Hi Luis,
Am 19.05.2015 19:03, schrieb VIGILANT Luis Fernández:
I have been using the vertical antenna (11m really) as a first Tx Ae, with NO loading coil
No coil? That is the reason! With a correctly resonated and matched
antenna you will easily 'gain' 40 dB!
55 pF on MF is about -j 6.1 kOhm. If you run a PA which applies a
constant voltage to the antenna, the current is 50/6100 times lower
than at 50 Ohm (not the same TX power of course. It is just an
assumption to calculate something). Then the ERP is about 42 dB
lower!
It is quite easy to wind a coil for MF. For that antenna i would
recommend a 20 cm diameter tube and simple 1.5mm^2 electrical wire.
I used a similar motor driven variometer
https://dl.dropboxusercontent.com/u/19882028/MF/MF%20motor%20variometer%20coil.JPG
on MF, until there was a HV breaktrough at 1.000 W ERP:
https://dl.dropboxusercontent.com/u/19882028/MF/20141027_203720.jpg
and 11m wire hanging down as counter poise.
There is really now metallic structure on the top of such a building? I
cannot imagine. There must have been lightnig strikes from time to
time. If not, the next strike will show you where the next earth
connection can be found :-)
The building structure is made of metal reinforced concrete. Probably the choice to get a counter poise
is the fire extinguish wet column, which runs inside the building. A true metal pipe filled with water and not connected
to houses, just to hoses for emergency use.
Sounds very useful! I would use that.
I can also run a wire down parallel to this pipe but not sure
if can connect it to true ground at the bottom
Which feeding system and coil do you suggest ?
I suggest something like shown in this schematic: A 50 Ohm cable, a
galvanically decoupling transformer which is matching the residual
losses(+ the small radiation resistance) to 50 Ohm and a variometer:
https://dl.dropboxusercontent.com/u/19882028/LF/schematics/LF%20H%20bridge%20PA%2C%20DK7FC.png
Perfectly understood the path stability problems on MF Stefan. At the moment I keep QRSS on 476.177
and got reports from EA1FAQ, EA4NZ and EB3FRN. I have set a kinf of "contest" sending different messages
that they have to copy. This are some winner screenshots. Tx time for DFCW is 60 sec. Will try shorter
https://dl.dropboxusercontent.com/u/7162072/Docs/EA1FAQ%20Rx%20QRSS%20MF%2015%20mayo%202015.jpg
https://dl.dropboxusercontent.com/u/7162072/Docs/EB3FRN%20copy%20EA5DOM%20QRSS%20476KHz.bmp
https://dl.dropboxusercontent.com/u/7162072/Docs/EA4NZ%20Rx%20QRSS%20MF.jpg
LF/MF
Always learning ! Always fun :-)
73 de Luis
EA5DOM
Very nice! Keep the band alive down there in EA. (Uuuh, reminds me that
i've not really been active in the recent time, at least not in CW).
I'm looking forward to your progress!
73, Stefan
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