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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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#1 |
Tetrode
Join Date: Apr 2017
Location: Woodend, Victoria, Australia.
Posts: 62
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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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#2 |
Dekatron
Join Date: Mar 2012
Location: Fife, Scotland, UK.
Posts: 11,321
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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
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Can't afford the volcanic island yet, but the plans for my monorail and the goons' uniforms are done |
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#3 |
Tetrode
Join Date: Apr 2017
Location: Woodend, Victoria, Australia.
Posts: 62
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Interestingly the audio on my Eddystone 990R sounds great though, and I think it has a 30kHz filter for AM.
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#4 |
Tetrode
Join Date: Aug 2007
Location: Belfast, Northern Ireland, UK.
Posts: 60
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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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#5 |
Tetrode
Join Date: Apr 2017
Location: Woodend, Victoria, Australia.
Posts: 62
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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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#6 |
Tetrode
Join Date: Aug 2007
Location: Belfast, Northern Ireland, UK.
Posts: 60
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I made C269 & C239 both 4.7uF, simply because I had them to hand: sounds fine.
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