[Lowfer] Frozen trees ??

[jrusgrove at comcast.net]

Rick

The 90' top loaded vertical has been in use here on 137 and 500 kHz for many years. In addition to 
the motorized variometer, a tapped primary and secondary ferrite transformer is used to match the 
antenna R to 50 ohms. It is adjustable in roughly 1.5 - 2 ohm steps . An M0MBU Scopematch monitors 
the voltage and current waveforms in the shack. I can see small changes in resonant frequency as 
well as the resistance match at a glance on the dual trace scope.

There are hardwood trees starting approximately 60-100' away from the vertical in two directions, a 
bit further than that in the other directions and some open space in selected areas. Antenna R 
changes markedly from season to season on both bands. It is not unusual to see close to a 2:1 
resistance change from the 'dead' of summer to the 'dead' of winter. There are three noticeable 
times where the match must be changed. #1 setting, the highest resistance is always mid summer. #2, 
the 'intermediate' setting, resistance drops when the trees lose their leaves. #3 setting, the 
lowest R, is when the wx finally turns real cold - temps dipping into the teens or below. There are 
'transitional' resistance settings in between of course, but it becomes obvious there are three 
'major' set points based on the number of trips to the 'doghouse' to change tap settings.

As mentioned on the reflector a while back, it's my hypothesis that trees, in anticipation of cold 
temps, start pulling the sap out of the smaller branches and limbs and back into the trunk and 
larger leaders. This is when the leaves fall and the antenna R starts to drop transitioning into the 
#2 settings. At this point my hypothesis is that that moisture remains in the trunk and larger limbs 
as they are less apt to freeze than the thin branches that support the leaves. As the weather gets 
colder and colder more of the sap goes into the root system to protect the trunk from freezing. The 
#3 settings are likely a combination of maximum sap 'drain down' as well as the ground becoming 
frozen solid. The #3 settings can go dramatically low given extreme cold weather. Once the ground is 
frozen solid the antenna resistance seems to remain relatively low even with short duration warm ups 
... as long as the ground remains sufficiently frozen. When it's obvious that spring is making a 
comeback and the ground thaws the whole situation reverses.

This is just a hypothesis ... have fun poking holes in it! One thing for sure, I doubt that any of 
this is seen at a typical broadcast setup where there are no trees are in the immediate area of the 
antenna.

Jay W1VD  WD2XNS  WE2XGR/2




----- Original Message ----- 
From: "rick kirby" <smokinggun at verizon.net>
To: <lowfer at mailman.qth.net>
Sent: Sunday, January 06, 2013 9:06 PM
Subject: [Lowfer] Frozen trees ??


> Hi All,
>
> As some of you know, this is my first season using  a vertical antenna at
> PBO. I have terrible soil and many trees at my QTH  so I have used a loop in
> the past . Since I  have such lousy soil, I have opted to use no ground
> rods and currently have 60 radials( roughly 2000' of wire) . My loading coil
> is very low loss and has plenty of inductance to resonate my vertical. II
> still get very low antenna current but I really feel the proximity  of trees
> is the reason. Within a 240 degree radius of the vertical, there are trees
> 25 to 40 feet away.
>
> Now I know with a vertical that has a semi-efficient ground system, most
> people notice decreased antenna current when the ground freezes or is wet .
> My radials have been buried under snow for 2 weeks . The temperatures here
> have been in the teens to mid 20s up until 2 days ago . During that time , I
> noticed an INCREASE  in antenna current and my signal was copied  almost 500
> miles away.The past 2 days the temps have hit 40 degrees and I noticed a
> DECREASE in antenna current. The snow is still there so nothing should have
> changed as far as my radial system goes.
>
> Here is the question. could it be that the trees aren't as conductive ( sap
> frozen maybe?) when the temps are real low and they don't  absorb as much
> current from my antenna ? I know it sounds a little strange but its all I
> can come up with. Everything I have read tells me I should lose current when
> temps are freezing but I don't think my ground is a factor.
>
>
>
> 73 and Thanks
>
> Rick   KA2PBO
>
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