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

["Steve Ratzlaff" <steveratz@xxxxxxxxxxxx>]

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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