On a Flex 6500 what is the input impedance of the 10 MHz IN (is it internally 50 ohms to gnd)

allanmryan

I'm trying to trouble shoot an external 10 MHz GPS disciplined oscillator. Measuring the unterminated RCA male I get 2.2 V P-P square(ish) wave. If there is an internal 50 ohms to ground, connecting the cable to the 6500 will cut that voltage in half and be marginal.
Thoughts?
Al Ryan
WW1RF

Mike-VA3MW

The 10Mhz input will accept a square or sine wave. The impedance is somewhere between 50 and 70 ohms if I remember correctly.

You can safely plug it in a test it. I have tried a few different 10Mhz references and they all seem to work just fine.

N5DUP

Wait a minute, I thought the 10 MHz jack on my 6400 was a 10 MHz reference OUTPUT if you have the Flex GPSDO, not an INPUT. Am I wrong?

Paul-N5DUP

KD0RC

Hi Paul, there is a 10 MHz input labelled 10 MHz In. If you have a Flex internal GPSDO installed, then you will also have a 10 MHz Out jack. If you don't have the Flex GPSDO, then the 10 MHz Out port has a metal plug in it.

DL1BB

But how do you switch to external 10MHz signal. Using the latest version of SmartSDR, the option is missing in the settings, you only have the calibration option.
73,
Dieter, DL1BB

KD0RC

Hi Dieter, you don't mention which radio you have. On my 6400 running 3.9.18, I have these options:

DL1BB

Hi Len, sorry for that. I am using the Flex-6500 with the latest SmartSDR beta version 3.9.18.

73,
Dieter, DL1BB

KD0RC

Hi Dieter, from the SmartSDR User Guide:

The 10 MHz Reference section offers a selection of 10 MHz signal sources that calibrate the local 10 MHz master oscillator. This feature is only available on the FLEX-6400/M and FLEX-6600M (not in the FLEX-6300, FLEX-6500 or FLEX-6700).

If the 6500 has a 10 MHz in jack, I think that just plugging in the 10 MHz reference signal is all that is required. If it is working, running a calibration should yield a very small number in the Offset (in ppb): field. In my case this is usually around -4 ppb (an insignificant amount).