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

I notice I made an error in describing the output of the varactor-tuned transformer--this isn't at the 455 kHz IF that I said, but is still the MW-band RF signal coming from the antenna. This is fed to the LA1260 IC which then does the conversion to the IF. I've revised my Review to show this--keep this one and delete the previous one. 
Steve
----- Original Message ----- From: "Steve Ratzlaff" <steveratz@xxxxxxxxxxxx> To: "Mailing list for the International Radio Club of America" <irca@xxxxxxxxxxxxxxxx> 
Cc: <jaypolicow@xxxxxxxx>
Sent: Monday, May 23, 2011 1:11 PM
Subject: 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 RF 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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