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  #177  
Old 04-11-2011, 12:53 PM
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eddie,
its very easy to hear and see when theres multipath on fm, local signals flutter at a time varying rate, they hit a peak then flutter back to where they usually are with a woosh wooosh woooosh sound as the multiple paths arriving at different phase angles sum and cancel each other,

on ssb the effect is similar to the effect you get when switching the polarity of one loudspeaker on a hifi cancelling the bass frequencies but its not switched, it is a variable in and out of phase sound.
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  #178  
Old 04-11-2011, 01:06 PM
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Originally Posted by bob85 View Post
eddie,
its very easy to hear and see when theres multipath on fm, local signals flutter at a time varying rate, they hit a peak then flutter back to where they usually are with a woosh wooosh woooosh sound as the multiple paths arriving at different phase angles sum and cancel each other,

on ssb the effect is similar to the effect you get when switching the polarity of one loudspeaker on a hifi cancelling the bass frequencies but its not switched, it is a variable in and out of phase sound.
Thanks Bob, something rings a bell. You probably described that to me before, but sometimes my recall is not up to par. Do you hear something similar on AM or FM? I would think you probably would, right?
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  #179  
Old 05-21-2011, 08:53 PM
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Default I just read up on this thread, thanks...

I just read up on this thread, thanks for the continued input plots showing top hats, Marconi. I for one have just compared my originally 80" MM antenna to a modified version that I made and have found no discernable difference in signal in a two mile low power test on TX vs. full length whip. I did the test at 2 miles with 50 ft. elevation rise to target receiver. Furthermore, there is simply no difference in the performance to the places I normally talk, about 50miles groundwave over hilly terrain and the skip that I shoot to the U.S. and the Islands. My top hat replaces about 35" of radiator while the massive 5 wrap center coil replaces about 26" of a full quarterwave radiator. This antenna is impossible to tell apart in performance from my 9 ft whip, and I am attempting to identify ways to alter its vertical pattern response to more favor the use that I require.
Clearly your models show vertical pattern modification by top hat implementation. There are more factors that need to realized, such as at what size of top hat would be optimal to yield the best vertical pattern, interactions with earth by implementation of various height and form hats, etc. Perhaps a model of the Immortal is an important next step as is modeling my own version of it.

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Originally Posted by Marconi View Post
Here are several of the more important 1/4 wave antennas with the pattern overlaid and compared.

The legend at the left:
#4 is the antenna with all 108" whip elements that are horizontal- dark blue
#5 has no radials at all - green
#6 is the best antenna modeled using all 102" whip elements - red
#10 is the antenna with a Top Hat - lite blue

Attachment 4484

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  #180  
Old 05-22-2011, 09:33 AM
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Originally Posted by 76Q View Post
I just read up on this thread, thanks for the continued input plots showing top hats, Marconi. I for one have just compared my originally 80" MM antenna to a modified version that I made and have found no discernable difference in signal in a two mile low power test on TX vs. full length whip. I did the test at 2 miles with 50 ft. elevation rise to target receiver. Furthermore, there is simply no difference in the performance to the places I normally talk, about 50miles groundwave over hilly terrain and the skip that I shoot to the U.S. and the Islands. My top hat replaces about 35" of radiator while the massive 5 wrap center coil replaces about 26" of a full quarterwave radiator. This antenna is impossible to tell apart in performance from my 9 ft whip, and I am attempting to identify ways to alter its vertical pattern response to more favor the use that I require.
Clearly your models show vertical pattern modification by top hat implementation. There are more factors that need to realized, such as at what size of top hat would be optimal to yield the best vertical pattern, interactions with earth by implementation of various height and form hats, etc. Perhaps a model of the Immortal is an important next step as is modeling my own version of it.

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SoCal 76, Fast4Socal76 etc etc etc you sure change your name alot of these forums ...

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  #181  
Old 05-22-2011, 11:42 AM
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76Q, here are some variations for radiator and top hat lengths for a 1/4 wave radiator. I used slanted down radials and one model that is full length and slanted down radials, and one model that is full 1/4 wavelength using 4 x 108" horizontal ss radials.

I also have a model of a simulated mobile, but I don't think the pattern is near what you might expect, so I didn't include it. I'm not even sure it is a good model. It shows to be workable however. I used the 4 horizontal radials and made 2 x 6" x 4' and 2 x 6" x 8'. I will work with it a bit and if it looks promising, I post it later. This may prove to be futile however, because mobiles have a very unpredictable ground plan with variations and curves that are irregular and may be difficult for me to model.

The numbers at the end of the captions are the length in inches for the radiator and the top hat including a little space for the feed point hub.

Top Hats various sizes.pdf
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  #182  
Old 05-22-2011, 11:56 AM
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anybody ever seen a top-hat on a commercial television or radio broadcasting antenna ?
i haven't , but i'm guessing the station and their advertisers want to reach every potential customer . if a top-hat will increased their broadcasting range or decrease the wind load and keep the same performance why wouldn't they use them ?

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  #183  
Old 05-22-2011, 12:15 PM
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Originally Posted by BOOTY MONSTER View Post
anybody ever seen a top-hat on a commercial television or radio broadcasting antenna ?
i haven't , but i'm guessing the station and their advertisers want to reach every potential customer . if a top-hat will increased their broadcasting range or decrease the wind load and keep the same performance why wouldn't they use them ?
No I haven't, because cap hats serve on in the receive stage of antennas performance right? so why would they need one?

It may help the antenna to think it's longer than it is and really serves no purpose in the antennas tx performance or they would have them on a 102'' whip.

Is someone gonna make an issue of the coronal ball being a form of cap hat?

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  #184  
Old 05-22-2011, 12:25 PM
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Originally Posted by BOOTY MONSTER View Post
anybody ever seen a top-hat on a commercial television or radio broadcasting antenna ?
i haven't , but i'm guessing the station and their advertisers want to reach every potential customer . if a top-hat will increased their broadcasting range or decrease the wind load and keep the same performance why wouldn't they use them ?
I used to run a station on 1450 KHz that had an eight foot diameter top hat.The station originally went on the air in 1945 just after the war and the antenna was a 96 foot high 4 inch diameter steam pipe with four parallel lengths of #6 copper wire running the length to aid in continuity.The top hat was referred to as the bicycle wheel at the top. The top hat was to add extra loading to the short antenna and make it easier to tune and a bit more broadbanded. In 1986 we moved he TX site and put up a proper 1/4 wave single tower for an antenna. While the 96 foot mast was not all that ideal for 1450 KHz in an area rapidly growing up with houses it did work like a charm on 80m and 160m before we took it it down after having activated the new site. It now continues to work rather well as a couple clothesline poles and an axle or two as well as a pole or two for a couple homemade trailers.

Many AM sites on the low end of the band used top hats and most longwave antennas or VLF antennas are actually vertical wire antennas with a single long horizontal wire that functions as a cap hat and does very little radiating.
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