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Base Sirio 2008 vs 2016
- Thread starter Greg T
- Start date
regarding radial ground systems and loss resistance.
http://www.w3pga.org/Antenna Books/Reflections III.pdf
chapter 1, page 6, section (7)-(1) to the end of (7)-(1)
a collection of the most accurate information regarding
transmission lines and antennas. (152 MB. download).
http://www.w3pga.org/Antenna Books/Reflections III.pdf
chapter 1, page 6, section (7)-(1) to the end of (7)-(1)
a collection of the most accurate information regarding
transmission lines and antennas. (152 MB. download).
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(1) A ground system having a hundred properly
installed radials has negligible loss resistance (Ref
20). AM broadcast stations operating in the 540- to
1600-kHz band use either 120 or 240 radials, while
the FCC requires a minimum of 90. With such a
ground system the terminal impedance of a thin
quarter-wave (X/4) vertical is approximately the
theoretical value of 36.5 + y'22 ohms, and becomes
approximately 32 ohms resistive when the antenna
is shortened to resonance. Thus, when fed with a
50-ohm line, the SWR at resonance will be close to
1.6, rising predictably on either side of resonance.
However, a ground system having only 15 radials
has approximately 16 ohms of ground-loss resistance
with this antenna. Thus, if we remove a few
radials at a time from the 100-radial system, the
increasing ground (loss) resistance adds to the
fixed radiation resistance, increasing the total
resistance terminating the feed line. Hence, as each
radial is removed, the terminating resistance comes
closer and closer to 50 ohms, reducing the SWR.
When enough radials have been removed for the
ground-loss resistance to reach 18 ohms, the terminating
resistance will be 18 + 32 = 50 ohms, for a
perfect one-to-one match! While the SWR went
down, though, so did the radiated power, because
now the power is dividing between 32 ohms of radiation
resistance and 18 ohms of ground resistance!
In cases where losses are very small, it is unnecessary
to improve an impedance mismatch that produces an
SWR of only 1.6:1, because only a 0.24 dB
increase in power will result by reducing the 1.6:1
mismatch to 1:1. However, in this antenna situation,
reducing the 1.6:1 mismatch to 1:1 by removing
radials will cause a 36% decrease in radiated power,
a loss of 1.93 dB in the ground resistance.
Ground resistance with 100 to 120 radials is typically
in the range of 1 to 2 ohms, or less. However,
ground systems having from two to four radials may
have a loss resistance as high as 30 to 36 ohms, so
now the SWR at the resonant frequency will be
around 1.3 or 1.4. However, when operating at other
frequencies, instead of rising from this low value of
SWR, as it should at frequencies away from resonance,
the ground-loss resistance holds the off-resonant
SWR to lower values than would result with a
good ground. The low SWR simply indicates that
the line is well matched, but it offers no clue that
approximately half the power is heating the ground.
Thus, the low SWR in this case is misleading;
instead of verifying that the antenna system is efficient
over a wide frequency band, it is actually
telling us that the efficiency is very poor indeed!
here's the simple, non-technical explanation. the
larger the number of radials used, (to collect the
current radiated by the antenna) the lower the
loss resistance, the higher the radiation efficiency
and the better the performance, both in xmit and
rcve, according to the principle of reciprocity.
installed radials has negligible loss resistance (Ref
20). AM broadcast stations operating in the 540- to
1600-kHz band use either 120 or 240 radials, while
the FCC requires a minimum of 90. With such a
ground system the terminal impedance of a thin
quarter-wave (X/4) vertical is approximately the
theoretical value of 36.5 + y'22 ohms, and becomes
approximately 32 ohms resistive when the antenna
is shortened to resonance. Thus, when fed with a
50-ohm line, the SWR at resonance will be close to
1.6, rising predictably on either side of resonance.
However, a ground system having only 15 radials
has approximately 16 ohms of ground-loss resistance
with this antenna. Thus, if we remove a few
radials at a time from the 100-radial system, the
increasing ground (loss) resistance adds to the
fixed radiation resistance, increasing the total
resistance terminating the feed line. Hence, as each
radial is removed, the terminating resistance comes
closer and closer to 50 ohms, reducing the SWR.
When enough radials have been removed for the
ground-loss resistance to reach 18 ohms, the terminating
resistance will be 18 + 32 = 50 ohms, for a
perfect one-to-one match! While the SWR went
down, though, so did the radiated power, because
now the power is dividing between 32 ohms of radiation
resistance and 18 ohms of ground resistance!
In cases where losses are very small, it is unnecessary
to improve an impedance mismatch that produces an
SWR of only 1.6:1, because only a 0.24 dB
increase in power will result by reducing the 1.6:1
mismatch to 1:1. However, in this antenna situation,
reducing the 1.6:1 mismatch to 1:1 by removing
radials will cause a 36% decrease in radiated power,
a loss of 1.93 dB in the ground resistance.
Ground resistance with 100 to 120 radials is typically
in the range of 1 to 2 ohms, or less. However,
ground systems having from two to four radials may
have a loss resistance as high as 30 to 36 ohms, so
now the SWR at the resonant frequency will be
around 1.3 or 1.4. However, when operating at other
frequencies, instead of rising from this low value of
SWR, as it should at frequencies away from resonance,
the ground-loss resistance holds the off-resonant
SWR to lower values than would result with a
good ground. The low SWR simply indicates that
the line is well matched, but it offers no clue that
approximately half the power is heating the ground.
Thus, the low SWR in this case is misleading;
instead of verifying that the antenna system is efficient
over a wide frequency band, it is actually
telling us that the efficiency is very poor indeed!
here's the simple, non-technical explanation. the
larger the number of radials used, (to collect the
current radiated by the antenna) the lower the
loss resistance, the higher the radiation efficiency
and the better the performance, both in xmit and
rcve, according to the principle of reciprocity.
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I think it is a stretch to call it "non-technical", given the very low bar that some people consider what is and isn't "technical", and I think this is a tough concept for many to wrap their heads around, but it is correct.
I would also direct you to chapter 5 of the freely available "Another Look at Reflections" pdf file, a chapter called "to low an SWR for the wrong reasons" or chpater 5 of the same book in freecell's link above, which is broken on my end at the space, which is just an updated version of the same text.
To get freecell's link to work you have to copy and paste the entire link into the address bar, at least in the firefox browser. Its a good book, and I suggest actually purchasing it rather than using the free download as it is still in print.
The DB
I would also direct you to chapter 5 of the freely available "Another Look at Reflections" pdf file, a chapter called "to low an SWR for the wrong reasons" or chpater 5 of the same book in freecell's link above, which is broken on my end at the space, which is just an updated version of the same text.
To get freecell's link to work you have to copy and paste the entire link into the address bar, at least in the firefox browser. Its a good book, and I suggest actually purchasing it rather than using the free download as it is still in print.
The DB
"try right clicking the link and left click "open in new tab."
Interesting info, indeed. Kinda makes me wonder now why this antenna is much more wide-banded than the sigma I removed, and IF it's a good thing or not. Regardless of why, I'm not able to do anything about it, anyway. I'm using LMR240 feed with a meter, an amp and a low pass filter in line. Currently, after raising the antenna into position, 26.965 doesn't even move the SWR needle, and 27.705 climbs to 1.1:1. I have not checked how low or high I can go to get 1.5:1. I will have to study that info a bit, tho. Time for this old codger to learn something
I hear you Greg T,
I just happen to be moving my radio setup to a different wall, 15 feet from current location. This location is where my detached garages underground electrical panel is mounted to the building. Very good timing for this thread to come up! Very interesting info.
I just happen to be moving my radio setup to a different wall, 15 feet from current location. This location is where my detached garages underground electrical panel is mounted to the building. Very good timing for this thread to come up! Very interesting info.
Then it's harder to cut in paste!
Gotta' cut out all those tiny little letters out of the neighbors trashy Playboy
er, Sport Illustrated's!
So when someone WANTS to click on that...
In my browser the link is only "http://www.w3pga.org/Antenna" not the full intended link. Opening it in a new tab doesn't change this.
Yea, you actually have to use scissors and glue...
The DB
Using Google Chrome desktop. Highlight the whole link. Then right click, and then "Go to" the link. Opens right up for me.
it seems that some browsers don't allow url formatting using spaces.
You don't know how to cut and paste that?
Oh Geez...
HTML - Here...
http://www.w3pga.org/Antenna Books/Reflections III.pdf
Keep "%20" it in mind, the Site and or your effort in your browser I'll let you fall flat on your own next time...
I recommend that you go back to your post regarding this and edit the line and re-paste in PLAIN TEXT - then the site, the HTML the browser works in will process the "%20" as a normal space character.
Since you knew by others posting the broken link, just go back and fix it.
Oh Geez...
HTML - Here...
http://www.w3pga.org/Antenna Books/Reflections III.pdf
Keep "%20" it in mind, the Site and or your effort in your browser I'll let you fall flat on your own next time...
I recommend that you go back to your post regarding this and edit the line and re-paste in PLAIN TEXT - then the site, the HTML the browser works in will process the "%20" as a normal space character.
Since you knew by others posting the broken link, just go back and fix it.
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Don't know if this is a coinky dink or not, but immediately after erecting this Sirio 2008 I am receiving skip from directions I was not receiving before. With the old Sigma Silver Rod, I was easily DXing to the south and East. Now, I am also getting strong DX from Canada, Texas, Washington, Cali. etc. Just thought I'd throw this out there.
How is this Antenna working out for you? I'm looking into hearing more from you on it's performance. Thanks
I love this antenna. It talks well and the ears are much better than the old Sigma. My only issue here, is that I can't really get it up as high as I want it. I'm approximately 30' to the base and it's got one tree in front of it. As to the antenna, it's heavy duty and the connectors for the sections are very sturdy. BUT, being the king of overkill, I used heat shrink tube over every joint to help keep the water out. We've also had some nasty winds since it's been up and she's not even slightly bent. Still standing tall. Water and snow do NOT even manipulate the SWR. I call this antenna a keeper.
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