Crt hercule pll woes

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Edd200sx
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Crt hercule pll woes

Post by Edd200sx »

Read this thread
http://transmission1.net/viewtopic.php?t=54717

I can get readings from the points suggested but I can’t tune to 10.240 only 10.23984/10.23934

I’ve changed some caps and tried a different 10.240 crystal

Bit stuck
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cb4ever104
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Re: Crt hercule pll woes

Post by cb4ever104 »

What exactly is the problem? If your 10.240 reference is 600hz off , that won't stop the radio from working .
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Edd200sx
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Re: Crt hercule pll woes

Post by Edd200sx »

Usually get them closer I wasn’t sure if there was a problem
lbcomms
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Re: Crt hercule pll woes

Post by lbcomms »

Two possibilities, you could be either loading the oscillator with your counter and causing a false low reading, or actually have a slightly low frequency there.

The 10.240 signal is used to synthesize the channel spacing (10.240 divided by 1024 = 10 KHz) so it can be indirectly measured (i.e. without connecting anything directly to the oscillator itself) by measuring the channel spacing.

Put it on AM channel 1, and set the the radio frequency to exactly 26.965.000, then change to channel 40 and measure again.
If it's slightly higher than 27.405.000 you were loading it and getting a false low reading. If it's slightly lower than 27.405.000 then 10.24 oscillator is actually lower.

Being only a few hundred hertz off, the frequency error on channel 40 might be insignificant and not worth the bother to correct it.
There is a 100pF cap connected to the crystal, reducing it to 82pF or 68pF will bring the frequency up a tad - but if you go too low the crystal may stop oscillating altogether...
Edd200sx
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Re: Crt hercule pll woes

Post by Edd200sx »

Many thanks bud makes sense. Yes the radio is working ok as is
I can see why nick hates rangers now 😂
lbcomms wrote: 23 Feb 2019, 14:30 Two possibilities, you could be either loading the oscillator with your counter and causing a false low reading, or actually have a slightly low frequency there.

The 10.240 signal is used to synthesize the channel spacing (10.240 divided by 1024 = 10 KHz) so it can be indirectly measured (i.e. without connecting anything directly to the oscillator itself) by measuring the channel spacing.

Put it on AM channel 1, and set the the radio frequency to exactly 26.965.000, then change to channel 40 and measure again.
If it's slightly higher than 27.405.000 you were loading it and getting a false low reading. If it's slightly lower than 27.405.000 then 10.24 oscillator is actually lower.

Being only a few hundred hertz off, the frequency error on channel 40 might be insignificant and not worth the bother to correct it.
There is a 100pF cap connected to the crystal, reducing it to 82pF or 68pF will bring the frequency up a tad - but if you go too low the crystal may stop oscillating altogether...
satelitesid
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Re: Crt hercule pll woes

Post by satelitesid »

Plus it all depends on how accurate the counter is, if it is calibrated, when it was calbrated, and the sampling frequency.
160 Hz is nothing to worry about anyroad
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