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Doubling a reference frequency
GM Folks,
My 10Mhz TCXO that I use for a frequency counter timebase has gone toes up and I only have a 5Mhz one available to replace it. Can anyone offer ideas to double the 5 Mhz TCXO keeping the M:S ratio accurate enough for use with the frequency counter ?. The 5Mhz TCXO has an output of 2v P-P sinewave into 50R and I need TTL level 50:50 M:S at 10Mhz. Thanks, Mike W |
"Mike W" wrote in message
... GM Folks, My 10Mhz TCXO that I use for a frequency counter timebase has gone toes up and I only have a 5Mhz one available to replace it. Can anyone offer ideas to double the 5 Mhz TCXO keeping the M:S ratio accurate enough for use with the frequency counter ?. The 5Mhz TCXO has an output of 2v P-P sinewave into 50R and I need TTL level 50:50 M:S at 10Mhz. You could use a diode doubler with a tuned 10 MHz amplifier. 73, Leon |
Check your counter specs. Some will take 1, 5 or 10 mhz time base without doing anything. 73 Gary K4FMX On Fri, 27 Aug 2004 07:32:37 GMT, (Mike W) wrote: GM Folks, My 10Mhz TCXO that I use for a frequency counter timebase has gone toes up and I only have a 5Mhz one available to replace it. Can anyone offer ideas to double the 5 Mhz TCXO keeping the M:S ratio accurate enough for use with the frequency counter ?. The 5Mhz TCXO has an output of 2v P-P sinewave into 50R and I need TTL level 50:50 M:S at 10Mhz. Thanks, Mike W |
Gary Schafer ) writes: Check your counter specs. Some will take 1, 5 or 10 mhz time base without doing anything. 73 Gary K4FMX That's a good point. Given that they will all divide the timebase down to a very low frequency, even if there's nothing specific one could likely tap higher up on the divider chain. Michael VE2BVW On Fri, 27 Aug 2004 07:32:37 GMT, (Mike W) wrote: GM Folks, My 10Mhz TCXO that I use for a frequency counter timebase has gone toes up and I only have a 5Mhz one available to replace it. Can anyone offer ideas to double the 5 Mhz TCXO keeping the M:S ratio accurate enough for use with the frequency counter ?. The 5Mhz TCXO has an output of 2v P-P sinewave into 50R and I need TTL level 50:50 M:S at 10Mhz. Thanks, Mike W |
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My 10Mhz TCXO that I use for a frequency counter timebase has gone toes up and I only have a 5Mhz one available to replace it. Can anyone offer ideas to double the 5 Mhz TCXO keeping the M:S ratio accurate enough for use with the frequency counter ?. Feed the 5 MHz to both inputs of a high level DBM. The output will be sum and difference, kill the DC component with a 0.1 uF coupling cap and you probably can use the 10 MHz result. If not, a little low pass filter to get rid of the higher frequency responses will make it useable. W4ZCB |
A few turns on a teeny ferrite ring 1:2 transformer, centre-tapped
secondary, and a couple of diodes will double the frequency without any power loss. |
Thankyou everyone for your responses.
I eventually dived into the counters divider chain and found there was a div2 just where I needed it, so I'm back to "nearly on frequency". All I have to do now is verify the accuracy of the 5Mhz TCXO :-) atb Mike W |
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In message , Reg Edwards
writes A few turns on a teeny ferrite ring 1:2 transformer, centre-tapped secondary, and a couple of diodes will double the frequency without any power loss. What Reg is describing here is undoubtedly the BEST and EASIEST and MOST PREDICTABLE way to double the frequency of a signal. You can also use it to obtain x2 and x6 etc, but with reducing efficiency. I have frequently used it to get signals up to about 1000MHz. It s exactly the came circuit as for a bi-phase rectifier on a mains power supply, ie transformer with centre-tapped secondary and two diodes. The shape of the output waveform is the same as what you get from the rectifier circuit, ie a series of half sinewaves (all +ve or -ve, depending on which way you connect the diodes). This contains an infinite series of even harmonics and no odds (including the fundamental). For the mathematical, the theoretical level of each harmonic can be predicted from a knowledge of what Mr Fourier says about this shape of waveform (from the coefficients associated with each frequency). See below for several examples (just click on the examples at the bottom of the page). http://www.efunda.com/math/fourier_s...ier_series.cfm In theory, there are no losses. But you are splitting a single signal into a load of even harmonics, so the level of each must be less than the original signal. In practice, there ARE losses (in the diodes and the ferrite). From memory, the x2 is about 8dB down, x4 is about 16dB down, x6 is about 24dB on the original signal. These ratios are essentially independent of drive level, provided you have sufficient to overcome the knee of the diodes. If you are after the x4 and x6, you can actually do things which reduce the loss somewhat, and make the multiplication more efficient. But I digress... Finally, a big advantage of this circuit is that the odd harmonics are well suppressed. They are not zero, but are typically 30 - 40dB less than the adjacent evens (depending on the balance of the circuit). This makes any filtering (if the application requires it) SO much easier. Cheers, Ian. -- |
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