1. Where should the Audio attenuator AND RF attenuator be set at?
2. What should the meter (at the outout voice coil) be set at? ie a/c volts or do I need a a/c mv meter.
3. Would a sweep generator and an oscilloscope be better to align the stages?
Unless this is some very exotic receiver, like a Collins 390, I would just put audio modulation ON along with the RF, and peak the audio signal by ear using the set's own speaker. Start with relatively low settings on the RF and audio modulation, and then jack them up until you can hear the signal with the set's volume control set at normal listening level. You can rock the generator's freq knob back and forth until you hear the tone.
After you've got the IF xmfrs peaked, touch up the oscillator setting so that stations come in more or less where they belong on the dial.
No need for a sweep generator or 'scope using the above method. Piece of cake.
:When aligning the IF and RF stages (AM)with a Signal generator:
:
:1. Where should the Audio attenuator AND RF attenuator be set at?
:
:2. What should the meter (at the outout voice coil) be set at? ie a/c volts or do I need a a/c mv meter.
:
:3. Would a sweep generator and an oscilloscope be better to align the stages?
Tune your antique radio to a station known to be broadcasting on, say for example, 700 kHz. Now with your portable radio, tune back and forth around 700 + IF. If the IF is 455, then scan the portable radio's tuning back and forth around 1155 kHz until you pick up the whistle of the antique radio's oscillator.
Adjust the antique radio's oscillator so that the whistle heard exactly at 1155 kHz on the digital radio.
Now peak up the IF xfmrs, by ear, using a broadcast station and the antique radio's own speaker.
You're finished.
:When aligning the IF and RF stages (AM)with a Signal generator:
:
:1. Where should the Audio attenuator AND RF attenuator be set at?
:
:2. What should the meter (at the outout voice coil) be set at? ie a/c volts or do I need a a/c mv meter.
:
:3. Would a sweep generator and an oscilloscope be better to align the stages?
Now, regarding sweep generators, these are only required for FM. Regarding band width, this has absolutely nothing to do with stereo or mono. Although AM stereo is broadcast in some areas, most AM radios are mono. Increasing their band width won't make them stereo. Stereo is the broadcast of two separate audio signals encoded into one radio signal. Only with special decoding networks are you able to decode this stereo.
What band width passage does is it controls how selectively your radio tunes. It also controls the fidelity of the music. AM radios are always peaked. This allows maximum separation between stations. You can stagger your IFs like Peter said, for better fidelity. Closely spaced stations will interfere with eachother, though, because your radio won't be as selective. Usually, when you peak an AM radio's IF transformers, you'll get very nice fidelity anyway. It is common practice to peak AM IF transformers.
Where you do use a sweep generator is in FM. Here, the FCC has ruled that stations be spaced far enough apart that a radio can be less selective, which will allow for better fidelity. Also, an FM radio works by shifting its frequency back and forth to the ups and downs of each wave of music or speach. The louder the audio passage, the more dramatic the shifting in the transmitted frequency. If your FM radio isn't capable of passing the entire range of frequency shift, really loud passages will distort, and audio fidelity will suffer. With FM, especially with the discriminator, the bandwidth is analyzed on an oscilloscope, and a sweep generator is used to feed the various RF circuits. The circuits are then adjusted so that there is an appropriate flat or mesa to the middle of the band width.
.......And that doesn't even get you FM stereo, though improper band width will chop out information necessary for decoding FM stereo.
Thomas
http://www.antiqueradios.org/gazette/align.htm
Radiodoc
T.
::Thomas
:
:http://www.antiqueradios.org/gazette/align.htm
:
:Radiodoc
:
A site that may be of interest to you and others is
http://www.pmillett.com/tecnical_books_online.htm
On another note, while cleaning up the shop, I found an old Zenith metal escutcheon. I have no idea what model it fits. It looks like it was used with a chassis that had a drum type of dial. I have a scan of it if you are interested and want it. I am sure it could use another home.
Radiodoc
An AM reciever has peaked IF's, they're just there for RF amplification. They need to be as sharply tuned as possible to have good signal selectivity. The BAND tuning is done in the RF, oscilator, and converter stages.
Broadband IF's are necessary in FM sets where the modulation takes place over a range of frequency.
:The way I understand it is bandwidth is the range of frequencies occupied by a modulated carrier wave. Hence not all of the freq.s are 455khz. There is a high, med and low. Right? If they were all tuned at 455 it would be mono. That is where the sweep generator comes in, it oscillates between those freq's. Tuning the various freq's I think would give you maximum performance.
http://pcbunn.cithep.caltech.edu/jjb/Hammarlund/if_alignment.htm
Finally, if all else fails, be sure to ground the generator's chassis so that all radiant hum is bypassed to ground. Of course never ground a signal generator when doing work with radios, especially AC/DC radios, but it might be necessary when using it with a frequency counter.
Thomas
All equipment should be on a floating or ungrounded system when working on AC/DC radios.
I have the radio and the test equipment all connected to power with an isolation transformer.
<>
It must be related to the front end input processing circuitry of the freq counter that you are trying to use.
What Brand and model is the unit ? If you have tried coupling in through an isolative, ~.001 ufd cap
and brought the sig generators output attenuator level progressively upwards, at some threshold, that
counter should start responding with a reading.
As for the response of Sir Thomas, he was merely referring to the turning off of the 400~, 1Khz~, ? ~
modulation signal of the generator….so that only a continuous amplitude of CW carrier is present.
With the modulation on there would be an up and down variance of the RF output level at each
crest and node of the modulating signal. Quite a challenge for a counter to respond to if it uses a
minumal input circuitry design. BUT… within the means of some of the better HP’s, Tek’s, Syst Donners
with DC AC input modes as well as triggering mode and level adjustments along as threshold sets, and
HF/ LF rejection….all of which can be individually tailored to the incoming RF signal thus being in the order of
custom setup as a modern triggered scopes capabilities.
With that counter that you have, I might suggest a test to evaluate it of you happen to have, or access to, a tube
FM receiver. In its RF signal flow path, just after its mixer stage you will have its derived 10.7 Mhz IF signal and
you might monitor it at both the 1st grid circuit and the plate circuit of the 1St FM RF stage with the mentioned .001 ufd isolation capacitor at the end of the shielded lead into the counters input. There would be two distinct level thresholds at both test points, thereby evaluating the counters sensitivity. Then you would move further down to the point where you have the limiter stage, that is just before the detector circuitry following it. Now at this point you are not going to have the prior RF signals gradual Gaussian sinusoidal rise, but instead the transformation of that sine signal into a distinct square wave by the high stage gain and a flat topping out of the waveform. This is particularly dominant at the plate of the final limiter. So by this time I believe that your freq counter would have liked one of the four levels and types of signals experienced and responded with readout. If the unit did not respond until the final stages, it appears that to utilize the unit for freq measurement, that you would have to construct an off board plug in accessory in the effect of a wide band preamp and squaring circuit to attain that input that your counter responds to.
HOWEVER…if that scope(s) of yours is of some merit, I can tell you a manner in which to use it in order to accomplish the task if you will merely inform me as to its brand and series…..(and its not some unknown off the wall unit.)
<>
True, that set is one of the better designs of older communications receivers. The sweep generator alignment
of that unit would be more desirable for the observation of the side slope response of the IF passband and
ascertain that the alignment would be balanced off center frequency . Thereby assuring an equal response on
upper and lower sideband when being used in Single Sideband mode of reception. Otherwise a sharp tuning
with steep side slope response would be the desired performance tuning when wanting to attenuate nearby …interfering signals in Ham band use.
A far as your common AM…. AA5 radio….. 1 IF stage receiver, its use probably would only come into
play if you were to want to widen the pass band of the IF and enhance the 5kc bandwith extremes of response
and additionally “pep up/enhance” the treble levels of incoming audio. You do have 4 tuned circuits in the IF stage
and it would then be much easier to see the interaction of the four adjustments , and be certain of the final
response curve obtained.
73’s de Edd
Three touch topics:
““““I am unable to use a digital freq. counter with my tube signal generators to get a reading.”””””
It must be related to the front end input processing circuitry of the freq counter that you are trying to use.
What Brand and model is the unit ? If you have tried coupling in through an isolative, ~.001 ufd cap
and brought the sig generators output attenuator level progressively upwards, at some threshold, that
counter should start responding with a reading.
As for the response of Sir Thomas, he was merely referring to the turning off of the 400~, 1Khz~, ? ~
modulation signal of the generator….so that only a continuous amplitude of CW carrier is present.
With the modulation on there would be an up and down variance of the RF output level at each
crest and node of the modulating signal. Quite a challenge for a counter to respond to if it uses a
minumal input circuitry design. BUT… within the means of some of the better HP’s, Tek’s, Syst Donners
with DC AC input modes as well as triggering mode and level adjustments along as threshold sets, and
HF/ LF rejection….all of which can be individually tailored to the incoming RF signal thus being in the order of custom setup as can be attained with a modern triggered scopes capabilities.
With that counter that you have …..(BTW, which is a what?), I might suggest a test to evaluate it of you happen to have, or access to, a tube FM receiver. In its RF signal flow path, just after its mixer stage you will have its derived 10.7 Mhz IF signal and you might monitor it at both the 1st grid circuit and the plate circuit of the 1St FM RF stage with the mentioned .001 ufd isolation capacitor at the end of the shielded lead into the counters input. There would be two distinct level thresholds at both test points, thereby evaluating the counters sensitivity. Then you would move further down to the point where you have the limiter stage, that is just before the detector circuitry following it. Now at this point you are not going to have the prior RF signals gradual Gaussian sinusoidal rise, but instead the transformation of that sine signal into a distinct square wave by the high stage gain and a flat topping out of the waveform. This is particularly dominant at the plate of the final limiter. So by this time I believe that your freq counter would have liked one of the four levels and types of signals experienced and responded with readout. If the unit did not respond until the final stages, it appears that to utilize the unit for freq measurement, that you would have to construct an off board plug in accessory in the effect of a wide band preamp and squaring circuit to attain that input that your counter responds to.
HOWEVER…if that scope(s) of yours is of some merit, I can tell you a manner in which to use it in order to accomplish the task if you will merely inform me as to its brand and series…..(and, its not some unknown off the wall unit.)
“““I looked at that schematic, its a multi staged IF””””
True, that set is one of the better designs of older communications receivers. The sweep generator alignment of that unit would be more desirable for the observation of the side slope response of the IF passband and ascertain that the alignment would be balanced off center frequency . Thereby assuring an equal response on upper and lower sideband when being used in Single Sideband mode of reception. Otherwise a sharp tuning with steep side slope response would be the desired performance tuning when wanting to attenuate nearby …interfering signals in Ham band use.
A far as your common AM…. AA5 radio….. 1 IF stage receiver, its use probably would only come into
play if you were to want to widen the pass band of the IF and enhance the 5kc bandwith extremes of response and additionally “pep up/enhance” the treble levels of incoming audio. You do have 4 tuned circuits in the IF stage and it would then be much easier to see the interaction of the four adjustments , and be certain of the final response curve obtained.
73’s de Edd