Hi Stefan
Which is the turn count on your variometer ?? I can count about 10 in the internal coil but how many in the outer coil ?
May be a variometer is not needed as I can adjust the lenght of the antenna. Althought loosing lenght (height) is never an advantage
a fixed coil would simplify the test
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 :-)
One of the reasons to avoid using the vertical Ae hardwired to GND via coil is not to become the Franklin lighthing arrestor of the building ! :-(
Fortunately the antenna is like a SteppIR (UltraBeam) and the 11m vertical metal element can be rolled down. So it electrically dissapears
There are higher building towers around here and they DO have a lighthing arrestor system. May be this has helped to keep discharges away
so far. But better not to buy tickets for this lottery ;-)
Will keep you (all) updated
73 de Luis
EA5DOM
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
