[Boatanchors] Ground wire? Ho Ho!
Phil
ko6bb1 at gmail.com
Thu Mar 22 00:49:19 EDT 2012
Hi Brian,
Well, for transmitting on HF (when I do operate HF) the antenna is a
ladderline fed 88 foot dipole (semi-inverted vee) into a 4:1 balun, then
the tuner. Being a balanced (???) antenna the grounding probably
doesn't make a lot of difference. Out of MANY different antennas tried
at this "limited real estate" qth it is by far the most effective on
75-10M.
For receiving it's a different story. On shortwave the antenna is
usually configured as the ladder-line fed dipole, but if I use it for LF
(I primarily chase longwave beacons) it's usually switched over to a
"top loaded Tee" against ground fed into a tunable LF pre-amplifier.
The PRIMARY LF and BCB antenna here is actually a short amplified whip
(12 inches long) up ~ 20 feet above the roof.
Since probably 95 percent or more of my work is receiving, and that
mostly below 530KHz (as well as the BCB as an outdoor antenna is needed
for that too), noise is a huge problem (and also a problem in the SW
bands), so all my grounding work is primarily aimed towards silencing
that, something I've been pretty effective at (QRN is a HUGE problem in
this mobile home park). . .
Like I said, this is the summer of "fixing things". There is also a new
amplified whip going up for LF/BCB, probably next week It should be
here tomorrow. It's a specially designed and built active whip with low
IMD from the BCB as I get IMD QRM from AM broadcast stations in the LF
range. . . I decided that while the new antenna was going up I may as
well fix the ground system too. So far I'm very happy with the
improvement the additional rods have made!
You can see a picture of the "antenna farm" at the below website. It's
changed a little, but this is the general idea. The tall "stick"
(Butternut HF-2V) in the middle is gone, and you can't really see the
amplified whip on the back pole.
http://ko6bb1.multiply.com/photos/album/25/New_wire_antenna_Field-Day_2009_from_Home#photo=6
73 de Phil, KO6BB
http://ko6bb1.multiply.com/ (OTR Blog)
http://www.qsl.net/ko6bb/ (Web Page)
RADIOS:
Grundigs: Satellit 750 (2011), S-350 (2006)& G6 (2011).
Icom: R-75 with Two 250Hz CW Filters.
Kenwood: TS130S Transceiver (circa 1980).
Radio Shack: DX-380 digital portable (circa 1990).
Yaesu: VX8R Quad-Band HT (circa 2010).
Zenith: Royal-7000 Transoceanic (circa 1969).
ACCESSORIES: Homebrewed LF Pre-Amp, MFJ-949E HF Tuner
Homebrewed 6 Hz Filter.
ANTENNAS: 88' Long Ladder-line fed dipole, Apex at 35 feet.
Amplified Mini-Whip up 29 feet for LF/MW
Merced, Central California, 37.3N 120.48W CM97sh
On 3/22/2012 4:05 AM, Brian Clarke wrote:
> Hello Phil,
>
> The major omission in your tale is what you say of your antenna -
> absolutely nothing. So, your discussion of grounding is groundless.
>
> You need to consider the purpose of your 'grounding':
>
> Is it for lightning protection?
> Is it for mains safety?
> Is it part of a tuned antenna system?
>
> The correct solution for each of these is different. What you have
> described is faintly appropriate for mains safety, but not lightning
> or RF purposes.
> For RF purposes, there are several possible grounding systems - none
> of which bears any resemblance to what you have described. A tuned
> antenna system will always give the lowest noise - resonance means
> higher Q, means lower bandwidth, means less noise.
>
> If you use a vertical 1/4-wavelength antenna, then your ground spike
> should be immediately at the base of your vertical. That ground spike
> should then be connected to the underlying Earth by as low resistance
> a method as possible. All resistance in your Earthing system is in
> series with your antenna, but as it cannot radiate, all it does is
> heat up the Earth, thereby reducing the efficiency of your antenna.
> To avoid the variability of resistance to Earth, you could use a
> counterpoise system. In this case, the ground wires should be odd
> multiples of 1/4-wavelengths of the frequencies you want to use, but
> kept above the surface of the Earth, and in particular, not Earthed at
> the end away from your vertical. Then, you will have a safety issue -
> the far ends of the resonant counterpoises will be at high Voltage and
> so will need insulation and some means of keeping vulnerable beings
> away while you PTT.
>
> If you use a G5RV or any form of balanced horizontal dipole, then no
> grounding or Earth spike is needed.
>
> However, if you use an end-fed Zeppelin, then how you feed it
> determines any grounding / Earthing you will need.
>
> With your system of Earthing the far end of your so-called ground
> leads at 1/4-wavelengths, you force an otherwise high impedance point
> to be low impedance, and then your feedpoint becomes a high impedance
> junkyard, and the radiation pattern becomes a can of spilt spaghetti.
> Your antenna coupling unit becomes a water heating centre for your
> coffee.
>
> Alternately, you could always imbibe from the ARRL Antenna Handbook.
> On the other hand, you could read any of the multitude of so-called
> expert books on the subject; the problem with this approach is that a
> great deal of what passes for expert comment is a load of armchair
> musings with little connection to physics or electronics. The ARRL
> Antenna Handbook does not suffer quite so much in this regard.
>
> 73 de Brian, VK2GCE.
>
> On Thursday, March 22, 2012 11:36 AM, Phil said:
>
>
>> Hi All,
>> This is the summer of "fixing needed things up around the shack". One
>> of the things that's needed work for a number of years was the ground
>> system (there is NO room around this mobile home for a large spread of
>> buried radial ground wires). For the past twelve years the ground
>> consisted of one copper clad 8 foot ground rod, one 10 foot galvanized
>> rod (the service entrance ground), and two skinny 4 foot ground rods
>> that are now a pile of rust, all tied together at odd distances (for 1/4
>> wave spacing elimination).
>>
>> This mobile home park is a HIGH NOISE dark hole and the existing ground
>> system DID help reduce noise a great deal, though I had to water them in
>> the summer to lower the noise floor. The 'real ground was probably only
>> the ten foot and eight foot ground rods. I've never had an "RF in the
>> shack problem", even when using end fed or "top loaded Tee" antennas
>> against ground
>>
>> Anyway, today I purchased three more 8 foot copper clad rods and drove
>> them in the ground. Two spaced 30 inches apart right where the ground
>> wire enters the shack (nice short cable to the under-bench ground bus).
>> Another one about a foot from the old 8 foot rod, which is located by
>> the North Push-up antenna pole. The 10 foot service entrance rod is
>> between the two groups of 8 foot rods. Everything spaced out so that
>> the "1/4 wave Isolation rule" doesn't come into play, that is I should
>> have an effective ground for any given frequency 50KHz to 30MHz. ONE 4
>> foot rod will remain in service as it seems to be serviceable, the other
>> one I drove in down to ground level.
>>
>> Now the question. The total run to tie all grounds together is about 18
>> feet. I wanted to purchase some copper tubing and have a friend braze
>> it to all rods in an unbroken length to tie them together. However, the
>> budget is about shot, copper tubing is out of the question for now. I'm
>> presently using odd lengths of 18Ga stranded wire for TEMPORARY use
>> (yeah, I know, not the best for RF circuits).
>>
>> I know that they frequently use aluminum wire for electrical service
>> grounds. Anybody see a problem using it in this application? Perhaps
>> it's not as good as a heavy gauge single strand copper wire for RF, but
>> just might be better than I now have. I could then have one continuous
>> unbroken run for the ground, at least until I can perhaps do the copper
>> tubing and braze job later. . .
>>
>> By the way, the addition of three new ground rods, even with funky
>> wiring interconnects already made a HUGE difference in the noise floor
>> at LF and the BCB!!!
>>
>> --
>> 73 de Phil, KO6BB
>> http://ko6bb1.multiply.com/ (OTR Blog)
>> http://www.qsl.net/ko6bb/ (Web Page)
>>
>> RADIOS:
>> Grundigs: Satellit 750 (2011), S-350 (2006)& G6 (2011).
>> Icom: R-75 with Two 250Hz CW Filters.
>> Kenwood: TS130S Transceiver (circa 1980).
>> Radio Shack: DX-380 digital portable (circa 1990).
>> Yaesu: VX8R Quad-Band HT (circa 2010).
>> Zenith: Royal-7000 Transoceanic (circa 1969).
>>
>> ACCESSORIES: Homebrewed LF Pre-Amp, MFJ-949E HF Tuner
>> Homebrewed 6 Hz Filter.
>>
>> ANTENNAS: 88' Long Ladder-line fed dipole, Apex at 35 feet.
>> Amplified Mini-Whip up 29 feet for LF/MW
>> Merced, Central California, 37.3N 120.48W CM97sh
>>
>> ______________________________________________________________
>> Boatanchors mailing list
>> Home: http://mailman.qth.net/mailman/listinfo/boatanchors
>> Help: http://mailman.qth.net/mmfaq.htm
>> Post: mailto:Boatanchors at mailman.qth.net
>>
>> List Administrator: Duane Fischer, W8DBF
>> ** For Assistance: dfischer at usol.com **
>>
>>
>> This list hosted by: http://www.qsl.net
>> Please help support this email list: http://www.qsl.net/donate.html
>>
>
>
>
More information about the Boatanchors
mailing list