J.I.L. SX-400 receiver/scanner - audio mod? - UK Vintage Radio Repair and Restoration Discussion Forum

Damien VK3RX · 4th Dec 2017, 2:39 am

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.

Radio Wrangler · 4th Dec 2017, 7:13 am

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.

David

Damien VK3RX · 5th Dec 2017, 6:15 am

Interestingly the audio on my Eddystone 990R sounds great though, and I think it has a 30kHz filter for AM.

greenkit · 8th Dec 2017, 6:24 pm

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.

Damien VK3RX · 9th Dec 2017, 3:22 am

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.

greenkit · 14th Dec 2017, 11:12 pm

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

4th Dec 2017, 7:13 am	#2
Radio Wrangler Dekatron Join Date: Mar 2012 Location: Fife, Scotland, UK. Posts: 11,321	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. David __________________ Can't afford the volcanic island yet, but the plans for my monorail and the goons' uniforms are done

5th Dec 2017, 6:15 am	#3
Damien VK3RX Tetrode Join Date: Apr 2017 Location: Woodend, Victoria, Australia. Posts: 62	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. __________________ Damien http://www.vk3rx.com/

8th Dec 2017, 6:24 pm	#4
greenkit Tetrode Join Date: Aug 2007 Location: Belfast, Northern Ireland, UK. Posts: 60	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.

9th Dec 2017, 3:22 am	#5
Damien VK3RX Tetrode Join Date: Apr 2017 Location: Woodend, Victoria, Australia. Posts: 62	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. __________________ Damien http://www.vk3rx.com/

14th Dec 2017, 11:12 pm	#6
greenkit Tetrode Join Date: Aug 2007 Location: Belfast, Northern Ireland, UK. Posts: 60	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.