Re: DC-508 repair advice


Hi Pete,
I can answer your questions about what the Option 7 is for:
It is used with a TR-502 tracking generator and a TM-503 which has wired interconnections between these two plugins on the TM503 backplane. This DC508/TR502/TM503 combination will then connect to the 7L13 or 7L14 Spectrum Analyzers through a special 6 wire cable with LEMO connectors on each end to measure the exact frequency the 7L13 or 7L14 is tuned to and display it on the DC508 counter. As the spectrum analyzer's trace sweeps across the CRT, it stops momentarily at the midpoint of the CRT long enough for the DC508 to measure the frequency of the TR502 and display it with up to 1Hz precision. Once the DC508 makes the measurement it releases the sweep of the 7L13 or 7L14 to continue. The entire pause only lasts as long as the measurement period of the DC508 which can be anywhere from 1mS to 1S depending on how much resolution you want. The DC508 is capable of measurements up to 1.3GHz although these two SAs go up to 1.8GHz.

I think you are correct about connecting the TR502 Aux Out to the DC508. It's been a while since I used all of this and I am not certain.

It is a very clever combination of several instruments (tracking generator, spectrum analyzer, and frequency counter) making a very difficult and useful measurement if you are working with RF.

Dennis Tillman W7PF

-----Original Message-----
From: radioconnection@...
Sent: Sunday, December 08, 2019 6:29 AM
Subject: [TekScopes] DC-508 repair advice

Hello to the group--not exactly a Scope problem, but I was given a TM-503 that was full of plug ins. There is a 508 counter that does have the preselector daughter board installed.

It is not working. When using the presecaler the input level led shows it is seeing a signal from my HP-8640 signal generator. The gate lamp is flashing. The display leds are blanked until the counter sees a signal, and then the LEDs only show zeros, but no counts. On the direct input the counter also does not count. Gate lamp is flashing. The PLL light goes out when I apply a 1 kHz signal. I am guessing there is something wrong with the gate since the input and timebase seem to be working?

I do not have extender boards and I am very unfamiliar with this counter. I did download a PDF file of the manual, but it is rather cumbersome to use on a computer. Any suggestions where to start?

Also, I've read there is an Option 7 that was intended to use the DC508 with a TR-503? What exactly does that show? The center scan or the exact count as the SA is being swept? The 503 does have an aux. RF out that could be fed to the DC-508, will that do the same function?


Dennis Tillman W7PF
TekScopes Moderator

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