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 Post subject: How do I connect my equipment to sweep align?
PostPosted: Mar Sun 16, 2014 3:25 am 
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Location: Monte Vista, Colorado
Hi

I don't want to sound dumb or anything but I have a question. I have a HP 3325a generator and a Tek 465m scope. I'm trying to figure out how to connect the two in order to do a sweep alignment on a Sangean 818 radio. The service manual calls for sweep alignment of the AM and FM IF. I've done alignments before but not a sweep alignment. I know enough to know you have to run the scope in X-Y mode and that you connect the signal generator to the radio but how do you connect the sweep up to the scope? There isn't a sweep output on the 3325a that I can see. Please bear with me, this is my first attempt at doing a sweep alignment. I want to learn how to do this and am willing to spend the time to get it right.

Thanks

Chris


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 Post subject: Re: How do I connect my equipment to sweep align?
PostPosted: Mar Sun 16, 2014 3:36 am 
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Chris, look on the rear panel. Should be a ramp output if it is similar to the 3336 generators.

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 Post subject: Re: How do I connect my equipment to sweep align?
PostPosted: Mar Sun 16, 2014 3:48 am 
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Location: Chillicothe, Ohio 45601
I hope someone post a detailed example because I need to figure out how to do it with my HP3324A. I know the actual sweep comes out of the RF to the radio. Probe (or RF prob) goes from radio to vertical on the scope. Where I get confused is do I hook sync out on the generator to channel B or external trigger on the scope or do I just use the marker out on the generator to the Z input on the back of the scope? Or maybe both?

I would really love to see a video of someone aligning an old tube radio with these modern HP sweep generators.

Rod

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 Post subject: Re: How do I connect my equipment to sweep align?
PostPosted: Mar Sun 16, 2014 4:09 am 
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I'll try asking once more. :mrgreen:

Is there is 0 to 10 volt X output BNC jack on your rear panels????

If so, that is connected to the X input on your scope. That is Channel 1 on a 465. Channel should should be set for 1 volt per division, and DC coupling!

Once you have the X channel being driven by the generator X output the discussion can progress to using the vertical Y channel to observe the signal.

Pete

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 Post subject: Re: How do I connect my equipment to sweep align?
PostPosted: Mar Sun 16, 2014 4:21 am 
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Hi Pete

There is an X drive output on the rear of the generator. I'll hook that to channel 1 and set it up per your instructions. I assume I will be hooking my probe up to the Y input and then to the radio?

Chris


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 Post subject: Re: How do I connect my equipment to sweep align?
PostPosted: Mar Sun 16, 2014 4:27 am 
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Vertical input goes to the radio... but how it is used depends on what you are looking at.

A FM discriminator output will be a DC level. That goes directly to the vertical scope input, DC coupled. This allows you to center the discriminator on the 0 crossing line, and to get a feel for the detector's linearity.

If you are monitoring an IF stage, there are several options. For example Bogen uses the limiter voltage on their FM IF strips for the vertical input to set the IF alignment,. You don't need a special diode detector probe when aligning a Bogen.

You can also use a diode detector to monitor the IF signal directly. It will convert the IF signal into a DC level to drive the scope. There is more than one way to use the vertical input so it gets confusing.

Pete

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 Post subject: Re: How do I connect my equipment to sweep align?
PostPosted: Mar Sun 16, 2014 4:31 am 
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yes I have an X drive on the back

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 Post subject: Re: How do I connect my equipment to sweep align?
PostPosted: Mar Sun 16, 2014 4:41 am 
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Repeat of a post from last month:

This is how I set up either the HP 3325A or 8662A for sweeping, the 3336C is virtually the same thing.

1) Set oscilloscope to X-Y mode
2) Connect sweep ramp output from signal generator to scope horizontal axis (on 3325A it is on back panel, called X drive)
3) Connect RF demodulator probe to scope vertical axis (Mike uses a log detector circuit here, useful to see signal down to noise floor and you can use a standard oscilloscope probe.)
4) Set sweep up on signal generator for desired start frequency and end frequency, and desired sweep time. Set sweep start and end at an even frequency from the IF frequency you wish to sweep; say if you are sweeping 455 kHz, you might use 425 kHz for start, and 485 kHz for end. This gives a 60 kHz total sweep with 455 kHz in the middle. Don't forget to actually turn the sweep on so you can see it!
5) Set scope horizontal to capture and center the sweep in a set number of divisions (I typically use 8, so in above example each scope division represents 7.5 kHz, or 60 divided by 8 )
6) Connect signal generator RF output to device under test, and set output amplitude accordingly
7) Connect RF probe to device under test. Set scope vertical input to capture swept signal at desired amplitude
8) Optional- you can connect the Z axis marker output of signal generator to the scope Z axis blanking input and set a marker within the sweep. I usually use this as extra insurance.

-Mark-

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 Post subject: Re: How do I connect my equipment to sweep align?
PostPosted: Mar Sun 16, 2014 6:20 am 
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Location: Chillicothe, Ohio 45601
Ok here was my attempt at a quick setup. It was with a junk radio chassis just an unpowered 455khz transformer. Am I getting close?

Image


Edit: Played some more and now I got what I was expecting. I think I got it.

Image


Thanks,
Rod

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 Post subject: Re: How do I connect my equipment to sweep align?
PostPosted: Mar Sun 16, 2014 2:24 pm 
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Based on the pic it looks like you've got it, but do your scope a favor and move the vertical retrace bar, and start dot off the screen to the left, or at least off of the phosphor.

A couple hours of "playing" with it, and you'll find the whole process opens up lots of possibilities.

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 Post subject: Re: How do I connect my equipment to sweep align?
PostPosted: Mar Sun 16, 2014 4:01 pm 
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Bottom trace is it!

Now, you can connect the Z output from the generator to the Z input on the scope, and it will give you a marker indicator, but you shouldn't need it.

Be careful not to use too fast of a sweep setting in the generator or it may distort the swept waveform. It is pretty evident when you start reaching the limit.

Pete

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 Post subject: Re: How do I connect my equipment to sweep align?
PostPosted: Mar Sun 16, 2014 6:17 pm 
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Are you using any kind of special probe to get that trace or are you using a standard scope probe?


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 Post subject: Re: How do I connect my equipment to sweep align?
PostPosted: Mar Sun 16, 2014 6:50 pm 
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For an AM set you can monitor the detector diode. Or, use an RF probe. The RF probe may have enough stray capacity to detune some IF transformers.

I usually use the detector, but I always short the AGC bus after the AGC filter to keep the AGC from distorting the response curve. Mike uses a log detector, which is neat to have once you gain more experience.

You can use a scope probe, but it will show the RF envelope. It isn't as pretty, but it will show the same outline on a sweep.

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 Post subject: Re: How do I connect my equipment to sweep align?
PostPosted: Mar Sun 16, 2014 8:16 pm 
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ck81144 wrote:
Are you using any kind of special probe to get that trace or are you using a standard scope probe?


I'm using a BK PR32A RF prob http://www.mouser.com/ProductDetail/BK- ... MgodbA4AQg If you search the forums there are plans to make your own prob but since I'm new at sweep alignment I wanted to take the possibility of a bad prob out of the equation.

Rod

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 Post subject: Re: How do I connect my equipment to sweep align?
PostPosted: Mar Mon 17, 2014 1:43 am 
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Thank you. I will get one of those probes and experiment. Is it possible to just hook up an IF transformer on the bench to get that waveform or do I actually need to hook up to a radio?


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 Post subject: Re: How do I connect my equipment to sweep align?
PostPosted: Mar Mon 17, 2014 2:58 am 
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Location: Chillicothe, Ohio 45601
I just did mine with an IF transformer. Of course you really can't align one for a radio that way because the circuit will change the alignment but it is good to get the equipment down.

I touched up the alignment on an old clock radio today that I already had done the peak method. The hardest part was figured out where measure the output at since this radio didn't have sweep instructions but being an AA5 it didn't take long to figure it out. If your Sangean 818 has the sweep instructions you should be good to go once you get your equipment setup down.

And thanks to Pete, Mark and Mike for all the help. I'm not sure how long it would have taking me to figure out that I needed to use the X drive on the back.

Rod

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Last edited by hotrod on Mar Mon 17, 2014 12:14 pm, edited 1 time in total.

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 Post subject: Re: How do I connect my equipment to sweep align?
PostPosted: Mar Mon 17, 2014 3:41 am 
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hotrod wrote:

I would really love to see a video of someone aligning an old tube radio with these modern HP sweep generators.

Rod


Here one where I align a Philco 60MB with a HP3336A and Tek 465 scope. : http://youtu.be/0hTmpKmPTdA


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 Post subject: Re: How do I connect my equipment to sweep align?
PostPosted: Mar Mon 17, 2014 4:08 am 
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ck81144 wrote:
Thank you. I will get one of those probes and experiment. Is it possible to just hook up an IF transformer on the bench to get that waveform or do I actually need to hook up to a radio?



The low Z output impedance of the generator will load the IF transformer. If you just want to experiment you can use a small capacitor, say around 10 pF, between the generator output and the IF transformer. That will give you a decent impedance match.

Just connect the detector probe to the secondary winding directly.

Pete

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 Post subject: Re: How do I connect my equipment to sweep align?
PostPosted: Mar Mon 17, 2014 4:54 am 
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bandersen wrote:
hotrod wrote:

I would really love to see a video of someone aligning an old tube radio with these modern HP sweep generators.

Rod


Here one where I align a Philco 60MB with a HP3336A and Tek 465 scope. : http://youtu.be/0hTmpKmPTdA

While watching THAT video I saw your speaker repair video too:
... And ..here's another source for speaker cones such as those you buy from Mat electronics:
http://www.electronix.com/advanced_sear ... =1&x=0&y=0

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 Post subject: Re: How do I connect my equipment to sweep align?
PostPosted: Mar Tue 18, 2014 1:56 am 
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Location: Chillicothe, Ohio 45601
bandersen wrote:
hotrod wrote:

I would really love to see a video of someone aligning an old tube radio with these modern HP sweep generators.

Rod


Here one where I align a Philco 60MB with a HP3336A and Tek 465 scope. : http://youtu.be/0hTmpKmPTdA



Thanks for the link. I ran into the same problem you had with your first scope with the Z blanking everything else. Don't really need the marker with such an accurate generator though.

Rod

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