In another thread an outdoor antenna system details about a loading coil and a rain cover were presented. The rain cover (Photo) is made of cellular core PVC which may not be an ideal material for this but it should be satisfactory. A discussion related to coil materials is found at this LINK. The outside of the cover was painted with acrylic latex paint which should form a moisture barrier but if the outside painted surface is wet from rain then signal attenuation is expected and this was observed.
The problem presented when after two days of dry weather following rain the field strength did not return to the previous “dry” value. The inside surface of the cover was not painted and it is a possibility that the PVC absorbed some moisture from the humid air. It is known that regular high density PVC will absorb moisture and such data are available but I found none for the cellular PVC. It would be reasonable to assume that this material will also absorb moisture.
As a solution the PVC cover was replaced with one made from a one gallon ice cream container (Photo) which is made from a plastic which should have low absorption. This container was also chosen because of its large diameter which should keep the surface moisture from rain farther away from the coil. Unlike the situation observed when the first cover installation detuned the coil requiring the removal of 1 turn to lower the inductance this cover had no effect at all on the tuning when it was installed.
Satisfied that this cover would work I applied two coats of acrylic latex paint for aesthetics and this is where “watching the paint dry” came into play. With wet paint the field strength was down 3 dB from the dry condition. As the paint dried the FS slowly rose to the initial reading.
It remains to check the new cover’s recovery after a rain. The first cover drying problem perhaps could have been solved by painting the inside surface but the observation that even when dry the cover changed the tuning indicates some interaction with the loading coil which could be detrimental so the choice was made to switch to the new larger cover.
Neil
Another Valuable Concentration of Information
Along with several ongoing projects, I will be setting up an outdoor antenna including the home-built loading coil.
Thanks to this newest post from Radio8Z this whole added science of properly weatherproofing the coil comes to mind.
Building to professional standards is not a breeze, it takes real dedication.
Unfortunately a lot of the people who want to put a signal on the air want it to be simple.
The art and science of broadcasting has trouble with simple.
Hi Guys!
Neil, this is very impressive. What
a nice installation. I am very interested
to know how your setup reacts to precipitation,
temperature, and sunlight shining on the
set-up. (I found that when my installation
was dried out in the warm sunshine, it worked
the best.) I know taking data isn’t easy when
you are doing a lot of other things, but maybe
you can make note of some general trends. Especially
during the wintertime when things are really
different. And when the set-up is sitting
in the freezing cold, surrounded by snow. Snow –
Neil, I forgot what state you are in. But in my
mind, I believe you are in a section of the country
where there IS snow.
Carl, I am really interested in what your triangular
loading coil looks like, and how you made it. You may
have already described it – but if you did I didn’t see it.
By the way, I am almost caught up with listening to your
Low Power Hours.
Bruce, GNAT 90.9, SLUG 88.3, TICK 1020 AM (I’m starting
to fool around with CC experiments again – nothing new –
just what I had before.)
The Triangular Coil
I know there is a picture of the triangular coil and I thought it was posted, Bruce, but it’s not showing up on the website.
I will dig it out and let you know when it is viewable.
This is a much less serious coil than Neil’s, as mine is only built for indoor use.
Now back to dry paint
Weather Effects
It would be interesting to gather information about how the weather affects the field strength and I plan to do so. Thus far it appears that moisture is a major factor in reducing the field strength and it does not appear that this is due to detuning but rather is due to increased losses in the antenna system. It is also possible that since I am using an outdoor antenna for the receiver that this too is being affected. It is going to take a while to sort through this.
One thing on the list is to try RFB’s suggestion of using dry packs in a closed coil enclosure. This would eliminate moisture on the coil as a cause though it now appears that moisture on the outside of the cover is probably the major factor.
Yes, we get snow here in Central Ohio so this will be another vairable to track later on.
One problem with this type of testing is that as a problem is identified and corrected it changes the setup and possibly invalidates prior observations but this is necessary to separate the effects. This is not as scientific as I would hope but it should still yield some useful conclusions.
Neil
.
Wrapping Head
Wrapping my head around this project, I find it to be as solidly scientific as you can get against the wilderness of nature, which evidently has its own science.
Probably the difference in sciences could be described as between fixed measurements and infinitely variable conditions. Have I said something?
Dry inside vs. wet outside. Tricky.
Can’t submerge the coil below ground level to keep it out of the air, because the soil gets soaked.
How about…
Would it help if the coil were double enclosed. What I mean is, a second enclosure to keep the first one from getting wet?
As I understand it the coil does not need to be exposed to the surrounding air because it doesn’t radiate.
What you would be doing is putting the moisture farther away from the coil.
Mini Vac/Hardline Dehydrator
Build a mini vacuum pump attached to a small box filled with dry pack pellets and pull any moisture from the enclosure to the dry pack pellets, exactly like how the much larger dryer systems work with rigid coax and hardline on towers.
A small fish tank pump will do the job for pulling the moisture from the coil enclosure, and have enough push to throw any moisture collected into the box containing the dry pack pellets.
Add dew sensors inside the coil enclosure along the inner wall and one on the coil’s form to activate the pump if either sensor detects moisture. Run all that into PIC controller and program it to maintain a level of vacuum pull even when there is no moisture detected. Keeps everything nice and dry anytime.
RFB
The Rains Came Down
and the field strength came down by 3 dB. A check of the receiving antenna system by noting the FS from two broadcast stations shows no change between wet and dry so it appears the effect is from water on the transmit antenna system.
More will be known when the sun comes out and the recovery is measured.
There is a possible effect from increasing the diameter of the cover in that the water on the outside surface is farther away from the coil which should decrease the effect but the surface area is larger which should increase the effect. Still need to separate this and possible moisture on the coil by condensation.
Neil
Foliage Attenuating Field Strength?
Overnight we had another inch of rain and the received field strength was again down. After some drying today I checked the antenna tuning and it was right on with expected power delivered to the feedpoint.
To rule out moisture in the antenna system the cover was removed and the coil and connectors were heated with a hot air gun and there was no change in the tuning, power into the antenna, nor field strength. This tends to eliminate the water on the cover or coil as the cause of the decreased FS.
The antenna is sited among bushes and these bushes have recovered moisture with increased turgor compared to the previous several weeks of dry conditions. As a test I pulled the bushes away from the antenna and the FS increased with no change in tuning or power in.. For now it appears that the bushes are partially absorbing the signal but are not affecting the antenna tuning or radiated power.
Another test will be in mid November when the leaves fall. I’ll try to remember to post the results here.
Neil
Shadow of the Foliage
A good expression was used in a HAM article I read, and that was mention of “human shadowing” on indoor antennas. The engineering community probably uses this term all the time, but I only first heard it.
With foliage I suspect there is “foliage shadowing”, perhaps most prevalent precisely due to its moisture content as mentioned, and moreso when fresh dew or raindrops are clinging to the outer surface of the leafs or leaves.
During gusty conditions you might see variances in system performance as you would if a person danced around in front of an antenna.
Previous Observations
“Another test will be in mid November when the leaves fall. I’ll try to remember to post the results here.”
Look forward to that. But I can tell you already, based on the photos of the setup, that you will indeed see a change in the amount of influence that surrounding foliage will have when the leaves drop. Now when snow, if you get it and enough of it will build up on the leafless foliage and may present you with an array of refractive elements (snow covered shrub stems) and scatter the field resulting in the increased changes from measurements taken earlier in the year.
The location of the antenna, though not an optimum location, is an excellent location to test a system against such variables like surrounding bushes, trees etc, and through the seasons.
I like real world testing. And this right here is the real deal.
Side note: A comment made earlier about virtual hitting the mark with real world. BZZZZZZZZ!!! Nope. Even that virtual world simulated result relied on a set of “common” values input which is close, but not exact to what would be found at Neil’s location. Even those charts are off a bit so at best one SHOULD have said “here is where the simulated virtual world can come CLOSE to actual world results” rather than what was said.
Now enter actual world measured values into that sim and you WILL get a different result, even if that result is a percentage, because at flea power levels and limited antennas and everything else that seriously affects a 219 outdoor system, that little percentage means a lot.
RFB
Wind, Foliage, and Other Things
Carl posted “During gusty conditions you might see variances in system performance as you would if a person danced around in front of an antenna.”
Indeed, I have observed a fluttering of the FS with the wind blowing. Not surprising given the location.
RFB,
We do get snow (up to about 18 inches on a bad day) which would bury the coil assembly and which will probably detune things to the point of not being useful. We also get ice storms which in addition to snow on the branches may yield some data.
Here’s what is known now.
The phase angle with and without the small PVC pipe cover in dry conditions changes by -26 degrees indicating that the PVC material (or paint) changes the tuning. When tuned to near 0 degrees angle (+/- 5 degrees accepted) for both conditions the field strength and antenna V and I are the same with or without this cover so the main effect of the cover is detuning rather than absorption. This is easily compensated by tuning the coil with the cover in place.
The phase angle with and without the large cover (painted ice cream bucket, 7″ diameter HDPE) does not change so this cover has no observable effect on the tuning likely due to the larger diameter and/or the different material.
The drop in field strength after rain is the same for both the large and small cover and is about 3 dB. The phase angle did not change from before to after the rain using the large cover which suggests the lower FS is due to signal absorption rather than detuning. I do not have reliable phase angle measurements dry and wet with the small cover. Though the observed FS from two broadcast stations didn’t change wet vs. dry I don’t have complete confidence in these because the FS indication changes with modulation. There is not enough dead air to get stable readings. A check of FS using the indoor transmitter and tx. antenna showed no change wet to dry for the outdoor receive antenna but it could be that the receive antenna feed line, which runs near the indoor tx. antenna was picking up signal and this could have swamped the outdoor signal.
The latest data for the antenna system taken four days after 1″ of rain (large cover with the soil moist) shows that the FS is the same as it was before the rain. The four day after rain data are:
(small PVC cover)
V(feed point) = 1.88 V
I(feed point) = 44.5 mA <0
Calculated feed point resistance = 42 ohms
Calculated feed point input power = 84 mW.
(large HDPE cover)
V(feed point) = 1.85 V
I(feed point) = 43.6 mA <-5 Calculated feed point resistance = 43 ohms. Calculated feed point input power = 81 mW (neglecting the phase angle) (Note that the coil was tuned to be close to 0 degrees for each of these measurements.) The transmitter input power cannot be accurately measured with this arrangement since being close to the antenna changes the input power. The power measured using a 48 ohm dummy load (closest value available to 43 ohms) was 96 mW. The antenna measurements were made using coax cables to connect to the tx. and antenna and measurements were made 20 feet from the antenna so as to reduce proximity effects. The use of the cables may influence the data somewhat but there is little change in FS with and without the cables attached giving some assurance that this effect is minimal. The slight differences between the measurements for the PVC and HDPE covers may be due to their effects but they also may be within the margin of measurement uncertainty. I doubt I will be outside at the site during snow and ice and cold rain repeating these measurements but I can easily monitor the field strength. I am planning an indoor receive antenna to eliminate any possible effects caused by weather to the outdoor receiver antenna. This began as a simple test to measure the antenna parameters and to tune the coil but, as is not uncommon with such projects, more questions are raised than answered after the observations are made. Sometimes pursuing observations which don't fit the model leads to discovery. I am trying to determine which are important and which are not and suggestions will be appreciated. Neil
Zeniths and Azimuths
Coils are utilized to spin an electric signal in a circle, as many times as it takes.
Other wiring arrangements send signals in very straight directions, as with a dipole antenna.
The directionality and orientation of signals, coming and going, is a science unto itself.
Has the field of azimuth and zenith, with regard to electric signals, been fully explored?
After all, we are in a round world, where the flatness of the ground is only a local illusion..
We are entering the realm of confusion, where this way may not be true left, nor that way absolutely up.
Just for grins let’s ask, if the earth were removed from the equation, how would we do it?
What does air do to FM signals?
When a glass of water is taken from the tap, does the entire electro-magnetic spectrum shift?
When a dog ….
By now I had hoped to make a point. But then, why is “making a point” always the point? What about the vast territory between points? Places that have no point. Let me look up “point”, this is getting good.
Philosophy
Carl,
My answer to your question “Has the field of azimuth and zenith, with regard to electric signals, been fully explored?” is no. Do we know enough to make reliable predictions? The answer is yes. Could there be very small unseen errors in such predictions? Yes. Are there? We don’t know but quantum theory predicts yes. Is this due to a flaw in our theory or is it a property of nature? It may be a flaw but it is known to be a property of nature (Heisenberg’s uncertainty principle). And so on and so on and……
Throughout my posts in this thread I have tried to explain my observations based on known cause and effect which is itself based on theoretical and empirical information. For example I try to explain the observed decrease in FS with rain in terms of known effects, namely energy dissipation in water and detuning of the coil by capacitive effects. These two are known from both theory and observation. I believe I have separated them to where I can claim that the decrease is due to energy dissipation.
Is this the truth? Probably, but it is possible that Martian invaders are here stealing the energy when it rains. It becomes a matter of probabilities. The dissipation explanation is much more probable to be true than the Martian one but this doesn’t disprove the latter.
An observed effect could also be the result of some yet unknown cause. Sometimes observations which do not conform to known science lead to the realization that the science is either incomplete or is flawed. An example of this is how quantum theories unraveled the postulates of Newton and Laplace on the deterministic universe. Even today, just when it is thought that all particles have been discovered, more are needed and are usually found to make the theories explain the observations.
There are many books on this subject and one which I have just finished reading is “The Matter Myth” by Davies and Gribbin. Another good one to start with, if interested in such things, is “In Search of Schrodinger’s Cat” by John Gribbin.
We know a lot about physics and how things work but we do not know everything, yet what we do know is very useful.
Disbelief
In my disbelief I think that music passed through the air would have occasional sightings of tubas or bass viols coming in and out of view as they flew through the air at light speed.
I have yet to see a drum in the sky.
Yet I hear drums on the radio.
Oddly, the radio stands in perfect sight.
Dwelling On The Same Thing
More dwelling on how electric signals obey certain rules based on whether they are traveling in a straight line or spinning in a circle. Very fascinating.
True or almost false: ground radials work best when laid straight, without bending.
False or slightly true: antennas work best if they don’t have a curve in their shape.
Inquiring minds never stop asking.
Update on Field Strength After Rain
There are new data on the decrease in field strength which was suspected to be due to moisture on the foliage which shows this was not the case. Using an indoor antenna for the field strength measurement shows no decrease in field strength after rain at the same time the outdoor receive antenna shows a 3 dB drop after rain. The loss of signal is in the outdoor receive antenna.
The receive antenna was erected 24 years ago and the feedline had been replaced and checked but the last 25 feet of line is the original coax. The coax has become brittle and shows signs of moisture invasion (green color on shield and insulation) and this is most likely the cause of the loss observed. It was noted that the field strength using this antenna did not return to the “dry” value for several days after rain even though the moisture had evaporated which was probably due to the moisture trapped inside the coax taking a long time to evaporate.
This is good news in that the transmitter FS is normal after rain but it remains to track this during rain. The bad news is that some tree climbing with new coax is in my future.
Neil