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Vintage Amateur and Military Radio Amateur/military receivers and transmitters, morse, and any other related vintage comms equipment.

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Old 4th Dec 2017, 1:39 am   #1
Damien VK3RX
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Default J.I.L. SX-400 receiver/scanner - audio mod?

Has anyone done the audio mod included in the service manual (extract attached)?

My radio doesn't have it, and for anyone who has done it, I'm wondering what improvement it adds.

I mainly listen to airband and the comms are quite "muddy" not crisp, not unexpected given that these days such comms are fairly narrow (4kHz?) vs when the receiver was manufactured, hence its wide filter.
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File Type: pdf Extract SM JIL SX-400.pdf (39.2 KB, 51 views)
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Old 4th Dec 2017, 6:13 am   #2
Radio Wrangler
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Default Re: J.I.L. SX-400 receiver/scanner - audio mod?

There are various compulsory change-over dates for aircraft around the world to have changed to "8.33kHz" channel spacing radios. Their transmitters have to have a 300-2800Hz audio filter which definitely dulls the sound.

They also have a similarly tight audio passband on receive to be compatible with the multicarrier systems. Using a modern aviation radio, there is a decided difference in audio quality between what you hear off-air and that via the intercom function.

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Old 5th Dec 2017, 5:15 am   #3
Damien VK3RX
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Default Re: J.I.L. SX-400 receiver/scanner - audio mod?

Interestingly the audio on my Eddystone 990R sounds great though, and I think it has a 30kHz filter for AM.
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Old 8th Dec 2017, 5:24 pm   #4
greenkit
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Default Re: J.I.L. SX-400 receiver/scanner - audio mod?

Recovered air-band AM audio on my SX-400 was also quite poor (woolly...) until I did the mod: there's a definite improvement afterwards, though it's still not up to the quality from an Icom IC-R7000. The radio is easy to work on and the mod is straightforward, so it's worth doing. Mine has been doing sterling service as a bench monitor for many years.
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Old 9th Dec 2017, 2:22 am   #5
Damien VK3RX
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Default Re: J.I.L. SX-400 receiver/scanner - audio mod?

Thanks for this - much appreciated.

I note the mod says a couple of the caps can be any value 2.2 to 10mfd. The latter might increase the bass, so 2.2mfd might be the first to try.
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Old 14th Dec 2017, 10:12 pm   #6
greenkit
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Default Re: J.I.L. SX-400 receiver/scanner - audio mod?

I made C269 & C239 both 4.7uF, simply because I had them to hand: sounds fine.
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