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Old 4th Nov 2012, 8:13 pm   #1
Racalfanatic
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Default Eddystone EA12 Distorted SSB Audio.

Hi All,

I have noticed that the SSB audio is a bit distorted on my EA12. I have replaced all of the resistors in the product detector can and it did improve slightly.
Increasing the I.F. bandwidth does improve things but it makes the receiver too wide for listening to SSB signals. I have tried a new valve but it made no difference. I sometimes wonder whether the product detector is being driven too hard.

It is a superb receiver and, after an hour or so, it hardly drifts at all.

Thanks in advance,

Ian
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Old 4th Nov 2012, 11:55 pm   #2
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Default Re: Eddystone EA12 Distorted SSB Audio.

I think you are probably right about the overdrive or perhaps low input from the BFO. Does the quality improve as you reduce the RF or IF gain?
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Old 4th Nov 2012, 11:59 pm   #3
m0cemdave
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Default Re: Eddystone EA12 Distorted SSB Audio.

I wonder how you are adjusting the gain when listening to SSB?

If this has a similar product detector and gain structure to the 888A, then when receiving SSB the proper technique was to preset the audio gain about halfway up, then control the listening level with the RF or IF gain control with the AGC off. When using the RF / IF gain full up with the AGC turned on, the product detector will be overloaded.

HTH.
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Old 5th Nov 2012, 12:54 pm   #4
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Default Re: Eddystone EA12 Distorted SSB Audio.

Andy, Those is precisely the settings used with an HRO but using the BFO to inject carrier.
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Old 5th Nov 2012, 6:05 pm   #5
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Default Re: Eddystone EA12 Distorted SSB Audio.

Hi Ian,

Have you checked the alignment of the IF filters and their bandwidths at the different settings. I have found these not easy to setup. You could have too much inherent IF gain. Remember the coupling is adjustable mechanically check nothing is slipping or it has been "fiddled" with

Does the slot filter work as it should ?

Kind regards
Mike
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Old 6th Nov 2012, 10:28 pm   #6
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Default Re: Eddystone EA12 Distorted SSB Audio.

Thanks for your replies. I have not done any realignment apart from making the VFO track more accurately.
Reducing the IF or RF gain does help but the audio still has "rough edges" and this gets worse after the set has been on for some time.
The receiver does seem to be really sensitive, even on 10 Metres!
I find it noisier than my 888A, but I think it's down to the increased gain in the I.F. stages. The slot filter works very well but it is very sensitive to small adjustments.

Thanks again,

Ian
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Old 6th Nov 2012, 11:59 pm   #7
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Default Re: Eddystone EA12 Distorted SSB Audio.

Ian,

If you are sure of the IF stages I would also check the AGC.

Does the S meter read accurately with a known signal level on the RF input.I am presuming you have a manual.

Mike
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Old 7th Nov 2012, 10:29 am   #8
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Default Re: Eddystone EA12 Distorted SSB Audio.

Could be worth checking that your BFO/CIO is giving enough output: a drifted-high anode resistor will reduce the amplitude of the carrier-injection by quite a bit (I had this on a CR100 many years ago).

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Old 7th Nov 2012, 12:30 pm   #9
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Default Re: Eddystone EA12 Distorted SSB Audio.

Eddystones are very prone to many resistors going way out of spec.
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Old 7th Nov 2012, 9:55 pm   #10
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Default Re: Eddystone EA12 Distorted SSB Audio.

Quote:
Originally Posted by MichaelR View Post
If you are sure of the IF stages I would also check the AGC.
Does the S meter read accurately with a known signal level on the RF input.I am presuming you have a manual.
Hi Mike,

Thank you for your input.

I don't have access to a calibrated signal generator but the meter does seem to give, what I would consider to be, reasonably appropriate readings.
I would have thought that the radio would distort on strong AM signals if the AGC was at fault and this is not the case.
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Old 8th Nov 2012, 1:20 am   #11
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Default Re: Eddystone EA12 Distorted SSB Audio.

Hii Ian,

When I setup the filters on my EA12 I did it with a swept analyser.Apart from the If there is also a bandpass filter which tracks the VFO, it uses 2 Vinknor inductors , it would be worth checking those to make sure they are setup correctly.There is an IF output socket on the rear, this is a buffered output from the IF that can be a useful check point to try and see what is happening with a spectrum analyser.

I would also make sure that all "covers" are in place for checks, they do make a difference.

Mike
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Old 7th Feb 2016, 3:33 pm   #12
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Default Re: Eddystone EA12 Distorted SSB Audio.

Another thing to note on the IF alignment of these sets is then you peak the IF in the narrow selectivity, you may find a double hump in the wider settings. I aligned mine set to SSB and it seems to give the best of both worlds.
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Old 7th Feb 2016, 9:56 pm   #13
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Default Re: Eddystone EA12 Distorted SSB Audio.

Remember that for SSB reception you need to drive these receivers differently to how you'd receive full-fat DSB-and-carrier AM.

You can't use AGC; rather - turn the RF Gain down, wind the AF Gain fully up, then gently advance the RF Gain and tune to resolve your desired signal.

If you just go ahead with the RF Gain set fully-up you'll overload the product-detector and never manage to receive anything sensible.
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