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Old 4th Apr 2012, 11:42 pm   #1
Sammyboy
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Default Sony ICF-SW1 'overloading' on FM?

My Sony ICF-SW1 seems to be easily 'overloaded' by spatter from Radio 1 and Classic FM. The previous owner said he'd replaced the faulty electrolytics but not sure if it was all 6 capacitors and what spec the replacements were. Could this affect FM performance? The aerial is damaged with the top section or two missing, could that contribute?

I'm asking as I'm not sure if this overloading is normal on SW1s or whether mine has an issue that's affecting sensitivity/selectivity.

Last edited by Brian R Pateman; 5th Apr 2012 at 8:41 am. Reason: Tidy up prior to moving to a different section.
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Old 5th Apr 2012, 10:29 am   #2
Darren-UK
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Default Re: Sony ICF-SW1 'overloading' on FM?

The first thing I'd do if in your shoes would be to suspect that aerial. You could extend it as far as what's left of it allows, then touch it (ie use your body as an aerial) to see if there's a significant improvement in performance.

The capacitor change indicates, obviously, that someone's been inside the radio so also check to see if the remains of the aerial are actually connected and, if so, are connected properly.

Having done that, get back to us with the results.
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Old 5th Apr 2012, 2:01 pm   #3
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Default Re: Sony ICF-SW1 'overloading' on FM?

Thanks for the reply Darren, the aerial does seem to be connected properly.

Touching the aerial has varying results depending on how the radio is held and the direction of the aerial - sometimes no noticeable effect, other times does improve the signal. It can cut through the spatter in certain angles but not others. Also sometimes just having my hand near the aerial is enough to improve the signal. Would this suggest it's the aerial that's at fault? I've looked in various places but can't seem to find a replacement aerial, I've been looking for faulty SW-1s to buy for spares but they tend to go for more than I paid for this radio!
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Old 5th Apr 2012, 2:29 pm   #4
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Default Re: Sony ICF-SW1 'overloading' on FM?

You are quite close to Sutton Coldfield so overloading might be a possibility. If so, shortening the aerial will help. It could be a sign that an internal stage is oscillating and so distorting the signal. If you were further away then multipath distortion could be the culprit.
I'm not sure electrolytics will have much effect at VHF frequencies.
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Old 5th Apr 2012, 2:57 pm   #5
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Default Re: Sony ICF-SW1 'overloading' on FM?

I'm very close to Sutton Coldfield TX, shortening the aerial does indeed help though can degrade the signal too. I used Radio WM 95.6 as the 'tester' station as this seems to suffer the most, oddly Free Radio (Ex-BRMB) on 96.4 isn't as badly affected. My older but larger ICF-7600D doesn't suffer from this at all but guess that's because it's got more efficient tuning circuits (and/or an intact aerial!)?
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Old 5th Apr 2012, 5:36 pm   #6
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Default Re: Sony ICF-SW1 'overloading' on FM?

The ICF-SW1 has a Local/DX switch that will attenuate the antennasignal when put in 'Local'.
That should take care of any overload-situation.
When it doesn't the problem is not caused by overloading the input RF-amp imo.
I believe this Sony is made with SMD-electrolytics with a reputation for going bad. Probably a re-cap could cure the problem.
I have the Service-Manual; PM me with your e-mail address for info.

rgds,

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Old 5th Apr 2012, 6:40 pm   #7
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Default Re: Sony ICF-SW1 'overloading' on FM?

A long time ago I remember looking at various of the smaller Sony portables. I did not buy one because I found that they suffered from being easily overloaded. So there is the strong possibility that you have encountered a design issue.

At the time I was puzzled by this performance, as in many countries the radio service comprised 'local' transmitters situated in or near the relevant city. Hence being able to pick up weaker signals in the presence of strong local signals would have been a common need (or so I thought!) for the advertised use of the receivers.

Last edited by SteveCG; 5th Apr 2012 at 6:41 pm. Reason: Typo and addition
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Old 5th Apr 2012, 7:16 pm   #8
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Default Re: Sony ICF-SW1 'overloading' on FM?

Switching to local unfortunately also attenuates the WM signal too sadly!

@tri-comp - The previous owner re-capped it apparently, the SW1 works fine on SW, LW and MW with no motorboating or other problems. Thanks for the offer of the service manual by the way!

@steve - I have a feeling the SW1 has a problem with strong signals - but with the state the radio was in I wanted to rule out any other problems. Didn't want to shell out for a new aerial (if I could find one!) to find it didn't cure or help the problem

It does seem odd though that a small, (then) premium-priced radio would suffer from this kind of problem on FM though I guess it's primary purpose was listening to the non-FM wavelengths. Still very fond of the battered little Sony though!
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Old 7th Apr 2012, 10:36 am   #9
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Default Re: Sony ICF-SW1 'overloading' on FM?

A thought: I wonder if the IF 10.7 Mc/s filter system is working properly? You mention splatter from strong-signal transmitters not too far removed in frequency. A failure in IF selectivity - especially on the outer IF response frequency skirts - can give this problem. The IF filter could be ordinary LC transformers or it could be a ceramic filter. I certainly have had problems in the past with such ceramic filters (or their driving circuitry) failing.
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Old 7th Apr 2012, 11:41 am   #10
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Default Re: Sony ICF-SW1 'overloading' on FM?

I do wonder if there's a problem in that area, sometimes it seems as if I have to tune up another 0.1Mhz on FM to get a better signal on some weaker stations. It does seem that Radio WM on 95.6Mhz is the worst affected by this, the spatter tends to be all over the 'dial' but worse in those middle sections.

I'm wondering about getting the SW1 sent off to be professionally refurbished, maybe see if they can source an aerial and battery cover too. I'm not proficient enough to do it myself, my soldering skills are certainly lacking!
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Old 7th Apr 2012, 11:54 am   #11
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Default Re: Sony ICF-SW1 'overloading' on FM?

Quote:
Originally Posted by G8HQP Dave View Post
You are quite close to Sutton Coldfield so overloading might be a possibility. If so, shortening the aerial will help. It could be a sign that an internal stage is oscillating and so distorting the signal. If you were further away then multipath distortion could be the culprit.
I'm not sure electrolytics will have much effect at VHF frequencies.
I totally agree with this. A few years ago we stayed at a hotel on Dartmoor with the high powered North Hessay Tor just a few miles away. My ITT Colt was totally overloaded with the telescopic rod extended by even just a couple of sections. If I fully retracted the rod aerial I could then hear the weaker FM stations from both Torbay and Exeter.
Some of the more modern FM portable sets cope much better as their front ends have a far wider dynamic range than that offered by many of the older sets.
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