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Author Topic: Icom 735  (Read 2478 times)
AL3K
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Posts: 8




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« on: January 06, 2012, 02:02:10 AM »

       Hello. I just purchased a icom 735. I performed an alignment per service manual. The only problem I am having is the USB is higher pitched the the LSB. I can use the bandpass tuning to lower the pitch but I would like to fix it the right way.  I doubled checked the BFO and BPT alinements. The Icom service letter says that if the BFO and BPT are correct then its probably the FL-30 filter. Do these go bad? Is there any other thing I can check? Any way to test the filter? I really don't want to fork out 100$ for another filter.
                                                                                                                                                                  Victor AL3K
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KC8Y
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Posts: 244




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« Reply #1 on: January 06, 2012, 05:02:54 AM »

AL3K---

There's an ICOM Service Center in St. Joseph, MI...

You might want to contact them first...

web is sarts.com  Phone at 269-429-2334; talk to: Matt Adrian;
ICOM Service Center--MI; 1792 Nash Dr.; St. Joseph,
MI  49085

Think they also have profile on eham.net

KC8Y
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KA5IPF
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« Reply #2 on: January 06, 2012, 07:52:28 AM »

Icom uses a "one size fits all" approach to carrier oscillator alignment. Set it to a certain frequency and be done, not considering the filter may not be perfect in it's passband and center frequency.

You can set it by ear or use a 2-tone generator. Just adjust the USB Car osc until it sounds right. Won't hurt anything.

If you want to try the 2-tone method go to a Kenwood service manual and follow their procedure. Basically 2 audio generators with the output combined and fed into the mic jack. The tx signal is monitored on a 'scope for a crossing pattern. If the filter bandpass is 2.4kHz wide I use 300Hz and 2700Hz, for 2.7kHz 200Hz and 2900Hz. If you want more bass and less highs shift down keeping the 2 frequencies 2400Hz (filter bandpass) apart IE: 150 & 2550, 200 & 2600.

It makes setting Car oscillators simple and easy. The only hard part is getting 2 audio oscillators with exactly the same level and then combining them to get a 5mv audio signal. On the Icom since they use a preamplified mic you may have to use 25mv to get adequate drive. Try it.

Clif
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AL3K
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Posts: 8




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« Reply #3 on: January 06, 2012, 08:32:41 PM »

"You can set it by ear or use a 2-tone generator. Just adjust the USB Car osc until it sounds right. Won't hurt anything."

Thanks. By ear worked fine for me.
                                                                                       Victor
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