TheRadioBoard

I have been looking at inexpensive solid state AM/FM receivers. I came across the following.

Sony SRF-59
Sony ICF-S10MK2
Sony ICF-38

I read for Ultra Portable the SRF-59 wins over the ICF-S10MK2.

My main question is does anyone know if the ICF-38 uses the CXA1129N from the SRF-59 or the CXA1019S from the ICF-S10MK2? If it uses the CXA1129N then this might be a wonderful radio to play with. The larger size might accommodate a longer ferrite rod or perhaps get rid of the AC cord storage area and use batteries larger than AA.

I am trying to find an ICF-38 locally and verify which chip it uses.


Thanks all.

Well, did not have one locally but I was able to get Sears to mail order one. I will verify which chip it uses and what size ferrite it has.

If the news is good this looks like a mod-job for Dr. Phil.

You might want to ask the folks over at the Ultralite dx group at Yahoo!.
http://groups.yahoo.com/group/ultraligh ... =293630128

Dave

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Amazon carries the ICF-38 (USD20.30) and all but one review are excellent. One reviewer noted that selectivity and sensitivity were impressive. I'd be interested in knowing two things when you open it:

1. Does the ferrite bar extend the width of the case?
Edit: Found the answer in the owner's manual. Judging from an illustration, the battery box extends to the top of the case, so the rod is probably at most 3.5-4 inches long. Here's the link:

http://store.sony.com/webapp/wcs/stores/servlet/ProductDisplay?catalogId=10551&storeId=10151&langId=-1&partNumber=ICF38#specifications

Look under Product Warranty for a link to the PDF manual.

2. If it uses a traditional mixing scheme with a tunable local oscillator, is the LO inductor on the same ferrite rod as the antenna?

I have a couple of portables in that size range, both vintage. If you overcouple an external antenna to the rod you detune the LO; one of these days I'm going to wind a separate LO inductor on a toroid to solve that problem. But the '38 is attractive because it covers the entire AM band, which neither of my vintage portables does.

73,

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KR1S,

If that's true (hard to tell from the angle) then I plan to relocate the battery box to where the AC cord is and do away with it. Maybe I can fit C or D batteries in there and then install a 200mm ferrite rod.

I think this is gonna be fun.

I like your idea regarding winding a separate toroid for the LO.

I will definitely be talking to you about some mods after it arrives.

Hey All,

Maybe a bit OT , but my favorite "Ultra Light" set up is my "Boy's" 2Q reflex pocket radio on a ("tough") "box" loop. This loop is literally built on a corrugated cardboard box ( 2' X 4 ' ?) lined with 1x1 pine strips.

The turns are #28 magnet wire spaced at 1/4" and simply poly'ed into place with multiple coats of poly. The var cap is a 4 gang ceramic wiper less.

Such a loop may not be the BEST design, but I like the fact that it is a BIG and fairly tough (re field transport purposes) and is always ready to go ( doesn't need to be field wound).

The fact that the cardboard is corrugated lets much of each turn stand on fairly thin paper. The wiper less ceramic var cap really works nice and the overall Q of this loop seems (by ear) "good to very good" (NOT top notch, but I feel quite happy with the trade off of utility vs Q).

The reflex does the coarse tuning but the fine tuning is done by the loop's var cap.The radio will except quite a wide range of tuning via the loop. In this case the "cart" (loop) leads the "horse" (radio) around by it's nose for quite a ways up or down the band.

Null is good due the size of the loop .Quite a bit of U.S. Dx ie WWL. I haven't tried anything more ambitious yet (ie the sunset transatlantic window from Cape Cod).

Phones are a great sounding pair of JVC stereos on a mono adapter.This set really NEEDS phones, the speaker isn't that great.

All told a nice little system, maybe not the typical HIGH END ultralight set up, but simple ,easy and fun.

K

Regardless, the price is low enough that you can write it off as a research project, no matter how it turns out. Let us know how it performs.

Here is a YouTube video that gives a good view of the Sony ICF-38.

Sony ICF-38 Review

I hope you can wrangle a schematic somewhere. Reviewing one of my old portables, a Zenith Royal 705, they used a separate inductor for the LO. The lineup is RF stage --> Converter (Mixer/LO) --> IF.



With a tuned external loop (Terk) coupled by several turns wrapped around the ferrite rod, the LO is pulled when the antenna is tuned to resonance. I'm now thinking the RF stage isn't isolated enough from the converter. You don't need a lot of coupling anyway, as the dynamic range of these radios isn't spectacular.

A longer ferrite rod is surely a good way to start, and a 7-inch rod will easily fit in the 9-inch-long case. The battery box looks to be molded right into the case, so good luck relocating it. Cutting the plastic and putting a 4-cell holder where the line cord stores is probably easy. AA cells are good enough; they'll last a long time. Stop by your local supermarket and look for a 9-inch Lazy Susan gadget. Makes spinning the radio to align the antenna a breeze, and they're only a few bucks.

73,

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http://qrp.kearman.com/

Saw your question to macrohenry in the other thread. People have had good results with radios based on a DSP chip made in Texas, though the radios are built in Japan. There are several models. Personally, I think the PL-380 is the best deal. DSP-filter adjustable selectivity, LW, MW, SW and FM (stereo), and runs on 3 AA cells. I modified one to work with an external loop antena, which the radio tunes.

http://kr1s.kearman.com/html/MULDxER.html
http://kr1s.kearman.com/html/hooploop.html

Using that external antenna adjusted for longwave, I've picked up several European and African broadcast stations on that band, too. MW and LW performance definitely benefits from a better antenna than the dinky loopstick inside the radio.

There's a Yahoo group for "ultralight radios," but they are antenna faddists. There's some good info on different models in their files section, though. The ICF-38 is too large to count as an ultralight, but still looks like a good radio, and it costs less than a PL-380, which runs about $55-$70 with shipping from China. Several eBay dealers carry them. Here's one item number: 250678429559

73,

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http://qrp.kearman.com/

Hehe it's funny you say that.

I have been looking at your hooploop for years and I plan to build a regen (possibly the G.W. Homodyne) using the hooploop as the inductive part of the tank. Plan on using a large 61 mix ferrite toroid core inside the receiver with a connector to quick disconnect the actual loop.

Right now I am looking for a good, inexpensive, modifiable radio to serve as a base comparison. I was very impressed with the reviews of the Sony SRF-59 as a DX radio. My research led me to the ICF-38 which looks to have great possibility to be a fine radio and much more modifiable, at least more easily done so. The reviews I have read on the ICF-38 are good but no reviews on any of the DX sites I can find and no information on what lurks inside its' chassis.

I figure the $25 I spent (free shipping) is well justified and might lead to some great mods for this little receiver.

Dr Phil did amazing things IMO with the SRF-59 and the ICF-S10MK2.

Right now I am looking at an Amidon ferrite rod 7.5" long, 0.5" diameter, mix 61 that looks great.

Besides Dr. Phil's web site at http://home.comcast.net/~phils_radio_designs/, also the site http://www.dxer.ca/ might be interesting. I remember some good articles of John Bryant. I thought I had read it at dxer.ca but the site seems to have seen a relaunch, so I do not find the articles of John Bryant there at this moment.

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73 de Fritz

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<b>Radio geht ins Ohr, Fernsehen ins Auge.</b>
<i>Robert Lembke (1913-1989)</i>

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I've never noticed any hand-capacity effects when moving the Hoop Loop. I think that's because the capacitance of the tuning cap is greatly magnified by the square of the transformer's turns ratio, so hand capacitance is small by comparison. One experimenter who used a smaller loop was a co-inventor of the DSP chip used in the Tecsun PL-380 and similar radios. He used a very small toroid inside the radio and was happy with it, but the PL-380 has DSP-based selective filters. For the homodyne you'd benefit from better Q in the matching transformer.

You may find that self-capacitance in the large winding makes it necessary to remove turns, but the calculated inductance worked out fine when I hooked up a 365-pF variable to one I use with a communications receiver. If you really wanted to optimize Q, you could use small Litz. Get the winding that connects to the loop well-centered and ground the center tap, to get the best performance. Looking forward to hearing how this works out.

73,

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http://qrp.kearman.com/

The Sony ICF-38 should be here Tuesday, I was so hoping it would be here by the weekend.

Yesterday I was driving by a farmer market and had to stop. In the distance I thought I saw a GE Superadio. Sadly it wasn't, it was a Panasonic RF-594 AM/FM receiver. I picked it up for 5 bucks and it works. Sounds pretty good too. Does anyone know anything about this model? My web searches have turned up nothing, not even a picture. It needs a lot of TLC and if it seems worthwhile I will recap it, looks like it is from the early 70's. I will try to upload some pics this weekend including the circuit board.

Thanks all.

Brother, we've all been there!

On that RF-594, couldn't even find one on eBay. I wonder if it was a model never exported to the States, that someone brought back from overseas. A $5 radio that works is a bargain anyday, IMO.

Re the Sony: Hope you get it before Sears closes the store!

73,

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http://qrp.kearman.com/