On Sat, 6 Sep 2014, Lostgallifreyan wrote:

I'm not sure if this is 'homebrew' exactly, but close enough, maybe..

I was looking around via Google, but found allusions to rather than direct
sources, of an internal modification to allow the unused middle connector of
the antenna socket to allow an external AM antenna. I've not found the
article itself, or any pointer saying exactly where it is either. All I have
is a name, Laurie Mann, in Australia.

I'd already tried coupling a long wire directly to the AM input after
unsoldering the wire on tne non-grounded end of the winding on the ferrite
rod, with no meaningful improvement (as expected, it worked, but was too
noisy to be helpful in any way). While a car radio will take any bit of wire
as an antenna the PL-390's AM isn't meant to work that way. I'd already tried
doing that with the winding still soldered in place too, with no convincing
result.

IN the old days, they'd either suggest wrapping some wire around the
radio, grounding one side and the other going to the antenna. In other
words, a inductive coupling loop to the loopstick. The advantage of this
method is that it requires no modification, the disadvantage is that it
looks messy and may interfere with the controls.

So you open up the radio and put a few turns on the loopstick, grounding
one end and the other going to the antenna. It's the same thing, but no
messy outside loop (and in the case of a digitally tuned radio, winding
directly on the loopstick likely adds less noise than a winding around the
radio (which might pick up the noise from the radio).

It does make me wonder what is done in the average shortwave portable.
EIther the external antenna connector doesn't work on the AM broadcast and
LW bands, or they use some other scheme to couple to the rest of the
receiver on those bands. I don't have that sort of schematic handy.

The internal loopstick needs to stay as it is, since it's not just "an
antenna", but the tuned circuit at the front of the radio. Unless you
were going to get really fancy, and change the loopstick for a shielded
coil fo the same inductance, and then coupled the antenna to that.

Or, use a big external loop of the same inductance, and use that instead
of the internal loop, though in that case, it won't be so portable, and
you wouldn't want to have the loop any distance from the radio.



In short, I think the Tecsun PL-390's LW AM performance is a LOT better
than it is credited for generally, but all the same I'd like to have a
crack at seeing if I can hear an NDB from london to Bristol. I know,
little things please little minds. But it's a very fun way to learn
so I want to have at it, and I'm interested in anything anyone has to
say if they have worked on modifying this specific radio in any way.

The only reviews I've seen of that sort of radio are from here in North
America. An important consideration is that there is no long wave
broadcasting over here, so the LW band is mostly dead. The only thing
left down there is some airport beacons. I havent' spent much time tuing
LW, but all I've heard is the local airport beacon (and maybe the Ottawa
beacon, I wasn't completely sure). That was with a Grundig YB400,
shrotwave portables are the only LW receivers I've ever had.

But if you live in the land of LW broadcasting, that might change the
comments about the LW band being "dead", since it may not be the receiver,
but the lack of transmitters.

I have a Grundig/Eton G8 and I've not heard anything on the LW band, but
maybe I wasn't doing it right.

Michael