Jim
When you say it measured 70K was that DC, low frequency (60hz) A/C or at
1.8/3.5 Mhz RF?
Big difference.
'
Here two 5' rods about 2' apart measure about 2K DC but measure about
600 ohms at 1.8 Mhz...Still not sure how that correlates to a larger
earth RF ground. The other thing is RF ground varies not only with the
soil type but frequency
Dave
NR1DX
On 10/18/2019 10:51 AM, MU 4CX250B wrote:
Thanks for the suggestion, Dave. I’m using DXE hardware and relay
boxes for switching, and twin lengths of WD-1A mil surplus telephone
cable for the wires. The lengths are spaced roughly 6 inches apart to
approximate 450 ohms. The end terminations are three 8ft ground rods
spaced out about 4 ft apart (12 ft total).The soil is soft, silty, and
relatively alkaline, but not as sandy as yours seems to be.
I did try to measure the ground resistance once. My 160/80m
transmitting vertical (70 ft self-supporting aluminum mast,
base-loaded with a switchable vacuum relay) is about 800 ft from my
shack and fed with hardline. The end-to-end resistance of the hardline
shield is only an ohm or two. The vertical has sixty 120ft radials
strewn out across the soil, and an 8 ft ground rod at the base. In my
test, I disconnected the hardline from the vertical, but left it
connected at station end, where it was well-grounded. I measured the
resistance between the ground rod at the base of the antenna and the
disconnected hardline shield, and it was about 70K ohms. With 800 ft
separation, the soil resistance approximates a two-dimensional
conductor and is independent of the spacing between the measurement
points. Thus the 70K resistance is an approximation of the actual soil
resistivity. I wish I could compare that value with measurements on
other soil types.
73,
Jim w8zr
Sent from my iPhone
On Oct 18, 2019, at 7:53 AM, Artek Manuals <Manuals@artekmanuals.com> wrote:
Jim
Poor front to back can indeed be a result of being too long. Although w8JI
would argue that at 700 feet your just about at optimum (1.5 wavelengths) I
would think it would be easy to add an insulator /jumper and a set of
terminations and grounds at ~500 feet and see what the difference is.
What kind of grounds do you have at the ends? Living on a granular quartz plane
myself with very poor ground conductivity ( I can push a 5ft length of 1/2"
copper pipe 3ft in the ground by hand (pure sand!) and easily tap it in the last
two feet with a hammer) I would think that the grounds at the end would indeed have
an effect on front to back or RDF which is the latest popular figure of merit ( how
do you actually MESAURE RDF?).
I often wonder how one knows when one has a "good enough ground". I have read
https://www.w8ji.com/beverages.htm many times. Tom suggest a proxy method using temporary
radials which I don't have the topography to install in a meaningful way. The net result
is I take Tom's measurements with a grain of salt since they are done on soil with much
better conductivity than you (apparently ) or I have
Dave
NR1DX
On 10/18/2019 8:51 AM, MU 4CX250B wrote:
On this general subject, I’m using bi-diectional beverages 720 ft
long, suspended 7 ft above sandy desert ground. The F/B ratio is poor
(not important for New Mexico) but I’m wondering if the antennas are
too long? I use them on 80m/160m.
73,
Jim w8zr
Sent from my iPhone
On Oct 17, 2019, at 9:31 PM, Artek Manuals <Manuals@artekmanuals.com> wrote:
Tim
Which antenna will you be using ; BOG, Beverage or a FLAG/Pennant
I have been doing some experimenting with the BF-4X with BOGs and Beverages in both very poor sandy
soil and then again at a water front (salt) canal location. Eventually I will get around to trying
out a FLAG/Pennant style as well. Seems to work pretty well in my dry sandy location� the
performance has been less than stellar so far next to the saltwater canal, I think this may have
more to do with the seawall near by. This is a BOG issue and not any problem with the BF-4X boxes.
with BOGS i tried it in an end fed and center� fed configuration� and an of center
feed with a beverage.
The for BF-4X literature says BOGs from 100 to 300' . For my poor soil conditions
I find that 200' ( as many other s have reported for BOGs) is the upper limit>
performance was noticeably poorer at 225', 250' and 350' . This is a function of
soil conditions and not the boxes and YMMV.
Dave
NR1Dx
On 10/16/2019 11:35 AM, Tim Duffy wrote:
Thinking about the Fall Stew coming up this Saturday, I will be trying out
the BevFlex-4X that W9XT is now manufacturing.
Here is the flyer:
<https://static.dxengineering.com/global/images/technicalarticles/ums-bevfle
x-4x.pdf>
https://static.dxengineering.com/global/images/technicalarticles/ums-bevflex
-4x.pdf
And the BevFlex-4X details:
<https://www.dxengineering.com/parts/ums-bevflex-4x>
https://www.dxengineering.com/parts/ums-bevflex-4x
73
Tim K3LR
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