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Old 8th Oct 2014, 10:37 pm   #72
Phil G4SPZ
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Join Date: Apr 2005
Location: Bewdley, Worcestershire, UK.
Posts: 4,260
Default Re: Roberts RMB Problems

Quote:
Originally Posted by sobell1980 View Post
Obviously I have misunderstood the use of my sig gen at the RF stages. If anyone could run through what i should be doing with the sig gen on the RF side? What i should set my sig gen to etc and attenuation.
There is a wealth of helpful information on Paul Stenning's website, and you would be well advised to read the descriptive articles on basic superhet principles. Here is a good start on how the IF stages work.

The only reason I suggested 1MHz from the signal generator and 300m on the radio is that this will most likely be the way the equipment's dials are calibrated. As Pete says, 300 metres equals 1,000kHz and the numbers are easy to remember, as well as every broadcast radio will have this wavelength marked on the medium waveband. It's also a quiet spot on the band, at least hereabouts, and I set my pantry transmitters to this frequency.

The general rule is to keep the output from the signal generator as low as possible, commensurate with satisfactory reception. If you have to turn up the generator output to hear anything at all, it tells you that something's wrong. When you progress to aligning radios, a small input signal prevents the set's AGC from coming into action and reducing its gain.

Once you have got this radio working, a few minutes spent playing with the sig gen will quickly give you the idea. You have all the test gear now to perform a full alignment, and even if the set doesn't need it, you will learn a great deal by following the alignment procedure set out in the Trader service sheet.
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