Interesting! So, here you could even check the (positive) influence of all the
conductors that could supply the conduction. Who is the RX stn in 3km distance?
Has he also tried to transmit a signal and you tried to rx it?
73, Stefan
________________________________
Von: [email protected] im Auftrag von Roger Lapthorn
Gesendet: Mo 24.05.2010 22:28
An: [email protected]
Betreff: Re: LF: AW: 8.97kHz - Near field and radiated signals?
Attached is a map showing how far I managed on 1kHz earth mode this evening.
Green is strong RS56 signals and orange is just copied RS33 signals, by ear. TX
power 4W + 20m base electrodes, RX 80cm loop.
73s
Roger G3XBM
On 24 May 2010 20:36, Roger Lapthorn <[email protected]> wrote:
Thanks Horst.
I'll try a Marconi antenna at some point, although my space is limited to
little more than the antenna I used on 500kHz (a top loaded 5m vertical).
This evening I extended the TX electrode spacings by connecting one end to
the copper pipes in the house, almost doubling the effective TX baseline to
about 20m. With this, my "earth mode" signals were much stronger and I was able
to cover further than before in a "by ear" walk-about test around the fields.
Ultimate range tonight was 0.4kms using 4W (probably less as the TDA2003 was
hot and probably turning down the power) and receiving on an 80cm loop. active
HPF, small AF amp and crystal earpiece. Range was limited by 50Hz mains hum
and background sferic noise. I must try this set-up with my HF up-converter and
FT817 this week which has good rejection of 50Hz (and its harmonics) mains hum
and a narrow CW filter.
73s
Roger G3XBM
On 24 May 2010 18:18, Horst Stöcker <[email protected]> wrote:
Hello Roger, Dreamers,
if we define near field as < 2 lambda we are talking about everything
below 60 km.With this distance I woul be extremely lucky.
I also do "walkaround tests" near my garden. But I bet only in the flat
field one can see what is possible with small antenna an without a big loading
coil.
Out from my garden I tried my 10h/20t Marconi as well as a 30m earth
base. The Marconi worked better, but not good enough. A TV transformer (must be
flyback of course) made it much better.
But all the trees and houses are coupling the radiated signal to earth
and also the AATIS-RX is very much influenced by them.
I also assume that the horinontal parts of a wire do the same. So only
a vertical should work.
For operation in city environment smaller antennas at the roof top (old
CB antennas) will possibly work better than the bigger vertical in my garden
between trees and houses at ground level. It might be worth a test.
One of the next tests will be with my gig earth base. I have collected
about 800m of surplus wire. Possibly this is another way to even radiate more
then near field. But I would be very surprised it this was good for any DX.
I bet Stefans kite antenna will at least be the only way to DX
operation. Unfortunately this is just portable and just temporary.
vy73 Horst DO1KHS/DI2AN
________________________________
Von: Roger Lapthorn <[email protected]>
Gesendet: 24.05.2010 18:36:28
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?
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