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Re: Antenna resistance (Re: LF: EbNaut Autodecoder 137490 Hz: EA5DOM rec

To: "[email protected]" <[email protected]>
Subject: Re: Antenna resistance (Re: LF: EbNaut Autodecoder 137490 Hz: EA5DOM received)
From: Laurence KL7 L <[email protected]>
Date: Sat, 27 Oct 2018 14:58:36 +0000
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Thread-topic: Antenna resistance (Re: LF: EbNaut Autodecoder 137490 Hz: EA5DOM received)
I would absolutely agree with Jay - and your comments Paul - proportional and 
differential - the trees react very fast to external temps and clearly seen on 
losses - The White Birch especially, my Conifers not so much

ive reduced the variability but earthmatting to close to 100ft radius and then 
tying all the extending radials out to 200ft with a perimeter ring wire - this 
seems to have stabilized wx variables a lot - that and a chainsaw

Laurence KL7L

> On Oct 27, 2018, at 3:47 AM, "[email protected]" <[email protected]> 
> wrote:
> Paul
>> I am no expert but I guess the trees are partly responsible for the
>> high resistance and the drop with freezing temperature?
> It's been my 'hypothesis' that as the temperature cools the sap heads toward 
> the roots in stages ... not in one big rush. As the temperature heads toward 
> freezing, sap first leaves the small branches and small leaders heading for 
> thicker parts of the tree. As the temperature further decreases below 
> freezing the sap heads to the trunk ... and finally to the roots when it gets 
> really cold. In short, it would seem the trees have a proportional response 
> to the cold temperatures. At least this would explain antenna resistance 
> observations at this location with changing temperatures. 
> Some good info on measuring field strength at: 
> John and I both used identical setups and they worked exceptionally well.
> Jay W1VD  WD2XNS  WE2XGR/2
> ----- Original Message -----
> From: N1BUG <[email protected]>
> Reply-To: <[email protected]>
> To: <[email protected]>
> Sent: 10/27/2018 6:34:57 AM
> Subject: Antenna resistance (Re: LF: EbNaut Autodecoder 137490 Hz: EA5DOM 
> received)
> ________________________________________________________________________________
> Hi Luis, Markus, LF
> This is a very interesting topic for me too.
> My antenna resistance is very high, usually more than 100 ohms. I
> think there may be a few reasons. There are trees near the antenna
> which I presume to be lossy. My antenna ground system is not tied
> into the house ground, in order to minimize 120 Hz sidebands on my
> transmitted signal. When I tie the grounds together the level of
> these sidebands increases almost 20 dB. Also my RX antenna is more
> noisy when the TX antenna ground and house ground are tied together.
> I suppose this is because more noise is radiated from the TX
> antenna, then picked up by the RX antenna which has its own small,
> isolated ground.
> Rain has no effect on the antenna resistance, but temperature does.
> During summer there is little change, just minor variations. But as
> the temperature drops and begins to approach freezing, resistance
> begins to get lower. There is a big drop right around freezing or
> few degrees below, but resistance continues to drop with even lower
> temperatures, reaching minimum on the coldest winter nights. Last
> winter I saw it reach 40 ohms a few times. :)
> I am no expert but I guess the trees are partly responsible for the
> high resistance and the drop with freezing temperature?
> Anyway I can run enough power to reach calculated 1W EIRP and it's
> enough to be heard across that little pond. :)
> But here is a related question: I have calculated my EIRP to be one
> watt using the measured resistance, antenna parameters and current.
> But does this calculation include all the losses in trees? If I had
> the proper equipment to make field strength measurements at a
> distance, would I find that my EIRP is less than one watt due to the
> tree losses?
> 73,
> Paul N1BUG
>> On 10/27/18 5:45 AM, Markus Vester wrote:
>> Hi Luis,
>>> Impedance drops a lot after rain
>> This seems unusual. I have exactly the opposite effect here:
>> Series resistance at 137 kHz is normally around 20 ohms
>> (including 5 ohms for the coil). When it rains it get worse up to
>> about 40 ohms, whereas best times are cold and dry winter days
>> with ~15 ohms when the trees are solidly frozen. So I presume
>> that the major contribution to my resistance are
>> capacitively-coupled losses in vegetation and other nearfield
>> environment. The ground connection itself (the "house earth"
>> which is connected to electric grid PE, and also pipe systems for
>> water supply and distict heating) seems to have a low resistance.
>> My only explanation for lower wet resistance would be if one were
>> using a separate radial system in the garden, whose connection to
>> ground might be better when the lawn is soaked. But I don't think
>> this applies to your setup at all.
>> Best 73, Markus
>> Von: VIGILANT Luis Fernández
>> I'm struggling
>> here with the antenna. Most of the time impedance rises and I
>> hardly run 1A RF current
>> Rainy weekend here.
>> Impedance drops a lot after rain. Let's see how much current can
>> drainLast time I could see almost 4A RF.

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