a VSWR of 1.0, ever, it is not physically possible.

quote: Every Digital Antenna marine antenna is tuned for minimum standing wave ratio (SWR) which approaches 1:1

the quote came from here...
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Old 01-07-2003, 02:12 PM
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Sea Dad,
As you stated, "there is no such thing as a perfect antenna" in a way you are right but I have to disagree on there is no way a 1.0 swr.

I feel that if an antenna is cut to the center of a band of frequencies, say for example the center of 150 mhz-170 mhz, which is 160 mhz.

Being that all is in good condition.......wire,connections,antenna,etc. if I cut the antenna for 160 mhz I feel somewhere along the frequencies of 150-170 the antenna is going to be 1.0.

I also feel that swr readings panic some people when they see it up near 1.7,2.0 to 1.....I don't think it matters that much UNLESS it is way out of wack and something is shorted........then time to repair or replace.

I admit that I start to look into the system if the swr is 2.0 to 1 though.
I feel that half the power that is going up the antenna is coming back down.
Not an EE here just a tinker'er of antennas.

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Old 01-08-2003, 01:11 AM
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First, I just wanted to say thanks for all those who took time to reply. The Long Island Boat show is
coming in Feb. I want to do my homework and get prices. Therefore I know what I want to get and what I want to pay BEFORE the show. If there are no good deals there, I can always go to the electronic vendors recommended in previous posts.

One last question: THE MOUNT!
Does it afect antenna performance? From reading
other posts, a Stainless Steel mount is cheap and the way to go. Plastic is cheaper and seems to be something to be avoided. Correct?
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Old 01-08-2003, 03:08 AM
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Booby Trap, yes you are right about having a 1.0 on a specific freq. thoretically. I had said that in my first reply, but failed to point it out again in my second one. Sorry I didnt mean to imply that it couldnt be had ever (poor choice of words).

I was still chasing the 2 real reasons you couldn't.
The first mainly of never working on a single frequency. If all you ever did was talk on 16 as the CG does, then sure you could get 1.0, but we as boaters dont. As soon as you get of the freq. they tuned it for minimum SWR's for it goes up.

The second reason you won't get 1.0...

Notice the specs for the antennas, even digital's, none of them are rated for 1.0, why, because its way too hard to get there, and not economical for them to chase it. They couldnt sell us a $1000 antenna for the boat eh?

All the tuning is done in the antenna itself, you can't help tuning by tweaking the cable length as in CB's.

So what does it all mean?

Find an antenna with the lowest rated VSWR closest to your freq. of choice (chan 16 or your working chan), then get the one with the highest bandwidth. The bigger the better.
Think of the bandwidth relating to power transmitted as a tupperware bowl upside down. The flat bottom part is the width of the bandwidth, as soon as you get outside that width, the power output goes down (the sides of the bowl), and quickly. You dont have to get very far away to be transmitting nothing.
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Old 01-08-2003, 03:13 AM
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Boat Guy, Choice of mount is up to you, the performance of the antenna wont be affected that much, unless it wobbles all over the place.

Stainless is the way too go though. Much more rigid, the antenna will not rock nearly as much. Plus you just spent a bundle on the mega antenna, dont put a weak link in the system now.
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Old 01-08-2003, 05:29 AM
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Just a bit that maight be of interest to you on the mounts. First off, as your correctly have assumed, the plastic mounts should be avoided. They tend to fail, more from falling antenns than from actually breaking. but fail none the less.

Now what I wanted to say. The antenna I am using right now is heavy. Its a Shakespeare 5399 and as a guess I'd say it outweighs the more common 5225 or 529VW by about half. I have had two stainless steel mounts break in the last year and a half now. I switched back to chromed bronze mounts, mostly because they are considerably more hefty (and I knew that the stinless ones didn't work), and I haven't had a failure since. Of course I never had a stainless one fail with the typical 8' antennas either. Anyway it has come to be my assumption that the stainless mounts are being taxed into duty that is just about at the limit of their capability in a normal application. Just something to think about. The down side to the chromed bronze ones is that after a few years they pit and become unattractive.

Thom

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