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#1
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Cobra 18 WX ST - TX Distortion
My brother in law and I were tuning a new antenna for his Cobra 18 WX
ST and when we got the SWR as low as we could, tried it out. As he got further away during a test run I encouraged him to speak up because he wasn't getting decent modulation. When he did the result was pulsating oscillations that obscured his audio. I'm an audio guy, but I mix rock concerts. The type of squealing I usually deal with is some jerk guitar player wanting 130 dB SPL from his monitor wedges. There's not any possibility for audio feedback in this case, my rig was two miles away from his and he doesn't have talkback. At any rate, the question is, would replacing the audio amp chip do the trick, is the part readily available, and is it anything a guy with plenty of soldering experience couldn't tackle. Thanks in advance... Jon |
#2
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Cobra 18 WX ST - TX Distortion
JonnyBNB wrote:
My brother in law and I were tuning a new antenna for his Cobra 18 WX ST and when we got the SWR as low as we could, tried it out. As he got further away during a test run I encouraged him to speak up because he wasn't getting decent modulation. When he did the result was pulsating oscillations that obscured his audio. 1:1 SWR does not mean resonance. It just means you've made the antenna about 50 ohms. You are probably getting RF down the shield of the coax and causing RF feedback. You need to decouple the antenna from the shield with a proper ground plane. Are you sure you didn't pull the ground loose from the base of the antenna or the crimped on PL-259? If this is a mobile installation on a trunk lip, don't trust the hinges to have a good RF ground. I guess this is a magmount? Since you didn't describe your antenna, we can't help any more then this. I'm an audio guy, but I mix rock concerts. The type of squealing I usually deal with is some jerk guitar player wanting 130 dB SPL from his monitor wedges. There's not any possibility for audio feedback in this case, my rig was two miles away from his and he doesn't have talkback. And I have hundreds of GB of lossless music and am a shn/circ manager at db.etree.org and also a moderator of a major BT site. When a famous old band played locally, the main man made sure I was on the guest list! At any rate, the question is, would replacing the audio amp chip do the trick, is the part readily available, and is it anything a guy with plenty of soldering experience couldn't tackle. No, replacing the amp chip won't help. Fixing the antenna's problem will. Try your local library for an ARRL handbook. It should be somewhere around 621. |
#3
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Cobra 18 WX ST - TX Distortion
On 6 Mar 2006 22:08:15 -0800, "JonnyBNB" wrote in
.com: My brother in law and I were tuning a new antenna for his Cobra 18 WX ST and when we got the SWR as low as we could, tried it out. As he got further away during a test run I encouraged him to speak up because he wasn't getting decent modulation. Are you sure the problem was lack of modulation and not lack of carrier signal strength? When he did the result was pulsating oscillations that obscured his audio. Motorboating? Sounds like it might be a power supply deficiency. I'm an audio guy, but I mix rock concerts. The type of squealing I usually deal with is some jerk guitar player wanting 130 dB SPL from his monitor wedges. There's not any possibility for audio feedback in this case, my rig was two miles away from his and he doesn't have talkback. I don't get too much monitor feedback, but then I work smaller rooms. When someone cranks their monitor it usually messes up the room's EQ and I have to dial in a compromise between the monitor and the PA. At any rate, the question is, would replacing the audio amp chip do the trick, is the part readily available, and is it anything a guy with plenty of soldering experience couldn't tackle. A new audio amp probably won't change anything. Check your power supply. You should be getting a steady 13.6 - 14 volts to the radio and it shouldn't change under full modulation. If the signal is weak, make sure your antenna is installed properly (good grounds & cable). Get a bigger antenna if necessary. ----== Posted via Newsfeeds.Com - Unlimited-Unrestricted-Secure Usenet News==---- http://www.newsfeeds.com The #1 Newsgroup Service in the World! 120,000+ Newsgroups ----= East and West-Coast Server Farms - Total Privacy via Encryption =---- |
#4
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Cobra 18 WX ST - TX Distortion
Thanks, grounded the deck lid and it's getting out much better.
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#5
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Cobra 18 WX ST - TX Distortion
JonnyBNB wrote:
Thanks, grounded the deck lid and it's getting out much better. Glad to hear it. It's always the simple stuff... |
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