Re: [IRCA] Technical Review: CCrane CCRadio-EP AM/FM Analog Portable Radio

[d1028gary@xxxxxxx]

Hello Steve (and all),

Thanks for the excellent CCRadio-EP technical review, Steve.

Tecsun apparently first introduced this two Litz-wire lead, 
multi-section loopstick coil system in the PL-310 Ultralight model, and 
has continued it in the PL-380 and PL-606 models. Why the Chinese 
factories have come up with this loopstick coil arrangement is a 
mystery, since simple replacement of the Chinese Litz wire (on the same 
ferrite bar) with higher-quality 40/44 Litz wire in a single coil (of 
the same inductance) willl always result in a dramatic signal 
improvement on both the MW and LW bands in all these radios. I don't 
know if the same would hold true in the CCRadio-EP, but if the Litz 
wire is like that in the Tecsun ULR models, this simple $5 modification 
would be worth a try.

73, Gary

<<<  The EP radio
does have what appear to be four separate coils, but they are simply
one
continuous coil that's been separated into four sections and spaced out
over
the loopstick instead of the traditional single coil centered in the
middle
(or sometimes offset) of the loopstick. The latest Tecsun pocket radios
such
as the PL-606 are also using a similar loopstick, with the single coil
separated into three sections and spaced over the loopstick. Apparently
this
is supposed to do something useful, but my own experiments show no
difference in AM sensitivity over the full tuning range whether it's a
traditional no-space coil or spaced-out in sections like the EP and
newer
Tecsun ULRs use on the loopstick.   >>>



-----Original Message-----
From: Steve Ratzlaff <steveratz@xxxxxxxxxxxx>
To: Mailing list for the International Radio Club of America
<irca@xxxxxxxxxxxxxxxx>
Cc: jaypolicow <jaypolicow@xxxxxxxx>
Sent: Mon, May 23, 2011 1:12 pm
Subject: [IRCA] Technical Review: CCrane CCRadio-EP AM/FM Analog
Portable Radio

Recently looking at Jay Allen's (of RadioIntel) new webpage
http://radiojayallen.com/, I read his review of the new C.Crane
CCRadio-EP
AM/FM analog portable radio and was intrigued by the mention of it
using the
"Twin Coil Ferrite Antenna" along with Jay's picture showing the
internal
loopstick with 4 coils on it. I bought a $10-off "orphan" from C.Crane
and
have taken it apart and now have a good idea of its operation. I first
tried
it out for AM reception, outdoors. I have an old GE SuperRadio II and a
Panasonic RF-2200 that both have larger loopsticks, as well as a Tecsun
PL-380 ULR that I've modified with an external Amidon 7.5" MW
loopstick.
(Jay did a much more extensive operating review and I recommend you
read his
review.) My sensitivity tests used just the modified PL-380 compared to
the
EP radio as I've found the modified PL-380 is the winner for weak
signal
sensitivity (barely) when tested against the other radios. I live in a
rural
area with no strong MW stations nearby--my tests are mostly limited to
weak
signal sensitivity and selectivity. The EP radio acquitted itself very
well,
though it couldn't hear some very weak stations next to stronger ones
that
the PL-380 could, possibly due to the narrower bandwidth filter
selection in
the PL-380, which I keep set at the minimum nominal 2 kHz setting.

Technical Details
I'm more of a technical geek than a MW DXer and I primarily bought the
EP
radio to try to learn something about its internal design, especially
as
related to CCrane's statement that it uses the "Twin Coil Ferrite
Antenna"
as well as the special fine-tuning control.
The EP is a full-size analog portable radio with a nice 5 inch speaker;
it
uses four D cells. As such it is similar to the old GE SuperRadio as it
also
has no digital tuning display. The EP radio has a full-size 200 mm
ferrite
rod loopstick. Twin connections for an external AM antenna (antenna and
ground) as well as an F connector for an external FM antenna are
offered. A
switch disconnects the internal AM loopstick for use of an external AM
antenna. Two separate AM filters can be selected with the front panel
switch, "Music" and "Voice". These are 455 kHz 6 element "LTM455W" type
small ceramic filters. The music filter is an F type, which is +/- 6
kHz
bandwidth (12 kHz); the voice filter is an I type, with +/- 2 kHz
bandwidth
(4 kHz). There are separate treble and bass controls. On the side of
the
radio are the Tuning and Volume knobs, but in the middle is a new
control,
which C.Crane has labeled "Twin Coil Ferrite AM Fine Tuning". In their
catalog they describe this as:
"for the very weak AM stations, reception can sometimes be fine-tuned
with
manual adjustment of our built-in "Twin-Coil Ferrite Antenna". However,
you
do not have to adjust the TCF Knob to receive outstanding AM
performance."
This is a control that can be turned counterclockwise a half turn and
clockwise a half turn, with a center detent position labeled "Normal
Position".
AM and FM Mono or FM Stereo can be selected; the headphone jack is
stereo. A
sliderule type tuning display is used with a vertical pointer that
moves,
and a bright LED backlight can be turned on if needed (and left
on--there's
a separate switch that turns it on and off).

I was eventually able to learn quite a bit about the internal design.
"Redsun" is marked on the printed circuit board, so it appears Redsun
builds
this radio for C.Crane, or at least designed it. (Most of my
exploration was
to learn about the AM section.) As C.Crane's literature mentions, it's
a
single-conversion superhet with 455 kHz IF. It's a TRF type, with the
loopstick tuned by a varactor, going to a dual gate mosfet RF
amplifier. The
external AM antenna input is untuned but has a separate dual gate
mosfet RF
amplifier. An antenna switch electronically selects the desired AM
antenna
input and turns on the appropriate RF amplifier. The outputs are
similarly
selected and sent to a varactor-tuned-output first IF transformer. The
signal is then sent to a dedicated Sanyo LA1260 IC which has combined
AM and
FM internal circuits--RF, oscillator, mixer, IF and detector stages,
separate for AM and FM. (You can find the datasheet for this IC on the
internet.) The detected output is sent to a stereo preamp/power amp IC
which
had a metal heat sink over it--I wasn't able to learn what type that IC
was.
As mentioned, a 5 inch 8 ohm speaker gives good sound, or stereo
headphones
can be used to get dual channel Stereo FM.
One interesting thing about the EP is there is no traditional
mechanical
variable tuning capacitor--everything is done with varactor diodes. The
Tune
knob is a pot which controls the tuning voltage going to the varactors.
There are 3 varactors for the AM section--two for signal tuned circuits
and
one for the local oscillator. (The FM input section is enclosed under a
shield--I couldn't tell anything about it without removing the shiled
which
I didn't do.)
Now for the special "twin coil ferrite AM fine tuning" control. I was
eventually able to trace enough of the circuit and figure out that this
is
connected to the two signal tuned circuits varactors and indeed gives a
fine
tuning control separate and independent from the normal tuning voltage
from
the Tune knob. Contrary to what C.Crane states, it tunes both the
loopstick/RF amp input but also tunes the output of the first IF
transformer
going to the RF input stage of the LA1260 IC. My guess is since it's
difficult to get correct tracking over the entire MW tuning range when
using
varactors (due to the difficulty of precisely matching them), this
control
was added to be able to peak the signal no matter where the radio is
tuned.
In my outdoor listening tests, it was definitely needed below about
1000
kHz; with hardly any effect noted above that where it could then be
left in
the center-detent "normal" position.
Another variance with what C.Crane says about the radio is the
loopstick. It
is not a "twin-coil" loopstick. It's just a traditional tuned
single-coil
unbalanced loopstick feeding the following RF amp. In fact one end of
the
loopstick is grounded directly to the PCB groundplane. A real
"twin-coil"
type of loopstick such as is used in the C.Crane patented "Twin-Coil
Ferrite
AM Antenna" uses two isolated coils, one on each side of the loopstick,
fed
to a metal can slug-tuned RF transformer where they are combined in
series,
with the output of the transformer then going to an RF amp. The EP
radio
does have what appear to be four separate coils, but they are simply
one
continuous coil that's been separated into four sections and spaced out
over
the loopstick instead of the traditional single coil centered in the
middle
(or sometimes offset) of the loopstick. The latest Tecsun pocket radios
such
as the PL-606 are also using a similar loopstick, with the single coil
separated into three sections and spaced over the loopstick. Apparently
this
is supposed to do something useful, but my own experiments show no
difference in AM sensitivity over the full tuning range whether it's a
traditional no-space coil or spaced-out in sections like the EP and
newer
Tecsun ULRs use on the loopstick. But at any rate the loopstick in the
EP is
not a "twin coil" even though it's a full-size 200 mm rod and does a
good
job with good sensitivity. (My EP loopstick measured 272 uH, since I
unsoldered it and measured it.)
I like the EP--being a purely analog radio it doesn't suffer from all
the
various beeps and squawks and spurious sounds that you hear with the
Tecsun
ULR DSP radios that I've been using lately. It's a fullsize portable
radio
that should give long life from its D cells, especially if you listen
with
headphones. Its sensitivity was close to my best MW radio, with its
large
200 mm loopstick. I can't comment on how well the FM compares to other
radios; I don't spend much if any time in FM mode when using portable
radios. If you can do without a digital display, then I think you too
would
be happy with this radio. And I think it could also be considered a
worthy
successor to the discontinued GE SuperRadio.

Steve Ratzlaff

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