Hi Stefan
Thanks for the reply. Sorry to hear that my ERP will be so
little with this setup. A few 10dBs is a lot, I had no idea it would
be that much. I just assumed I could make up the difference by running
a much larger audio amplifier. It would no be hard to put 1KW
amplifier on with the availability of some cheap 12V car amps now
available. But maybe this might not be enough power.
For MF I'm currently using a inverted L ~73m long, 24m of that
has 3 wires as a top hat, but hopefully will be increasing that soon.
The height of the antenna is ~24m at one end and >36m at the
farthest end. The Tx is a HB set up with 4 FETs running class D,
capable of 1KW but I have not pushed it that far as yet. I have been
limiting it to ~300W for local contacts between here and stations South
of the Island. I use an Icom R75 receiver for receiving, it seems to
work very well on MF. Best heard DX so far on WSPR is ZL2BCG and VK4YB.
I was hoping you would say that QRSS240 would work with this
limited budget set up. It doesn't sound like I need to proceed much
further unless I can find a much larger audio power amplifier, a lot of
patience, a lot of luck and a good GPS receiver. I did look at a few
of the
NEO-6M GPS units, but not sure which one on Amazon
you were referring to.
I agree maybe I could go on the reflector with our
conversations, however since using even moderate size loop on this
dreamer's band does not look realistic, perhaps it would be a waste of
everyone's time?
I'll play with it for a few more days if things don't improve
I'll pack it all up.
Thanks for your help Stefan.
73, Jack - VA7JX
Hi Jack,
Can we do the conversation on the reflector maybe? There is little
activity and each conversation may help to rise some inspiration to
lead to an increased activity... Your decision, just reply to the
reflector in the next answer if you like.
Well, i understood the procedure you're describing and this is of
course the way to go for getting a resonance on the desired frequency.
But, the ERP will be so little with this setup, i guess you are a few
10 dB away from leaving a trace on VE7SLs site.
Which antenna are you using for LF and MF? A typical top loaded
vertical antenna will give you the best results on VLF as well. What is
the capacity of that antenna, in pF?
But i understand, a loop is much easier to match on that frequency,
easier than winding a large coil :-) But if you want to cross 186 km,
which is a serious distance already, you will need to large coil and
several kV across the antenna!
Furthermore you won't manage QRSS240 on that band. QRSS 240000 is more
realistic! That means, you need a receiver and transmitter that has the
necessary stability. The cheapest and best way to go is using a GPS
module like NEO-6M, which is available from Amazon. It provides a PPS
pulse which must be fed into the mic input of the soundcard. Together
with SpecLab you can generate a perfectly stable tone then, as well as
DFCW, QRSS, EbNaut, etc.... The same must be used on the RX site.
It is also helpful to do local tests, maybe with a notebook, in
1...2...3...4...5...6 km distance, just to get an impression...
What do you think?
I would say you can build the system from junk box parts mostly, that
the advantace to the activity on the other end of the spectrum :-)
73, Stefan
Am 04.09.2017 22:42, schrieb JACK ASKEW:
Hi Stefan
I'm having problems finding your right email, so if you get
this
twice I apologize.
I have been trying to get a signal on 8.970kHz but with little
success. Since I'm on a limited budget, I have decide to try a large
coaxial loop instead of a large coil. I chose RG-59 coax (center and
shield) since it has a low resistance as appose to copper wire. The
bottom of the loop is only ~10m off the ground but the top side is ~21m
up, circumference is ~76m. The mid point goes down to a matching box
consisting of a pc board with HV caps and a FT-240-78 core with a sec
and pri winding. The primary is 11T of of #14 ins wire and a secondary
of #18 awg enamel wire with 55T which connects to a chassis mount SO239
for the coax which goes back to the Tx amp ~30m away. The HV caps
totaled 2.86uF and is in series with one side of the coax loop. The
loop measured 100uH, so the combined capacitors plus the 100uH loop
seemed to be close to the calculated values, but I think it could have
been higher. The Tx is a simple 140W audio amp driven by a Windows free
downloaded program called Audio Measuring Systems. I measured 2A of RF
using a calibrated RF ammeter. The same meter was used to select the
capacitor values for maximum O/P. I tried using a scopematch designed
for .475 MHz but I guess the toroid across the internal coax line is
too lossy as it gets warm and besides the current reading was very low
compared to the voltage.
I don't know how far I can Tx yet. Steve, VE7SL has tried to
receive me, he is ~186 km and used a Perseus receiver with ~24Hz BW and
QRSS 240 but no luck so far.
We think we might have too low of a EIRP for that distance.
Is there any other way of optimizing the RF O/P besides using
a
RF ammeter?
Your thoughts on this would be much appreciated.
Thanks in advance.
73,
Jack Askew - VA7JX
