HT1000 VCO Crossover setting
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I was always wondering about the VCO crosover point setting. I do not remember ever seeing any information on it. Is it in the manual for the RSS? If you have further information on that adjustment, please post it, I am courious. I have one HT1000 UHF 403-470 that will not receive, it will unsquelch when the monitor button is pressed and the "squelch" noise sounds normal. The radio transmitts fine.
Hi Will, sorry I didn't get back to you regarding the VCO crossover setting. The holidays kept me busy.
The crossover adjustment is mentioned on page 15 of the jedi service manual.
If I may quote the manual "Note - This procedure is only required after field repair of a VHF or UHF VCO"
I have found after servicing many of these radios, that the VCO setting is often modified by people who don't know that this is something that shouldn't be touched and is set at a fixed value for a particular bandsplit. Also, when modding a radio with lab, or dumping an improper codeplug, the VCO crossover frequency is changed and the radio is no longer capable of tuning to the entire wide band (1 band in VHF, and 2 in UHF).
Essentially, like all softpots do, is that the VCO crossover softpot changes the voltage in the circuit. So in order for a PLL to tune to wide bands, large swings in both positive and negative voltages are required. The VCO crossover sets the point or frequency at which the voltage at the VCO is zero. The VCO is then free to swing to positive and negative voltages as dictated by the controller which supplies the frequency. So when you drop the crossover as in the case of the person with the HT1000 earlier this week, the radio becomes deaf to high frequencies (even withing the radio's rated bandsplit).
For example, in an RDC HT1000
403------------------470
X X=factory set crossover
403------------------470
X X= low crossver setting so the radio will not "hear or speak" on frequencies on the upper edge of the bandsplit.
Try raising the RX VCO crossover on your radio a bit and see if that solves the problem. The fact that you hear static confuses me a bit since you shouldn't if the radio can't synthesize a frequency. Give it a try and let me know. Hope this was helpful.
Chris
The crossover adjustment is mentioned on page 15 of the jedi service manual.
If I may quote the manual "Note - This procedure is only required after field repair of a VHF or UHF VCO"
I have found after servicing many of these radios, that the VCO setting is often modified by people who don't know that this is something that shouldn't be touched and is set at a fixed value for a particular bandsplit. Also, when modding a radio with lab, or dumping an improper codeplug, the VCO crossover frequency is changed and the radio is no longer capable of tuning to the entire wide band (1 band in VHF, and 2 in UHF).
Essentially, like all softpots do, is that the VCO crossover softpot changes the voltage in the circuit. So in order for a PLL to tune to wide bands, large swings in both positive and negative voltages are required. The VCO crossover sets the point or frequency at which the voltage at the VCO is zero. The VCO is then free to swing to positive and negative voltages as dictated by the controller which supplies the frequency. So when you drop the crossover as in the case of the person with the HT1000 earlier this week, the radio becomes deaf to high frequencies (even withing the radio's rated bandsplit).
For example, in an RDC HT1000
403------------------470
X X=factory set crossover
403------------------470
X X= low crossver setting so the radio will not "hear or speak" on frequencies on the upper edge of the bandsplit.
Try raising the RX VCO crossover on your radio a bit and see if that solves the problem. The fact that you hear static confuses me a bit since you shouldn't if the radio can't synthesize a frequency. Give it a try and let me know. Hope this was helpful.
Chris
Press F3 from the service menu, F5 to select receive vco crossover softpot. (the screen will indicate the rx. test freq. to be used) Connect a dc voltmeter capable of 1mVolt resolution to test point 5 (TP5) which is accessible through a hole in the bottom side VCO circuitry shield. Beginning with the default softpot frequency of line 2, adjust the Up/Down arrow keys until the voltage reading at TP5 is 3.0+/-0.1 volts Press F8 to program the softpot value Press F10 twice to get to the service menue.
Sounds like your synthesizer circuit is working fine enough. If you're not receiving on any frequency, I don't believe your problem has anything to do with the VCO crossover. I have replaced the 73.55MHz filter in the IF section a few times, not much else to try unless you have the proper equipment for shield removal.On 2001-12-26 17:12, Will wrote:
I was always wondering about the VCO crosover point setting. I do not remember ever seeing any information on it. Is it in the manual for the RSS? If you have further information on that adjustment, please post it, I am courious. I have one HT1000 UHF 403-470 that will not receive, it will unsquelch when the monitor button is pressed and the "squelch" noise sounds normal. The radio transmitts fine.
Todd
I will check to see if the VCO is running at the correct frequency, and measure the voltage at the test point. The receiver "squelch" noise sounds normal, usally the noise is degraded to much less if a componet in the IF is bad, like the crystal filter.
If the radio is programmed to 461 mhz receive what would be the VCO frequency?
Would it be 461 mhz minus 73.55MHz?
Unfortunatey I do not have a manual for this radio any more.
If the radio is programmed to 461 mhz receive what would be the VCO frequency?
Would it be 461 mhz minus 73.55MHz?
Unfortunatey I do not have a manual for this radio any more.