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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 11th Dec 2010, 2:16 pm   #1
HEAVY747
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Default Airband Kit Radio Help!

I have built the attached circuit from kit but the output is unable to driver speaker but I am able to use earphone. Also when I peak L5 coil I get signals which sound over modulated and garbled with whining may oscillation. If I unpeak L5 I get stations but not picked up strongly - why is there this oscillation? The radio doe hiss in the output - this radio is supposed to be 0.5uV sensitve - can this be right? The output uses LM386 should I get hiss on 8ohm speaker?

Please see attachedments which also has circuit diagram:

Please make your comments and help!
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Old 11th Dec 2010, 8:12 pm   #2
Biggles
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Default Re: Airband Kit Radio Help!

It sounds like the circuit may be unstable. In my experience, the LM386 can have a quiescent hiss, but not particularly loud. If you are getting a loud hiss this may point to there being instability somewhere. Does the hiss vary with the volume control setting? If you can't use the loudspeaker there may be a fault in the wiring. It's worth having a good double check. Keep all wiring as short as possible also.
Alan
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Old 11th Dec 2010, 10:20 pm   #3
G8HQP Dave
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Default Re: Airband Kit Radio Help!

It could be a failure of AGC, so it is overloading. Peak L5, then use a smaller antenna. The circuit is not designed to cope with strong signals. You might be getting image interference from the mobile band.

The MC1350 has high gain and can be prone to oscillation. I'm not sure how best to correct that.
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Old 12th Dec 2010, 6:15 pm   #4
Biggles
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Default Re: Airband Kit Radio Help!

This circuit is similar to the Ramsey AR-1 kit from a few years back. One noteable difference in the circuits is the AR-1 has a 22K resistor across the primary of the IF coil connected between pins 1 and 8 of the MC1350. This may calm it down a bit. I built an AR-1 a long time ago and have since converted it to crystal single channel control and added an RF amp and it performs reasonably well as a monitor rx.
Alan.
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Old 12th Dec 2010, 6:48 pm   #5
HEAVY747
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Default Re: Airband Kit Radio Help!

I am in debt to all your responses - please could you advise if the circuit is designed wrongly and thus be unstable? What could I do to help get an output as this circuit will not drive a speaker the way it should.

Please please advise.

Many Thanks
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Old 15th Dec 2010, 10:49 pm   #6
Biggles
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Default Re: Airband Kit Radio Help!

Going back to the obvious things; check that all the components are in the right place and the right way round. Check for things like solder bridges shorting two closely mounted components together. Check that the battery is in good shape and has plenty of power in it. If the earphone output is working, check for incorrect wiring around the speaker. Does the speaker hiss go away when you plug the earphone in? The speaker is usually switched out when an earphone is plugged in. Kits can sometimes require a bit of time spent to get working to their full potential and I have often had to resort to using proper test gear to set them up properly. Is there a help contact provided by the kit manufacturer? A quick e-mail to them may save you an awful lot of time. Sorry I can't be of more help to you.
Alan.
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Old 16th Dec 2010, 7:36 am   #7
Martin G7MRV
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Default Re: Airband Kit Radio Help!

I agree with Biggles, firstly, recheck that all the components are in the correct places, the correct orientation, and that the solder joints are good.

Looking at the pictures, i dont see a connection on the board for the speaker. Are you plugging the speaker in the same socket as the earpiece? If so, when using the earpiece, do you have to turn the volume down to listen comfortably? The LM386 should certainly be able to drive a small loudspeaker (im actually using an LM386 in a homebrew HF airband receiver im building, and its nice and loud!) If you have to turn the volume UP with the earpiece, then suspect the audio amp, otherwise i would check the speaker wiring.

You could try tack soldering the speaker wires direct to the board, bypassing the socket, to rule out a problem with the socket.

I would solve this problem before moving onto the sensitivity/distortion issues.

Do you have any test gear more advanced than a multimeter? or would you be able to borrow a signal generator to test the kit against?


If all else fails, i'd be willing to take a look at it for you and run it up against my comms test set, if you cover the postage. However, i couldnt prioritise it so it could take a while! If you have a local constructor who could take a look that might be more practical

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Old 22nd Dec 2010, 7:15 pm   #8
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Default Re: Airband Kit Radio Help!

Excellent photos Heavy747. Any chance of one showing the underside of the PCB too ?

Sparky
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Old 23rd Dec 2010, 5:27 pm   #9
Martin G7MRV
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Default Re: Airband Kit Radio Help!

Quote:
Originally Posted by Sparky67 View Post
Excellent photos Heavy747. Any chance of one showing the underside of the PCB too ?

Sparky
Good idea Sparky. A view of the underside might show up a problem with the soldering. I dont wish to be disparaging in anyway to the builder, but having someone else look the soldering over might show up something you havent seen. Its very easy to miss a problem purely out of familiarity!

I would be almost certain that the problem is either a missplaced component or a soldering issue

Ive taught soldering in industry, and even i make the odd duff joint (then spend hours wondering whats wrong )
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Old 29th Dec 2010, 9:43 pm   #10
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Default Re: Airband Kit Radio Help!

Sorry for late reply due t work commitments - You are truely great GUYS and I am in your debt!! I have sent it back to Waters and Stanton by recorded delivery and it still has not reached them!!!


I look forward to letting you guys know what happens. Martin G7MRV are you building and airband too? Any chance of pictures please?


The Very Best To You All.
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Old 30th Dec 2010, 4:56 pm   #11
Martin G7MRV
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Default Re: Airband Kit Radio Help!

Quote:
Originally Posted by HEAVY747 View Post

I look forward to letting you guys know what happens. Martin G7MRV are you building and airband too? Any chance of pictures please?


HEAVY747
Hi,

yes, but its not of the same type. Yours is an AM receiver for VHF. The receiver im building is a Direct Conversion circuit for receiving SSB signals. Its designed to cover the 5MHz oceanic aircraft frequencies. Its a variation on the G-QRP clubs 'Sudden' receiver. Im building it 'manhattan island' style. No photos im afraid, but you'll find Suddens and versions of them all over the net!


Martin
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Old 30th Dec 2010, 8:08 pm   #12
HEAVY747
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Default Re: Airband Kit Radio Help!

Cheers Martin G7MRV and rest of you guys
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