Hi Steve;
Even though I am about 80km from the nearest MW transmitter, BCB IM is a
constant issue here. Considerably worse in the winter. I am always VERY
suspicious that any crankup towers would be a significant contributor to
the creation of IMD products, both because of the sliding sections and the
cables. Many of the conventional bolt together towers here, have bonding
straps across the tower section splices. A few years ago I ran a length of
1/4 aircraft cable up along the tower, over a pulley (metal) and out to
form a catenary line. Instant intermod everywhere. Unless the crankups use
insulated pullies...
Don
VE6JY
On Wed, Dec 7, 2016 at 9:43 PM, Tim Shoppa <tshoppa@gmail.com> wrote:
> Steve - when I see an increase in Intermod, my mind goes away from poor
> grounds, and towards oxidized connectors and flaky relay contacts.
>
> Reseat all connectors, tighten all screws, and hot-switch relay contacts
> till you find the offender.
>
> Tim N3QE
>
> Sent from my iPhone
>
> > On Dec 7, 2016, at 4:35 PM, VE6WZ Steve <ve6wz@shaw.ca> wrote:
> >
> > I’m wondering what experiences are out there regarding small vertical
> array, or beverage performance in the winter over frozen ground.
> >
> > The reason for this question is that over the last 2 weeks or so, my
> HI-z (24’ vertical) SDR skimmer antenna at my remote QTH has shown somewhat
> diminished performance and a dramatic increase in AM inter-mod byproducts
> on 160.
> > During the somewhat hasty install of this antenna (the SDR “RBN skimmer”
> antenna was not considered an important part of the station) I had some
> trouble driving the ground rod for the HI-z amplifier and only ended up
> with about 3’ of copper pipe driven into the ground. During this past
> summer and fall the performance was good.
> > Winter has been here for a while. Last night it was -28 deg C. Today,
> that rod is now probably sitting in a block of solid ice. (ok, not solid
> ice, but the conductive dissociated ions from the native salts distributed
> within the soil are now locked in ice)
> >
> > In truth I am not really concerned about this particular antenna, but I
> do plan to install an 8 circle array as well as some beverages this summer
> and this problem got me thinking about making sure I have a “seasonally
> stable” ground system up here in the frozen north.
> > Some quick research points to potential frost depths ranging from 6’-8’
> depending on snow cover and soil type. Perhaps driving deeper rods could
> help, but it seems to me that there will still be a seasonal change of
> consequence. Literature associated with various short vertical array
> products indicate that 3’-4’ rods should be adequate, but is this true in a
> northern climate?
> > For the most part, I could care less whether the array works in the
> summer…..it’s during our winter DX season that I want performance.
> >
> > Perhaps a very carefully designed and symmetrical short ground radial
> system could stabilize things, but I know with phased rx vertical arrays
> this can be a big problem and cause phase imbalances. Perhaps on my
> beverages a small radial system at the termination would be helpful.
> >
> > I am not new to rx antennas, having built and used numerous single wire
> beverages, reversible beverages and end-fire phased beverages as well as
> passive and active (Hi-z) phased vertical arrays at my home QTH, but have
> never “noticed” a problem.
> > BTW, it is possible that there is something else going on with my SDR
> antenna other than a ground problem, and I will be checking that out next
> time I’m at the station. However, I think I’ll still want to consider the
> frozen ground impact even if there is something else going on.
> >
> > Any experiences, measurements or ideas from those living in places where
> it snows a lot, you have something called a “block heater” for your car,
> and when you work outside you last about 5 minutes before your hands and
> toes are numb??
> >
> > de steve ve6wz.
> >
> >
> > Steve Babcock
> > Lead Geologist, Mature
> > TAQA North Ltd.
> > D +1.403.724.5147
> > M +1.403.870.0082
> > 2100, 308 – 4 Avenue SW, Calgary Alberta
> > Canada T2P 0H7
> >
> >
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