Hi LF
Weekend was profitable in therms of RF current. I was finally able to kepp between 1.4 to 1.6 Amp of antenna current
after reworking connections to the vertical pipe. The PA has been working every ten minutes on WSPR-2 for more than
48 hours without problems
I confirm that need to detune the antenna to get maximum RF current. The optimal point is found down in the Scmith chart
So seems that it happens were reactance decreases. May be related to the low value of antenna capacity I have (180pf)
?
Thank you Paul for another WSPR spot last night. I will shortly upgrade the power supply to 28V and hopefully increase
RF
current too. Step by step ;-)
73 de Luis
EA5DOM
Hi Marco, LF
The pipe runs inside the building in a narrow space. You are right, it is preserved from rain and there should be no effect
at all
It has been working nice in MF so far, and also first tests in LF were very succesful. Last year I could even make a QRSS
QSO with
9A3KB using the Ropex PA with minor modifications
Many variables here. I will rechek connection to the top section of the pipe, which may be failing. And then dropping
the wire
parallel to the pipe if possible. We have a long weekend ahead which can be ideal for this activities …. at limit ;-)
>> My new 2nd DC receiver for MF is in service since a full day so for some time I'll listen
to MF wspr, see you later on LF
More rain here today and antenna wires are down. But sourprisingly I could not get RF current yesterday even with low
impedance
Time to recheck PA with dummy load. May be I have a failure there too
L
Oscar, LU1DOW had a fantastic night yesterday in MF. Spots from the States and again LA2XPA
May be he can try to send an EbNaut message and check if we can finally receive him in central and south EU
73 de Luis
EA5DOM
De:
[email protected] [mailto:[email protected]]
En nombre de marcocadeddu@tin.it
Enviado el: lunes, 29 de octubre de 2018 17:52
Para: [email protected]
Asunto: R: Re: Antenna resistance (Re: LF: EbNaut Autodecoder 137490 Hz: EA5DOM received)
Hi Luis,
while I wish to thank Jay for the nice papers about ERP evaluation, whish to ask you a bit more info concerning the change of impedance.
I understand that is not easy to access all "common parts" which often became "everybody away from it!" I guess it should be feasible to drop a thin, light wire from the top of the building till ground level for a short time a take some measure to compare with
your actual ground.
In this way you should be able to understand if your water pipe is similar or not to the wire (I'm speaking just to measure with a VNA or your analyzer not to transmit high power which could be an hazard for people touching the momentary dropped wire).
It is nice to read that you have seen the pipe junction bypassed from a strip: pipes have usually flanges to joint the sections ore threated ends, in both cases the use of seals can interrupt the ground continuity: by the way I suppose that for possible estinguish
use, in the reservoir there is sweet water (maybe not drinkable but not sea water!) and therefore the electrical continuity is granted from the steel of the pipe and the ground strips not from water! water with low content of salts is almost an insulator rather
than a conductor!
If you have access to the pipe, you could drop the wire there and measure the dc resistance of the pipe against your wire, in the mean time I suggest to check all those stripes even if I cannot understand why a bad contact on one of the stripe could be rain
sensitive... but I guess it is worth to do ;-)
My new 2nd DC receiver for MF is in service since a full day so for some time I'll listen to MF wspr, see you later on LF
Marco, IK1HSS
----Messaggio originale----
Da: [email protected]
Data: 28-ott-2018 14.15
A: "[email protected]"<[email protected]>
Ogg: Re: Antenna resistance (Re: LF: EbNaut Autodecoder 137490 Hz: EA5DOM received)
Hi Markus, LF
The pipe contains presurized water for the fire extinguish system. Is a "wet colum" system. Pipe segments
are connected with big brass links. Should be a good enought current conductor. Down in the basement it
connects with a pressure pump and a water reservoir tank, linked to the water grid system
Will have to check the ground connections of all this stuff when possible. Not easy
But after all, we are all doing all this "not easy" things because it is not easy to work low bands, right? ;-)
Tested mains ground connection too and it helps a lot, but still depends on rain. Access to the ground line at
the lifts engines room on top building is complicated too, as I have no access there because of a AMHPS
(Anti Mad Ham Protection System) hi, hi
Installing my own ground line may be an option, but using light cable. As I can only support the 80m cable
at the top end, so weight must be low. Finally may be the best way to go
> Something gets wet in the basement and the pipe gets a better connection to ground, or at least to the water grid pipes, which finally run underground
Ah that must be the reason! That drain pipe is obviously not continuous metal but inrterropted by some insulating joints or plastic sections, which are more or less bypassed by a water film or flow when it rains.
Could you try to use another ground connection which is continuous all the way down? E.g. external lightning protection conductors, or even the protective earth in your appartment?
Best 73,
Markus
-----Ursprüngliche Mitteilung-----
Von: VIGILANT Luis Fernández <[email protected]>
An: [email protected] <[email protected]>
Verschickt: Sa, 27. Okt 2018 23:17
Betreff: Re: Antenna resistance (Re: LF: EbNaut Autodecoder 137490 Hz: EA5DOM received)
Hi All, LF
Interesting topic. Also happens in MF but in LF it gets more critical. Must be a nightmare at VLF :(
As Marco explained, our setup is not the usual at ground level in a property plot. And in my case ther ground
is 80m away down from the feed point, coil and capacitive topload.
Measured with the antenna analyzer I can see a drop in the impedance module when all gets wet by rain
It is not only an increase of RF current. Today I measured resistance from the ground side of the feed point
trought the pipe to building basement and then returning via the water grid connecting the other side of the
multimeter to a water pipe in my house:
4 Ohm measured early morning when it started with soft rain. At noon we had stronger rain and in the afternoon
I measured again. It dropped to 2 Ohm. Big difference. Something gets wet in the basement and the pipe gets
a better connection to ground, or at least to the water grid pipes, which finally run underground
The top of the antenna is dismantled during storms, so can't measure impedance with the analyzer right now
but bet it is now well under 30 Ohm and would drain a few amps
Other intringuin detail. When it is dry and impedance rises to >100 Ohm the only way to hardly reach 1A RF
is to detune the antenna. I have to set the resonant peak at 138Khz and then at 137,5 get even higher impedance
and high SWR, but the antenna current rises and so the radiated signal. All this at the cost of more amps
consumed by the PA and higer voltage at antenna feed. Running the antenna at the optimum resonance makes
almost no RF current, even considering that this is the minimum impedance point.
About the LPF, this is really the only part of the Ropex PA still in use. This is a link to the schematic with the LPF
Have not tried without LPF. The analyzer measurements are made directly to antenna. But may be a good idea to
make them with the LPF inserted and see what happens
Hi Paul, Luis, Markus, LF
let me join the topic ;-)
the antenna location of Luis is something else of your Markus and Paul and much similar to mine: roof based antennas with elevated ground (in my case) and vertical ground (the water pipe) for Luis.
Anyway also in my case the serie resistance of my antenna increases with rain (almost doubles).
But.. Luis, probably assumes the lower impedance basing on the higher current.
Luis, what kind of LPF have you adopted?
Now I have a T filter with no shunting cap at the input and impedance increases with rain both with and without LPF, but if I remember correctly, when in the past I had an PI LPF with shunting input and output caps the impedance in my shack was transformed
from the transmission line and LPF giving lower impedance by rain.
Could be an explication?
By the way, just for fate it's raining also here and I made some measurement when dry again will repeat ;-)
Have a funny weekend LF
Marco IK1HSS
----Messaggio originale----
Da: [email protected]
Data: 27-ott-2018 12.34
A: <[email protected]>
Ogg: 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.
