[MRCA] T-195B and volts

[Ray Fantini]

Cool test! I am surprised to see that much variation in the frequency. Just in case there are one or two people out there who don't know how the auto tune system works let me try to describe it. The discriminator or auto tune system uses a bridge that senses if a load out of resonance with the source. It can determine this in both induction and capacity and in the process produce a proportional negative or positive DC voltage being at zero volts when everything is matched. The auto tune function works with chopper, amplifier and two phase AC synchro motor. The incoming AC source is fed to one side of the synchro motors windings as a reference signal. The output DC voltage of the discriminator is feed to the chopper with the chopper operating in phase with the reference winding of the synchro. The output of the chopper will produce an AC voltage that's leading or lagging in phase to the reference voltage depending on if it's negative or positive. If the discriminator is in balance, the load matches the source there is no voltage produced. The small AC signal that's produced by the chopper is amplified and feed to the second winding of the synchro motor and depending on the relationship of the two phases that determines the direction that the motor turns. If the system is in balance there is no voltage on the second winding and the motor stops. When it works it's a thing of beauty have watched this endlessly in the ARC-38 and 180L automatic antenna tuners. As far as the choppers not functioning it is important to remember that just because the vibrate that has no guarantee that they are any good. Three or four years ago I went thru a whole bunch before finding a couple good ones. Looking at the internal design can see where building a solid state replacement would not be out of hand using something like a CD-4066 switch being that has good bidirectional response and very low internal resistance. If anyone thinks this is interesting maybe next I can go on about how Collins devised a set of restive networks to do the course setting of the servo systems during band change!

Ray F

-----Original Message-----
From: mrca-bounces at mailman.qth.net [mailto:mrca-bounces at mailman.qth.net] On Behalf Of B. Smith
Sent: Tuesday, September 29, 2015 1:25 PM
To: mrca at mailman.qth.net
Subject: Re: [MRCA] T-195B and volts

I was curious and measured the 400 cycle output  frequency of one of my  
T-195 low voltage dynamotors.
On my set:
22 volts =405 cycles
26 volts= 430 cycles
30 volts= 455 cycles

Z




On 9/28/2015 5:08 PM, Ray Fantini wrote:
> AC synchronous choppers, the hart of auto tune discriminators are very frequency sensitive. What may be happening is not an issue of voltage but of frequency. The solid state replacement inverters in the later models may produce a more tolerant 400 cycle source for the choppers then the old dynamotors and perhaps the old dynamotor versions tended to change frequency beyond the tolerance range of the choppers due to poor regulation or sag when keying the transmitter. Remember that frequency of the output of the dynamotor is directly proportional to the speed of the motor itself.
> Radios like the ARC-38 and the 180L automatic antenna tuners use the choppers and they were tolerant of working only with in about 20 cycles above or below 400 cycles, I am assuming the 400 cycle source in the T-195 is one of the dynamotors and not a solid state inverter.
>
> Ray F
>
> -----Original Message-----
> From: mrca-bounces at mailman.qth.net [mailto:mrca-bounces at mailman.qth.net] On Behalf Of B. Smith
> Sent: Monday, September 28, 2015 3:33 PM
> To: grasshopper; mrca at mailman.qth.net
> Subject: Re: [MRCA] T-195B and volts
>
> First things first, I would look at all power supplies especially the
> 400 cycle system, check servo power supply input and output voltage and look at the 400 cycle wave form , maybe the 400 cycle wave form is getting chopped up at lower voltages. But don't expect a nice sine wave but look for it to be consistent in frequency etc.
> Z
>

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