Date
1 - 17 of 17
Antennas: Best Mini-Whip ?? Grounds discusssion
|
Tony_AD0VC
The mini-whip and other e-field probe antennas are, by their nature, high impedance measuring devices. Like the voltmeter on your test bench, they are intended to measure without loading. So, how good of a ground do you think you need? The answer is "not very
good". The coax laying on the ground is often good enough for a mini-whip. A few hundred picofarads is quite large compared to the <1pf the sensing pad. For the mini-whip, I think a good ground has more value for noise suppression than it does for antenna
operation. I always ground a mini-whip at the base of the antenna myself, but I use a 4 foot rod.
For me, the achilles heel of active e-field antennas is overload. I live near an AM BC station and I have not found an active e-field antenna that doesn't have IMD spurs scattered about in the waterfall. I use a passive e-field antenna with an impedance of
50k-100k ohms. A 4 foot rod is still fine for this.
Tony
|
|
|
|
jdow
In general a rod in the ground is a safety ground.
For RF you use radials to get a good ground. And they should be
1/4 wave at the lowest frequency of interest. That will lower the
main lobe on your radiation pattern.
toggle quoted messageShow quoted text
{^_^} On 20210919 08:12:26, Tony_AD0VC wrote:
|
|
|
|
My 4' ground rod (half of an 8' one) at the 9:1 Unun of my 210' long EFW drops the noise floor on 160 and 80M by 1 1/2 S-units, not so noticeable on upper bands.
|
|
|
|
Tony_AD0VC
In general maybe. But in specific, there are hundreds of us LF DXers (world wide) out here who use rods with our e-probe types of antennas. If only we had thought to use radials instead. At least we are safe.
Also, I have not gotten my mini-whip to radiate yet. Maybe thats why.
Irked,
Tony
From: main@SDR-Radio.groups.io <main@SDR-Radio.groups.io> on behalf of jdow <jdow@...>
Sent: Sunday, September 19, 2021 7:48 PM To: main@SDR-Radio.groups.io <main@SDR-Radio.groups.io> Subject: Re: [SDR-Radio] Antennas: Best Mini-Whip ?? Grounds discusssion In general a rod in the ground is a safety ground. For RF you use radials to get a good ground. And they should be 1/4 wave at the lowest frequency of interest. That will lower the main lobe on your radiation pattern. {^_^} On 20210919 08:12:26, Tony_AD0VC wrote:
|
|
|
|
Once my Bovine friends are gone for the winter, I could lay out some radials and compare noise floors of none, ground rod, and radials. Superstation #1 is inside one of the pastures and they will surely get anything I put down on the ground torn up and wrapped around their hooves. Hence I buried, welded together sheets of concrete reinforcing wire around my 160M vertical:
73 Kriss KA1GJU
|
|
|
|
There is no need to make radials 1/4 wave. They have little to do with pattern but a lot to do with efficiency. A wire on or buried in the ground is much longer electrically than it is physically. Some of the best info to be found is on Rudy's site http://rudys.typepad.com/files/chapter-5-.pdf
toggle quoted messageShow quoted text
Wes N7WS
On Sun, Sep 19, 2021 at 06:48 PM, jdow wrote: In general a rod in the ground is a safety ground. For RF you use radials to get a good ground. And they should be 1/4 wave at the lowest frequency of interest. That will lower the main lobe on your radiation pattern.
|
|
|
|
Siegfried Jackstien
hey kriss how long will those iron mats survive in the ground and outside in the weather?!? would it be worth using stainless instead?!? or at least galvanized ones?!? dg9bfc sigi
Am 20.09.2021 um 16:22 schrieb Kriss
Kliegle KA1GJU:
Once my Bovine friends are gone for the winter, I could lay out some radials and compare noise floors of none, ground rod, and radials. Superstation #1 is inside one of the pastures and they will surely get anything I put down on the ground torn up and wrapped around their hooves. Hence I buried, welded together sheets of concrete reinforcing wire around my 160M vertical:
|
|
|
|
Gedas
Yup exactly right Wes. I think
it goes WAY back when ops were making radials for ground plane
antennas where having 1/4-wave radials provided efficiency and
helped provide a good match to 50-ohm coax. Broadcast stations
use even longer radials (usually 1/2-wave) but this is FCC
mandated. Once the wires are on the ground the dielectric
constant kicks in and they become longer electrically. And of
course much better to have a boat load of shorter radials than
a few long ones. Gedas, W8BYA EN70JT Gallery at http://w8bya.com (under repair) Light travels faster than sound.... This is why some people appear bright until you hear them speak. On 9/20/2021 10:51 AM, Wes Stewart via
groups.io wrote:
There is no need to make radials 1/4 wave. They have little to do with pattern but a lot to do with efficiency. A wire on or buried in the ground is much longer electrically than it is physically. Some of the best info to be found is on Rudy's site http://rudys.typepad.com/files/chapter-5-.pdf
|
|
|
|
Gedas
Kriss that will be a fascinating experiment. I hope you are able to do it as it would be very educational and not many people can do. Nothing like empirical data ! Now I know this is probably not going to be possible, and you already know this, but it is not enough to just know that the noise level dropped x dB when using ground system A vs. ground system B. What we really need to know is what happened to the strength of desired signals as well when you noted that drop in noise. It's all about that S/N. Again I know you won't be able
to make those kinds of comparisons, not unless you have
identical receive setups separated some distance apart and
each one using a different grounding scheme.....that is the
only way I could think of to run real-time A/B tests and know
for sure what is going on. Thanks for running the tests that
you have and will be. 73 Gedas, W8BYA EN70JT Gallery at http://w8bya.com (under repair) Light travels faster than sound.... This is why some people appear bright until you hear them speak. On 9/20/2021 10:22 AM, Kriss Kliegle
KA1GJU wrote:
Once my Bovine friends are gone for the winter, I could lay out some radials and compare noise floors of none, ground rod, and radials. Superstation #1 is inside one of the pastures and they will surely get anything I put down on the ground torn up and wrapped around their hooves. Hence I buried, welded together sheets of concrete reinforcing wire around my 160M vertical:
|
|
|
|
Gedas
Sigi the resistance of SS or
steel wires is much poorer than that of copper. Significant
when one is trying to cut every 1/10th of an ohm to maximize
efficiency. Gedas, W8BYA EN70JT Gallery at http://w8bya.com (under repair) Light travels faster than sound.... This is why some people appear bright until you hear them speak. On 9/20/2021 11:59 AM, Siegfried
Jackstien wrote:
|
|
|
|
jdow
That is a lot of rebar if you are running out the
optimal distance of 131' for each radial. It should make a
significant difference. Comments I have seen suggest burying it a
few inches won't make much difference; but, burying it below what
bovines might churn the ground when it gets really muddy might
make it less effective. Your sheet layout may mitigate that. And
hooboy is that gonna be expensive.
toggle quoted messageShow quoted text
{O.O} On 20210920 07:22:07, Kriss Kliegle
KA1GJU wrote:
Once my Bovine friends are gone for the winter, I could lay out some radials and compare noise floors of none, ground rod, and radials. Superstation #1 is inside one of the pastures and they will surely get anything I put down on the ground torn up and wrapped around their hooves. Hence I buried, welded together sheets of concrete reinforcing wire around my 160M vertical:
|
|
|
|
jdow
He hared off in the efficiency direction. Efficiency
is important, to be sure. But you also must look at the pattern.
With a ground rod the radiation pattern's lobe is very much like a
bubble. The antenna spends watts on clouds. For regional
communications that is good. If DX is your goal you want to shape
that into a low to the ground doughnut. The lower the better. Are
there ruminations there regarding power delivered to various
elevation angles or power delivered to the first lobe's peak and
its elevation angle?
toggle quoted messageShow quoted text
Modeling with EZNEC is a good way to get a feel for what transpires with radials, efficiency, and radiation angle. (The paid for version of course. The modeling within the free version is too limited to go a good job.) {^_^} On 20210920 07:51:37, Wes Stewart via
groups.io wrote:
There is no need to make radials 1/4 wave. They have little to do with pattern but a lot to do with efficiency. A wire on or buried in the ground is much longer electrically than it is physically. Some of the best info to be found is on Rudy's site http://rudys.typepad.com/files/chapter-5-.pdf
|
|
|
|
jdow
Ever tried welding stainless? Rumor has it that it's
not easy.
toggle quoted messageShow quoted text
{o.o} On 20210920 08:59:48, Siegfried
Jackstien wrote:
|
|
|
|
Gedas
Piece of cake. Just today I
was brazing a SS U-bolt to a brass collar as I had to make my
own pillow block bearing that will allow my 10 GHz dish to
move up & down in elevation. Welding (as opposed to
brazing) SS is also NP as long as you use the right rods and
current settings. Last week I was soldering SS to SS. Gedas, W8BYA EN70JT Gallery at http://w8bya.com (under repair) Light travels faster than sound.... This is why some people appear bright until you hear them speak. On 9/20/2021 7:32 PM, jdow wrote:
Ever tried welding stainless? Rumor has it that it's not easy.
|
|
|
|
Hello Sigi,
The wire mesh is 3.175mm of regular steel, no paint or other coatings. Will last longer than I will be around on Earth! I have found chicken fence wire underground, much smaller in diameter than what I used, and it’s +50 years old. When I built my barn, I bought the wire… but decided to go with 12mm rebar for more strength. So I welded 4 sheets end to end to make a 5’ x 32’ radial. The Icom AH-4 is for higher bands, 80-10, but on 160m, it’s not needed. Was originally going to place it on the ground, but with tractors, trucks, and cows… it would get snagged or just torn up. So I scraped a few inches of soil, put down the steel, then spread the soil back on top. 73 Kriss KA1GJU
|
|
|
|
It’s not rebar, just wire mesh that’s used in concrete floors, sidewalks, etc. I bought enough to do my 36x48 barn/workshop, but ended up using 1/2 rebar instead. So far, no cracks in my floor! The sheets are 5x8 of 1/8 steel wire, and once welded end to end, the radials are 32’ long by 5’ wide. This is one of three 160m TX antennas on the farm, others are inverted Vees at ~90’ on two separate towers. But this one plays very well wit only 100watts to a friend 616 miles away.
73 Kriss KA1GJU
|
|
|
|
Joe F. KC8RKL
Slightly OT note:
EZNEC (Pro/2 version) will be released to the public domain effective 1/1/2022.
SRI for the wasted bandwidth if posted here previously.
73,
Joe F. KC8RKL
|
|
|