On 07/09/14 10:06, Lostgallifreyan wrote:
Michael Black wrote in
news:alpine.LNX.2.02.1409062303070.10573@darkstar. example.org:

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).


Thankyou! I liked that idea so much I went without sleep and had at it. I
have no photo hosting but I'm willing to upload a picture of the doings if
there's a way to make it generally useful.

I now have a little over 100 turns of enamelled copper wire (a thickness
chosen to allow good current for lowest loss) on one end of the PL-390's
ferrite bar. One end is grounded, the other, after laying two layers of turns
around the rod in the same direction as the main winding, is soldered to the
unused middle connection of the 3.5mm RF input jack. The result is excellent
too, despite the huge amounts of ambient noise from computer, router, modem,
LCD touchscreen and all, I'm getting every NDB I have detected with the
single exception of the ghostly Southhampton 15nm range one. I thought I'd
lost Gloucestershire too but apparently it has changed frequency a tad, and
it's definitely there, clear if not strong. Once I get a chance to run a
longwire out on Ashton Court I think I might hear London Calling... (Good
album, that though I prefer X-Ray Spex. Never mind, long story...)

Anyway, this is in the city centre, close to sea level, using the 8m tall
external whip. I think once I get it tested out on open land 125m above sea
level with a longwire it will be a great deal more interesting than it was
out there before.

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 PL-390 does it by switching the local telescopic whip out of circuit when
the remote antenna jack is plugged in. The unused middle terminals would be
equally capable of this, but they're soldered together and I left them that
way, other than adding my own wire from the new coil. Neither the whip or the
external antenna socket are used by the AM wavebands (MW+LW with a remarkably
small gap where the emergency shipping signals used to be at around 500 KHz).
I think there are two separate inputs to the DSP IC, one for these AM bands,
and another for HF and VHF. It might be even more complex, but I don't know.
I want to avoid taking the radio apart any more than I did, it's extremely
fragile...

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.


Agreed. The shielded inductor is a nice idea, but the first idea is best for
me, as it does not compromise intended operation in any way all, but adds a
great deal to the PL-390's AM capability. Whether more or less turns than my
100 (approx..) would be better I'm not sure but I didn't see any signs of
overload when checking the Bristol airport NDB, and either it's not at all
critical, or I got lucky. What IS critical is a good ground...

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.


I think that's what the people discussing the Laurie Mann modification were
doing, but I didn't get enough of the original context to be sure. One guy
was certainly doing something with a 4' loop built using 1.5'' UPVC pipe. Not
as portable as I want. It could be great if I want to explore external
tuning though. (And a good excuse to use some very nice tuning capacitors.)
My original plan was to try a larger ferrite rod and coil, something more
like the multi-layered turns I've seen on old receivers, but tonight's work
has left me satisfied for now, and likely for some time, it will take several
attempts to figure out how far it will go.



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.


Apparently there are submarines, but only at around 30 KHz. Things are
allegedly better for US LW DX if you can get to an ocean. I read a web page
that suggested it might be more exciting than I can know. Having lots of LW
transmissions isn't the boon it might seem, the big ones swamp the band so
much the allocation is pretty much one per nation in Europe, though France
has three! Maybe you also get something I know of here but have not explored,
there's some kind of digital modulation at around 100 KHz (carrier) for
logistical stuff for roads and weather, for hauliers and such. Also MSF time
at 60 KHz but that's beyond any receiver I've had for a long time.

By the way, my dad had a Grundig Yacht Boy 210, an ancestor of your YB400. I
identified with it more closely than if it had been a family pet. It was
central to home life, we had no TV... Got to say I liked the Hacker radios
better though, for general listening. I intend to make a cabinet to mount
the PL-390, for home use, better sound, larger NiMH cells, etc. Sonically,
it's surprisingly close to hi-fi on VHF. I think it just might be the best
all-rounder receiver ever designed for mass marketing and low cost.

=============
Talking LW time signals ,the UK MSF 60kHz tx is now located at Anthorn
-Cumbria . Sig here in Scotland is pretty strong.
It is a bit different with DCF at 77 KHz located near Frankfurt a/M
-Germany .
Both Lidl and Aldi (supermarkets) sell radio controlled clocks on 77KHz,
but to get the radio time signal I have to place such a clock near the
window here in the north of Scotland (IO87AT)
A reliable signal seems to be available everywhere up to approx 1000 kms
from the tx
Do you receive DCF ,77 khz well on your rx ?

Frank , GM0CSZ

Frank GM0CSZ