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10mhz does not equal any standard audio sampling rate. So does your player accept 10mhz? If so it must have an internal PLL with a divider chain to lock to 10mhz. And that PLL chain will probably have more jitter than a simple CXO at the proper frequency. Also a BNC tee is a poor way to split an RF signal. Just as paralleling two 8 ohm speakers makes a 4 ohm load, two 50ohm loads in parallel is 25ohms, so much for maintaining proper cable impedance. Also the signal will be at half the launch amplitude. At a minimum you need a 1x2 pad to maintain the impedance on both loads. But ths will still cause a 3db drop in signal level. If you can't tolerate that, than a distribution amplifier is needed. If you want to distribute video or RF and don't want losses via pads or resort to an active distribution amplifier - here's the trick.
You need to do a "loop through" topology. This was very common with analog video systems. Also 50ohm Ethernet "Thinnet" worked the same way. If your devices have two BNC connectors wired in series for the external clock input, then you are set to loop through. If not, some modification will be required. Remove the 75ohm termination resistor on both device's clock inputs. Then put a BNC Tee right at the 1st device connector. If it's an RCA jack, it's ok to use a BNC to RCA adapter, the impedance mismatch at this short distance is insignificant at 10mhz. Then run a RG58 cable from the clock generator to the first BNC Tee. Then another cable to the second device with another BNC Tee attached. Then pout a 50ohm terminator on the end of the last BNC. This will maintain the proper cable impedance as well as the proper signal level. You can repeat this loop for as many as 10 devices and over 100 feet of cable at 10mhz. Note this assumes your clock source is 50ohms as is most likely the case with an atomic standard. If however it's 75ohms, just use 75ohm cable, RG59 or RG6, and terminate with a 75ohm terminator resistor rather than 50 ohms.
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