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 Post subject: Tektronix 496 over half deaf
PostPosted: Feb Sun 04, 2018 5:51 pm 
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Joined: Jan Thu 01, 1970 1:00 am
Posts: 410
Location: Green Valley, AZ, USA
Back in Dec got one at an area hamfest, was told it worked but didn't have any power or time to check. Was told it displayed 2 meter handhelds with a paper clip for an antenna. Very nice physical shape not beat up, good crt display.
Got it home and Calibrater output ( -20dBm 100mHz) shows about 2.5 grid squares while on my signal generator set for 0.0 dBm it shows about 3.2 grid squares across its 1.8 GHz spectrum on 10dB/div and doesn't increase at 0.0dBm or +10dBm. Response flattens out 3.2 grid square. Wild guess is that the mixers might be OK since it reads the same up tp 1.8 GHz.and the fault is in the front end either attenuator or whatever it uses for an amp. The free PDFs are not easy to read, so I'll see if I can find an real original paper manual, anyone have one for sale? I'm watching eBay for a reasonable price for one.
I opened it up, like new inside, all connections seem snug. I was also told it was in storage for quite few years and wonder if there's a commonly know aging problem. Any tips or suggestions appreciated.
Thanks

Hank WD5JFR


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 Post subject: Re: Tektronix 496 over half deaf
PostPosted: Feb Mon 05, 2018 12:28 pm 
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Joined: Jun Fri 19, 2009 6:34 pm
Posts: 7949
Location: Long Island
Looks like we're not in Kansas any more. There may or may not be anything wrong with your spectrum analyzer; it's hard to tell from the information given. Unlike an oscilloscope, the vertical amplitude on a spectrum analyzer display is affected by a few different things. When you set the "reference level," it usually refers to the uppermost horizontal line on the grid. That's the highest signal level it should be displaying. The signal is read in negative numbers below that. If, for example, the reference level is set to 0 dBm and I input a -20 dBm signal, I would expect its peaks to appear two major divisions below the top. Where the baseline ends up depends on the noise level and the input attenuator setting since the instrument only has so much dynamic range and can't display levels below its own noise floor.

It should also be noted that most spectrum analyzers are capable of displaying the vertical (amplitude) axis linearly, i.e. in volts, or logarithmically in decibels. In dB mode there will be considerable compression of the amplitude display compared to linear, which is very useful when there is a big difference between the amplitude levels of the various frequencies being displayed.

By making the reference level lower, you can increase the size of the display somewhat--but be extremely cautious about doing this. The input mixer has a maximum input level which must not be exceeded or damage will occur. It's a good practice to set the input attenuator as high as possible with maximum bandwidth displayed, then work your way down to a reasonable amplitude and bandwidth for what you are trying to measure. Bear in mind that signals may contain high energy components outside the frequencies of interest, and if you only look at a narrow slice of spectrum, the out-of-band signals may be burning up your mixer and you wouldn't know it. A classic example of this is a scanner antenna near a large AM broadcast tower. You only see microvolts of signal coming in on the UHF frequencies but the mixer is getting cooked by volts of RF on the AM band.

If the display cannot be made to fill from top to bottom with any combination of settings, it is possible that you have a problem in the vertical deflection stages. It is not unusual to have a bad resistor or perhaps a bad transistor that will limit the display size. But before ripping into it and possibly causing yourself a lot of grief, the best thing to do would be to track down a copy of the operators' manual. In there you will find a check-out procedure you can use to verify that the scope is working properly (or not).

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 Post subject: Re: Tektronix 496 over half deaf
PostPosted: Feb Mon 05, 2018 4:01 pm 
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Joined: Jan Thu 01, 1970 1:00 am
Posts: 1172
Location: Tucson AZ
Sent you a private message Hank.


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 Post subject: Re: Tektronix 496 over half deaf
PostPosted: Feb Wed 07, 2018 3:41 am 
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Joined: Jan Thu 01, 1970 1:00 am
Posts: 1172
Location: Tucson AZ
Hank, did you see the private message?


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 Post subject: Re: Tektronix 496 over half deaf
PostPosted: Feb Wed 07, 2018 3:31 pm 
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Joined: Apr Fri 06, 2012 3:36 pm
Posts: 1192
Location: Erie, PA
My Tek 475 is completely deaf... I've never been able to get a word out of it since I've owned it! ;) ;)

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If I had saved all the money I've spent on test equipment, I'd probably spend it on test equipment.


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 Post subject: Re: Tektronix 496 over half deaf
PostPosted: Feb Fri 09, 2018 5:31 pm 
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Joined: Nov Wed 30, 2016 7:35 pm
Posts: 2142
Location: Sunbury, Ohio 43074
Quote:
My Tek 475 is completely deaf

Mine is too. But I could swear I heard it scream once ........

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Preserving the history of electronics, one boat anchor at a time! :)
www.bbtvtestequipment.com


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 Post subject: Re: Tektronix 496 over half deaf
PostPosted: Feb Fri 09, 2018 6:39 pm 
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Joined: Jan Thu 01, 1970 1:00 am
Posts: 1172
Location: Tucson AZ
Based on his location, assuming it's correct, I am local to him by less than 10 miles and have offered to help him try to figure out what's going on, but he apparently isn't interested in the help as I've gotten no response.


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 Post subject: Re: Tektronix 496 over half deaf
PostPosted: Feb Sun 11, 2018 11:59 pm 
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Joined: Jan Thu 01, 1970 1:00 am
Posts: 410
Location: Green Valley, AZ, USA
I sent the following text last Wednesday
Hey Bill. Thanks for the offer but I have Anritsu 2670A SA and just sold my HP 141T and plug-ins. What I need is an original manual as the online ones are not clear enough. I’m hoping I run into someone who has worked on a 496. Will keep in touch.
73
Hank WD5JFR

PS

Right now I have too many irons in the fire and the 496 is on the bottom of the list for now but I’ll get back to it it’s always on my mind


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 Post subject: Re: Tektronix 496 over half deaf
PostPosted: Feb Mon 12, 2018 12:04 am 
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Joined: Jan Thu 01, 1970 1:00 am
Posts: 1172
Location: Tucson AZ
Oh ok. I'm close by if I can help out any. Any other equipment you want to get rid of?

I assume you are a member of GVARC?


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 Post subject: Re: Tektronix 496 over half deaf
PostPosted: Feb Mon 12, 2018 12:06 am 
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Joined: Jan Thu 01, 1970 1:00 am
Posts: 1172
Location: Tucson AZ
That's weird, I never received a text or private message if that is what you mean.


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