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Old 01-21-2017, 06:16 PM
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Zenith6S321 Zenith6S321 is offline
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Join Date: Aug 2010
Location: Charleston, West Virginia
Posts: 303
The first picture is the spectrum of the B&K 415 RF output from about 38 to 49 MHz. Its varies about 3 dbV.

The second picture shows the downconverter output with a 20MHz sine wave to shift the 45.75 MHz sweep down to 25.75 MHz (45.75 - 20 = 25.75). Other harmonics show up, but the TV IF only amplifies its IF range signals (19.75-27.25 for this case). This downconverted output also varies by about 3 dbV.

If your old TV has a different IF range you calculate the value to enter into the sine wave generator by taking the 45.75 - your_TV_video_carrier_frequency = sine_wave_frequency. In the case of this TS721 its 45.75 - 25.75 = 20MHz.

The third picture shows the display of the B&K 415 scope XY outputs with the downconverter RF connected to an RCA 721TS tuner converter sweep input test point and with a direct probe (a scope probe set to 1X) connected to the video detector sweep test point. Yes, the B&K 415 markers all work since they are added by the B&K after the signal comes from the TV and the B&K then drives the scope H&V inputs.

The scope I am using is my new Digilent Analog Discovery USB scope. It's limited to a 50 MHz bandwidth, but it includes a bunch of features like a spectrum analyzer (FFT), a logic analyzer, an I2C and SPI serial protocol analyzer and a lot more. Here is a link if you are in the market:
http://www.digikey.com/en/product-hi...FRGBswodfAoO-Q
Be sure to get the BNC adapter as it expands the input frequency range when using scope probes instead of the fly-leads:
http://www.digikey.com/product-detai...073-ND/4840860
I thinks it's a great value for $280.

The fourth picture is the IF spectrum input to the video detector. It makes it easy to get the traps tuned to exactly 21.25MHz.
Attached Images
File Type: png B&K415-Output-Spectrum.png (78.7 KB, 37 views)
File Type: png B&K415-20MHz-Mixer.png (71.2 KB, 29 views)
File Type: png B&K415-721TS-Sweep.png (86.7 KB, 32 views)
File Type: png B&K415-Output-Spectrum-721TS-DetectorIn-2.png (66.6 KB, 30 views)

Last edited by Zenith6S321; 01-21-2017 at 06:23 PM.
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