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Old 15th Jan 2021, 3:18 pm   #1
mickm3for
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Default Kenwood R2000.

Hi.

I have this R2000 with no second osc/mixer output. The circuit is a 9MHz xtal osc into a buffer stage on to a x4 frequency multiplier giving 36MHz at 0.28V p-p, coming from the emitter follower states 1.8vpp that is only .8vpp on scope (checked cal of scope) checked all parts around this circuit. The 36mhz i can not read using frequency counter if i peak the coils t1 t2 with scope on tp4 the frequency on counter is 45mhz. I removed t1 and t2 peaked them using a gdo to 36mhz still no lo2. signals out of the 2nd mixer at 9.85-9.90 are ok the 45.85-45.90 ist if into the mixer not ok , If i put a diode probe on scope and scope g1 of mixer2 i can see audio as set tuned across mw band, what have i missed Help Mick
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Old 15th Jan 2021, 4:52 pm   #2
mickm3for
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Default Re: kenwood r2000

Hi i didnt post circuit oops Mick
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Old 15th Jan 2021, 5:49 pm   #3
Station X
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Default Re: Kenwood R2000.

I hesitate to ask, but what's the bandwidth of your 'scope?
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Old 15th Jan 2021, 6:28 pm   #4
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Default Re: Kenwood R2000.

Q1 is a straight-forward fundamental mode crystal oscillator at 9MHz +/- trimmer some crystal circulating current is tapped off via C14.

Q2 is a plain old emitter follower, still at 9MHz

Q5 is running with very little bias and no emitter resistor. It will be very non-linear. `this is your frequency multiplier and the two tank circuits based around T1 and T2 are a filter to pass the 36MHz component.

Frequency multipliers like this are very touchy indeed about getting the right amount of drive amplitude. If you really only have 800mV p-p when 1.8v is expected, your 36MHz signal will drastically reduced.

Scope calibrators are usually a 1kHz squarewave and won't tell you anything about accuracy at 9MHz. To do this you need a 100MHz scope (50MHz will be rolling off a bit) AND you need a good 10:1 probe to get the bandwidth and to not capacitively load the circuit too much.

So, if your measurement gear is definitely OK, there are several possibilities. I've seen a fair few Japanese crystals go low activity and spoil amplitude or even fail to start.

Q1 or Q2 could have gone iffy, or any of the small components around them or there are circuits off leftwards beyond your snippet which could be loading the 9MHz signal.

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Old 16th Jan 2021, 1:24 pm   #5
mickm3for
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Default Re: Kenwood R2000.

Hi thanks for ideas that had crossed my mind further i still think its around mixer 2 if i place 9mhz on drain of q7,8 iget a good signal but nothing at 45mhz on the gate 1 even if i supply 36mhz from a second sg to t13 primary if the frequencys are corect this has to work am i missing something ?? i have to be.The ist local osc is said to be 45.9-75.85 converting to an if of 45.85-45.90 the local osc is correct (easc end of the tuning range) this 45mhz mixing with 36mhz osc lo2 gives 9mhz i cannot fatham even if i use an external 36mhz signal to the mixer it doesnt work. voltages are about right and i have checked the 2 mosfets. This fault developed when i selected the noise blanker but i dont see any conection as the noise blanker is after the 2nd mixer where the 9mhz is ok (sg on min signal out) Mick
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