On Tue, 14 Dec 2010 09:17:40 -0800, Wimpie wrote:

Regarding tuning, loops and (long) wires.

You probably locate your antenna far away from noise sources. Mostly
this is not where your receiver is.

That's a problem, indeed.

In case of tuned loops, you have to go outside for each significant
frequency change. This is one of the reasons that I want my
preselection / tuning adjacent to the receiver.

It seems there is another solution. The varactor diodes seem to act as a
variable capacitor driven by their voltage (the capacitance of this kind
of diode decreases as the potential is increased).

It seems there are some loop designs with varactor diodes as tuners.

But I don't know what could be the price of a such solution.

Loops aren't magic things. A wire from your balcony to a tree or other
tie point may give better S/N ratio then the best (expensive) loop on
your balcony.

I think so, but there is nothing I can change for that today.

Best matching isn't required for reception at HF, just sufficient
signal. In case of a PI tuning / preselector device, you need to adjust
two capacitors in case of major frequency change. In my opinion a
single capacitor device is more pleasant to use.

I will try different configurations when I get them.

If you want to experiment with some long wire (unbalanced) antennas,
make sure to have a ground (counterpoise) provision outside; otherwise
your coaxial cable will be part of the antenna. This may result in more
interference from indoor sources.

Yes, but the place I plan to experiment should be far away from this kind
of trouble... I won't be able to get a good ground there.

If you use a tapped coil preselector (like the one in my link),

Sorry, where is it in your web site?

and have
sufficient noise from the antenna, you may even change the taps. The
preselector will give more insertion loss, but it will be more selective
also.

How is called this design?

This can be of use when you have strong signals in your
neighborhood. Because of portability, I frequently use an AOR AR8200.
Without preselection, such a wide band receiver is useless with an
external antenna.

I don't like these receivers... Or they should be used with
optoelectronics frequency counters to drive the receiver... But more than
that, the screen of these receivers is too small, too few information...
I prefer being at home (or in a car) with a laptop computer displaying a
beautiful waterfall picture )

That's the reason why I owned a SDR-IQ. And on upper frequencies, it will
keep being useful with an appropriate scanner (if I see a cheap one on
the second hand market).

For the moment, I prefer exploring the bands than picking up a frequency
in a database (it may change...)

Sebastien.