OK Roger, very nice!
If you would go to use a PC instead your ears, you could immediately get some
"gain" of say 30 dB and thus much more distance. I also like and normally
prefer CW instead of ear reception. Normally i say " a PC has not to be a part
of a amateur radio station", very conservative, hi. Even my logbock is hand
drawn since i do not like having a PC running during the QSOs. But on (LF)/VLF
it is the best way to communicate. On 137 kHz it is rather due to the activity
that is more in QRSS than in CW but...
So, if you would try SpecLab or Argo on a PC and use a stable VFO i think it is
no problem to reach those 3kms in say DFCW-600. Than, it is much more easy to
improve your system since you can see how a change of your setup improves the
reception. If you can improve some dB, maybe even 10 dB, you could go to
DFCW-60 and so on. And you can really try a TV transformer! That would really
make sense in some kms at small antennas.
Now, as i saw your QTH i get the idea to ask you if you don't want to buy a
kite ;-) It's just funny to have it in the air, even without antennas mounted
on it. Also your grad children would enjoy it ;-) And you would be one of the
top 3 of your VLF dx list ;-)
I think i will ask Bernd/DF8ZR if he is interested to do some ground electrode
tests with me. He is in 16km distance and if we would try DFCW-600, maybe it is
possible. Also it would be interesting to see the QRN/QRM daily time
dependency... All this is interesting stuff.
Go on with your tests and report us :-)
Best wishes :-)
Stefan/DK7FC
________________________________
Von: [email protected] im Auftrag von Roger Lapthorn
Gesendet: Mo 24.05.2010 18:36
An: [email protected]
Betreff: Re: LF: AW: 8.97kHz - Near field and radiated signals?
Thank you for your fast reply Stefan.
In answer to your questions:
* Currently, my TX electrode spacing is 10m, which is the best I can manage
in my small garden. Both electrodes are as far away from the mains and other
utility services as I can manage.
* I have not tried /P transmit testing yet.
* My nearest ham who will listen/look is 3kms away, but using beaconing I am
able to go out myself and see how far I can reach. This is what I have done so
far, going out into the fields behind my house with electrode pairs or a loop
receiver. Best (by ear reception) DX is 0.35kms, but the system has much scope
for optimisation still.
* The largest single turn loop I could erect in my garden would be about
50-70 sq m (about 15m top and 4m-5m high). The longest antenna length would
also be 15m horizontal with some vertical section(s) too.
* The best DX targets are quite modest: I would like to exceed 1km initially
with the TX power I currently have (around 4W). If I could reach G6ALB in the
next village 3kms away I would be delighted. If I got any further I would be
both amazed and VERY happy!
73s
Roger G3XBM
2010/5/24 Stefan Schäfer <[email protected]>
Hello Roger,
For your ground electrodes, ground electrodes may be the best "antenna" in
some 10...10m. I'm not sure how to calculate field strengths but i just know
about the 1/d^3 dependency, so twice the distance means 8 times the power for
the same signal reception, in the near field. But it is the question what are
the electrodes since there is ever a coupling to the mains earth and all the
metallic stuff in regions where people are living so this dependency might not
be valid in your tests. As mentioned here, you could benefit from these
conductors...
But if you want to reach more distance with an antenna of the same size
(e.g. of your garden)and the same power, you could try such a TV transformer.
Take a wire, as long as possible and as high as possible, and apply some kV on
it by this transformer. It can even be resonated by adjusting the air gap
between the both ferrite parts. That results in a maximum output voltage and
thus "ERP". At least this would be a good alternative to your ground electrode
tests. You could easily compare the reachable distances. Here i would use a E
field antenna for reception in the near field.
How far is your next receiving amateur radio station away? And have you
tried to do such tests outside the village/city, just like Jim does it with his
loop antenna? This could allow you to increase the distance of your reception.
Here, space is not limited and you could try 2x10m, 2x50m, 2x100m and so on and
tell us the difference in the feed point impedance at various frequencies and
your ODX :-) Maybe i will also do some ground electrode tests in summer but i
am still not sure. The complete receiver of Jim is a really good idea to check
the QRM situation at a given QTH. Probably i will also buit his loop design for
such tests... Would be interesing what is the maximum distance for a CW
reception of my transmitted signal (with the kite antenna and 6mW ERP) ;-)
I will also do some near field tests in this week, to compare the
performance of my 2 grabbers. This will be done here:
http://www.google.de/maps?f=q&source=s_q&hl=de&geocode=&q=heiligenberg+heidelberg&sll=47.820666,9.312449&sspn=0.106733,0.219383&g=heiligenberg&ie=UTF8&hq=&hnear=Heiligenberg&ll=49.419391,8.704101&spn=0.001616,0.003428&t=h&z=18
in about 1,8km distance to my grabbers. Power will also be below 100W and the
antenna wire will be mounted on a tower in abt 15m height. I will transmit with
this TV transformer on a 40m wire.
Roger, what size is your garden? What is the maximum wire length that you
can apply and in which height? What is your goal (best DX, a reals QSO with the
next equipped station or just do some funny tests?)
So, wish you fun and success with your experiments!
73, Stefan/DK7FC
PS: What is your locator / QTH?
--
http://g3xbm-qrp.blogspot.com/
http://www.g3xbm.co.uk <http://www.g3xbm.co.uk/>
http://www.youtube.com/user/g3xbm
G3XBM GQRP 1678 ISWL G11088
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