Technical question please - UK Vintage Radio Repair and Restoration Discussion Forum

gezza123 · 17th Jan 2011, 5:57 pm

HI,Guy's
I have a Taylor 67a Signal Generator,and the dials or marked in (-dB)IE: 0 -20 -40 -60 -80 the RF output is (0 to 10).The max output seems to be 100Mv.
Ive been trying to do a Stage-Gain test.
The I.R.E says the standard set for stage-gain is set to 50mw.ac across the audio output transformer.
So I have set up my radio and get 50Mw.or 16volts ac on the meter with the controls set up and the oscillator muted,and the signal is fed into the grid of the converter so am I correct in my working results.

The generator is set for -40dB and the RF is set to 6.
I have worked it out as 100mv-40dB = 60X10 = 600 x 6=3600uv/50Mw =72.is this about the correct gain of my radio .
Thank you for your comments.Gezza

ppppenguin · 17th Jan 2011, 6:06 pm

There's a lot of confusing numbers here. What's all the megawatts and megavolts for? I'll assume you mean milliwatts (mW) and millivolts (mV). How on earth does 16V correspond to 50mW at the output? That would only be true if the impedance is over 5kΩ. Are you by chance measuring at the primary of the output transformer perhaps? In which case do you know the ratio of said transformer so that you can calculate the impedance at the primary?

Other questions. What is the AGC up to? Have you disabled it? Is there any overloading? There shouldn't be at 50mW but it's nice to know for certain. The actual output level is not important if you are measuring gain, provided that there is no overloading and you are aware of what the AGC is up to.

Station X · 17th Jan 2011, 6:45 pm

Quote:

The generator is set for -40dB and the RF is set to 6.

Can you explain this please. Most signal generators operate at a fixed level and are followed by an attenuator. I'm guessing that the dB or is it dBm figures refer to the attenuator, but what does RF (range 0 to 10) refer to?

Skywave · 17th Jan 2011, 7:10 pm

I really cannot understand just what it is that you are trying to measure. You refer to 'Stage gain'. Which particular stage in this radio are you trying to determine the gain of? Or are you trying to determine the overall amplification of the entire set? You state that you have muted the oscillator and have injected the signal from the generator into the grid of the convertor. Why have you muted the oscillator? Since you are going in at signal frequency, you will only get the IF signal out of the convertor if the oscillator is running. If, OTOH, you are trying to determine the gain of the IF stage, then you won't inject the signal into the freq. convertor.

I'd like to help - but I am totally confused as to what your objective is and the method you are using to achieve it; sorry.

Al. [Skywave]

G8HQP Dave · 17th Jan 2011, 8:02 pm

Let's try to make some sense of what the OP said. Assume 100mV=0dB. Then -40dB is 1mV. If the 0-10 control is at 6 then this might mean 0.6mV output - this probably assumes the correct loading (75ohms?) so the actual voltage could be up to 1.2mV.

50mW probably means 50mW output to speaker. However, you could calculate the corresponding anode voltage. The gain from your injection point to the anode is then
V anode/ 0.6mV (or 1.2mV). If V anode is 16V, then gain is 26667 (or down to 13333).

Of course, this is not the receiver gain as you have disabled the LO. It is not the IF gain as you have injected at the converter grid. Why disable the LO?

gezza123 · 17th Jan 2011, 8:38 pm

HI: Guy's sorry for any confusion .the (0 to 10) give the no. of microvolts fro 0 to 10
Sorry I meant in milliwatts .Acording to the book I am tring to measure the full stage gain of the reciever.

It says that the 50milliwatts is the standard for most recievers witch equates to 16vols on the meter,I seem to get what it states but am confused about the markings on the Taylor 67a .my other taylor seems straight forward as it is measured in x1 to x10.000 multiplier and microvolts from 0 to 10.

What I do is set the reciever up and get the output to give me 16volts and then I check the generator atenuators and multiply the numbers IE:Example TAYLOR 65b set to x1000x6 this gives me 6000 microvolts.according to the calculation you have to divide the microvolts by 50 millivolts.so you can keep the output of 16volts while you progress through the various stages.
But going from the converter gives me the gain of the whole radio.please bear with me.Gezza sorry guy's can't upload the book.

G8HQP Dave · 17th Jan 2011, 8:45 pm

You still seem to be confusing milliwatts (power) and millivolts (voltage). You need to be clear about this. Otherwise you have no hope of measuring anything. I don't understand your calculation. Have you correctly understood the book you refer to?

The gain from the converter grid to the output anode is meaningless if the LO is disabled. The real receiver gain, with LO working and injection at signal frequency instead of IF, will typically be 4-6 times less.

gezza123 · 17th Jan 2011, 9:25 pm

hi guy's I think daves on the right track but still confused.
trying to load info,don't know if you got it.gezza

Station X · 17th Jan 2011, 9:45 pm

Quote:

50Mw.or 16volts ac on the meter

You need to forget this and look for a power level of 50mW (50 milliwatts) at the loud speaker, the speaker being in circuit.

As you're actually measuring voltage across the speaker you'll need to calculate the power from the voltage. This is given by Volts x Volts/R or Volts times Volts divided by R. So if you have a 5 ohm speaker and see 5 Volts across it the power is 5 watts. I'll leave you to work out what voltage represents 50mW (fifty thousandths of a Watt) in your speaker.

The RF output level will be the sum of the settings of the attenuator control (marked in dB) and the power level control marked 1 to 10. I don't know what units the power control uses, but 100s of millivolts would be a good guess to start with.

gezza123 · 17th Jan 2011, 10:50 pm

Thank guy's here is the file.I am beginning to wonder if I should have bothered.

I think all I should have asked for was how to read the dials on this generator.

all good fun.Gezza

Skywave · 17th Jan 2011, 10:57 pm

Quote:

Originally Posted by gezza123

Acording to the book I am tring to measure the full stage gain of the reciever.

Let's get one basic fact quite clear before you go any further. A 'receiver' can be analyzed into a number of logical stages, each one performing a specific function. You can measure the 'stage gain' of each of these stages, but to say I am "measuring the full stage gain of the reciever" is a meaningless phrase. You are either measuring the gain of a particular stage or you are measuring the total gain of the entire receiver.

Others here might have some idea, but I still do not understand what it is that you are trying to do.

Al.

MichaelR · 18th Jan 2011, 12:00 am

Gezza,

Are you trying to make the measurements as described in the posted attachments.

These seem to be IF stage gain measurements.

Mike

AlanBeckett · 18th Jan 2011, 12:37 am

How about a diagram.
A scanned sketch would be fine.
Alan

G8HQP Dave · 18th Jan 2011, 12:29 pm

I think much of the confusion originates from whoever wrote that generator setup text. My advice is to ignore it. Now, what are you actually trying to do?

Station X · 18th Jan 2011, 12:43 pm

I would start with something simple like measuring a receiver's overall sensitivity.

Just inject a signal at the aerial socket and, with volume at maximum, measure the AF output (mW) for a given RF input (uV).

gezza123 · 18th Jan 2011, 4:18 pm

hi:guy's in my first post I may have mislead you,if so so sorry.
I think what I realy wanted was,how to interpretate the reading on the signal generator.Taylor 67a
IE: if I set to -60 dB + No. 6 on the generator what would be the output of the generator signal,to do the tests I am looking at in the book.
I thought it might be a good excersise as there is no data available for my radio CR-66.

gezza123 · 18th Jan 2011, 4:22 pm

hi: thanks Graham.that is what I am really trying to do,but don't understand the output of the generator.gezza

Station X · 18th Jan 2011, 5:01 pm

Neither do I. Is it possible you could scope the generator's output and monitor the voltage as you vary the controls? Remember you'll have to multiply the peak to peak value by 0.707 and then divide by two to get the RMS value. Then depending on whether the output is potential difference (pd) or electro motive force (emf) you may need to divide by two again.

geofy · 18th Jan 2011, 5:10 pm

Quote:

Originally Posted by gezza123

hi:guy's in my first post I may have mislead you,if so so sorry.
I think what I realy wanted was,how to interpretate the reading on the signal generator.Taylor 67a
IE: if I set to -60 dB + No. 6 on the generator what would be the output of the generator signal,to do the tests I am looking at in the book.
I thought it might be a good excersise as there is no data available for my radio CR-66.

Relative to 0db -60dB would be 0.000001 The dB scale is a relative measure from a reference voltage or power.

dBm indicates that the reference quantity is one milliwatt, while dBu is referenced to 0.775 volts RMS. and dBμV/m referenced to microvolts per meter for radio frequency signal strength. (Source Wikipedia)

The 50mW for 16 Volts could be just for that particular meter.

But be careful about the symbols MW = Megawatt, mW = Milliwatt

G8HQP Dave · 18th Jan 2011, 5:26 pm

We have already been told that max output is 100mV (i.e. 0dB on switch, 10 on pot?). I think that means that if you want 50mV, set 0dB and 5. For 3mV, set -20dB and 3. OK?

Ignore all the stuff about 16V and 50mW - that must assume something about the OPT ratio and the modulation depth, neither of which we know.

17th Jan 2011, 5:57 pm	#1
gezza123 Heptode Join Date: Mar 2010 Location: Eastham, Wirral, Merseyside, UK. Posts: 788	Technical question please HI,Guy's I have a Taylor 67a Signal Generator,and the dials or marked in (-dB)IE: 0 -20 -40 -60 -80 the RF output is (0 to 10).The max output seems to be 100Mv. Ive been trying to do a Stage-Gain test. The I.R.E says the standard set for stage-gain is set to 50mw.ac across the audio output transformer. So I have set up my radio and get 50Mw.or 16volts ac on the meter with the controls set up and the oscillator muted,and the signal is fed into the grid of the converter so am I correct in my working results. The generator is set for -40dB and the RF is set to 6. I have worked it out as 100mv-40dB = 60X10 = 600 x 6=3600uv/50Mw =72.is this about the correct gain of my radio . Thank you for your comments.Gezza

17th Jan 2011, 6:06 pm	#2
ppppenguin Retired Dormant Member Join Date: Dec 2003 Location: North London, UK. Posts: 6,168	Re: Technical question please There's a lot of confusing numbers here. What's all the megawatts and megavolts for? I'll assume you mean milliwatts (mW) and millivolts (mV). How on earth does 16V correspond to 50mW at the output? That would only be true if the impedance is over 5kΩ. Are you by chance measuring at the primary of the output transformer perhaps? In which case do you know the ratio of said transformer so that you can calculate the impedance at the primary? Other questions. What is the AGC up to? Have you disabled it? Is there any overloading? There shouldn't be at 50mW but it's nice to know for certain. The actual output level is not important if you are measuring gain, provided that there is no overloading and you are aware of what the AGC is up to.

17th Jan 2011, 7:10 pm	#4
Skywave Rest in Peace Join Date: Jun 2006 Location: Chard, South Somerset, UK. Posts: 7,457	Re: Technical question please I really cannot understand just what it is that you are trying to measure. You refer to 'Stage gain'. Which particular stage in this radio are you trying to determine the gain of? Or are you trying to determine the overall amplification of the entire set? You state that you have muted the oscillator and have injected the signal from the generator into the grid of the convertor. Why have you muted the oscillator? Since you are going in at signal frequency, you will only get the IF signal out of the convertor if the oscillator is running. If, OTOH, you are trying to determine the gain of the IF stage, then you won't inject the signal into the freq. convertor. I'd like to help - but I am totally confused as to what your objective is and the method you are using to achieve it; sorry. Al. [Skywave]

17th Jan 2011, 8:02 pm	#5
G8HQP Dave Rest in Peace Join Date: Sep 2008 Location: Solihull, West Midlands, UK. Posts: 4,872	Re: Technical question please Let's try to make some sense of what the OP said. Assume 100mV=0dB. Then -40dB is 1mV. If the 0-10 control is at 6 then this might mean 0.6mV output - this probably assumes the correct loading (75ohms?) so the actual voltage could be up to 1.2mV. 50mW probably means 50mW output to speaker. However, you could calculate the corresponding anode voltage. The gain from your injection point to the anode is then V anode/ 0.6mV (or 1.2mV). If V anode is 16V, then gain is 26667 (or down to 13333). Of course, this is not the receiver gain as you have disabled the LO. It is not the IF gain as you have injected at the converter grid. Why disable the LO?

17th Jan 2011, 8:38 pm	#6
gezza123 Heptode Join Date: Mar 2010 Location: Eastham, Wirral, Merseyside, UK. Posts: 788	Re: Technical question please HI: Guy's sorry for any confusion .the (0 to 10) give the no. of microvolts fro 0 to 10 Sorry I meant in milliwatts .Acording to the book I am tring to measure the full stage gain of the reciever. It says that the 50milliwatts is the standard for most recievers witch equates to 16vols on the meter,I seem to get what it states but am confused about the markings on the Taylor 67a .my other taylor seems straight forward as it is measured in x1 to x10.000 multiplier and microvolts from 0 to 10. What I do is set the reciever up and get the output to give me 16volts and then I check the generator atenuators and multiply the numbers IE:Example TAYLOR 65b set to x1000x6 this gives me 6000 microvolts.according to the calculation you have to divide the microvolts by 50 millivolts.so you can keep the output of 16volts while you progress through the various stages. But going from the converter gives me the gain of the whole radio.please bear with me.Gezza sorry guy's can't upload the book. Attached Thumbnails

17th Jan 2011, 8:45 pm	#7
G8HQP Dave Rest in Peace Join Date: Sep 2008 Location: Solihull, West Midlands, UK. Posts: 4,872	Re: Technical question please You still seem to be confusing milliwatts (power) and millivolts (voltage). You need to be clear about this. Otherwise you have no hope of measuring anything. I don't understand your calculation. Have you correctly understood the book you refer to? The gain from the converter grid to the output anode is meaningless if the LO is disabled. The real receiver gain, with LO working and injection at signal frequency instead of IF, will typically be 4-6 times less.

18th Jan 2011, 12:00 am	#12
MichaelR Retired Dormant Member Join Date: Mar 2006 Location: Sheffield, South Yorkshire, UK. Posts: 1,587	Re: Technical question please Gezza, Are you trying to make the measurements as described in the posted attachments. These seem to be IF stage gain measurements. Mike

18th Jan 2011, 12:37 am	#13
AlanBeckett Rest in Peace Join Date: Dec 2008 Location: Burton upon Trent, East Staffordshire, UK. Posts: 1,686	Re: Technical question please How about a diagram. A scanned sketch would be fine. Alan

18th Jan 2011, 12:29 pm	#14
G8HQP Dave Rest in Peace Join Date: Sep 2008 Location: Solihull, West Midlands, UK. Posts: 4,872	Re: Technical question please I think much of the confusion originates from whoever wrote that generator setup text. My advice is to ignore it. Now, what are you actually trying to do?

18th Jan 2011, 12:43 pm	#15
Station X Moderator Join Date: Jan 2003 Location: Ipswich, Suffolk, IP4, UK. Posts: 21,288	Re: Technical question please I would start with something simple like measuring a receiver's overall sensitivity. Just inject a signal at the aerial socket and, with volume at maximum, measure the AF output (mW) for a given RF input (uV). __________________ Graham. Forum Moderator Reach for your meter before you reach for your soldering iron.

18th Jan 2011, 4:18 pm	#16
gezza123 Heptode Join Date: Mar 2010 Location: Eastham, Wirral, Merseyside, UK. Posts: 788	Re: Technical question please hi:guy's in my first post I may have mislead you,if so so sorry. I think what I realy wanted was,how to interpretate the reading on the signal generator.Taylor 67a IE: if I set to -60 dB + No. 6 on the generator what would be the output of the generator signal,to do the tests I am looking at in the book. I thought it might be a good excersise as there is no data available for my radio CR-66.

18th Jan 2011, 4:22 pm	#17
gezza123 Heptode Join Date: Mar 2010 Location: Eastham, Wirral, Merseyside, UK. Posts: 788	Re: Technical question please hi: thanks Graham.that is what I am really trying to do,but don't understand the output of the generator.gezza

18th Jan 2011, 5:01 pm	#18
Station X Moderator Join Date: Jan 2003 Location: Ipswich, Suffolk, IP4, UK. Posts: 21,288	Re: Technical question please Neither do I. Is it possible you could scope the generator's output and monitor the voltage as you vary the controls? Remember you'll have to multiply the peak to peak value by 0.707 and then divide by two to get the RMS value. Then depending on whether the output is potential difference (pd) or electro motive force (emf) you may need to divide by two again. __________________ Graham. Forum Moderator Reach for your meter before you reach for your soldering iron.

18th Jan 2011, 5:26 pm	#20
G8HQP Dave Rest in Peace Join Date: Sep 2008 Location: Solihull, West Midlands, UK. Posts: 4,872	Re: Technical question please We have already been told that max output is 100mV (i.e. 0dB on switch, 10 on pot?). I think that means that if you want 50mV, set 0dB and 5. For 3mV, set -20dB and 3. OK? Ignore all the stuff about 16V and 50mW - that must assume something about the OPT ratio and the modulation depth, neither of which we know.