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Synthesized Tx’s what’s available how do they work?

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Old 08-20-2005, 11:13 AM
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SDR-Hammer
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Default Synthesized Tx’s what’s available how do they work?

I’m sure all the information I need is available for the taking here on RCU but I’m on a very slow dial up so I’m hoping all the right info will be placed in my lap by you guys.

I’m gathering some info for the newsletter regarding frequency control and I would like to know who is producing synthesized Tx’s and how the frequency changes are accomplished? Is it dials on a module, programming through the Transmitters computer, etc? Also I need to know how the modeler confirms what Channel the Tx is broadcasting on. Does is come up on a screen or is pulling the module to look at the settings necessary?

I’m not shopping or making comparisons between units so I don’t need opinions… Just the facts.

Thanks.
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Old 08-20-2005, 05:10 PM
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Default RE: Synthesized Tx’s what’s available how do they work?

The only one that I am involved with is the JR PLL Module. The principle of operation is fairly simple, on the rear of the module are 2 decade switches. These are read on switch on by a microprocessor and outputs clock and data to a variable phase comparator. The data stream tells the comparator what division ratio to set itself to. Another input to this comparator is a 13 MHz crystal, this is divided down internally and becomes the reference signal.

The last input to this IC is a sample from the RF Oscillator. This oscillator is controlled by a varactor diode which is biased by the output of the comparator. As the oscillator starts up, the sample is divided down ( ratio as set by the data stream from the microprocessor ) and is compared against the reference frequency. If the phase is different then the output from the comparator will adjust the biasing on the varactor diode which in turn adjusts the oscillator frequency.

Meanwhile, the DC power to the RF Amplifier is switched off via a simple CR timer. The timer allows sufficient time for the RF Oscillator to settle before powering up the RF Amps.

Should an incorrect channel be assigned via the 2 switches, the microprocessor detects this and prevents the RF Oscillator and Amplifiers from powering up.

The Data stream from the micro is only sent on power up, therefore if the switches are moved during transmission, nothing will happen and the module continues to transmit on its initial channel.

The actual RF frequency generated by the oscillator is ( in the case of the 72MHz variant ) at about 18 MHz. The RF Amps will double this freq, filter, double again, filter then amplify prior to being fed to the Antenna stage.

I may be slightly incorrect on that last part, I am not 100% certain on how many times it is doubled.




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Old 08-20-2005, 05:20 PM
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Default RE: Synthesized Tx’s what’s available how do they work?

The Polk TX uses programming to change the channel. The channel is stored with the model # memory.
When turning it on the sceen displays both frequency and channel number while the built-in scanner checks to make sure that channel is not busy. If the channel is being used the radio beeps and displays a bar meter showing the strength of the signal/interferance.
If the channel is clear it then starts to transmit and the screen displays the model # and the channel number.
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Old 08-20-2005, 05:24 PM
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Default RE: Synthesized Tx’s what’s available how do they work?

Airtronics
http://www2.towerhobbies.com/cgi-bin...?&I=LXGRF3&P=7 dials on the module

Futaba 9C
http://www2.towerhobbies.com/cgi-bin...?&I=LXHKB1&P=7 dials on the module
Futaba 9Z
http://www2.towerhobbies.com/cgi-bin...?&I=LXH278&P=V ?

Hitec
http://www2.towerhobbies.com/cgi-bin...?&I=LXN550&P=7 dials on the module

Polk Hobby
Tracker III 50 channel synethsized with built in scanner prevents shoot downs.
Manual - http://www.polkshobby.com/pdf/2005_0...ker3manual.pdf
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Old 08-20-2005, 06:46 PM
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Default RE: Synthesized Tx’s what’s available how do they work?

It might also be good to discuss the power requirements for a synth module compared to a xtal module in your article. In the case of 9C synth module, it is 20% more.
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Old 08-20-2005, 08:19 PM
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Default RE: Synthesized Tx’s what’s available how do they work?

Re the JR PLL module. I will measure that on Monday.
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Old 08-21-2005, 02:04 PM
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Default RE: Synthesized Tx’s what’s available how do they work?


ORIGINAL: Mac_Man_UK

Re the JR PLL module. I will measure that on Monday.
and when did they bring out the 35mhz one for the uk ?

i what one if they have .
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Old 08-21-2005, 05:17 PM
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Default RE: Synthesized Tx’s what’s available how do they work?

The latest batch of 9XII's are shipping with the PLL modules. Hopefully the module will be available shortly (mid Sept at a guess )



I have had a preproduction sample for some time.... Helps working for MacGregor... LOL
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Old 08-21-2005, 10:39 PM
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Default RE: Synthesized Tx’s what’s available how do they work?

Mac_Man_UK

Does the JR Synth module do both PPM and PCM where you just select either in the software like on the 378 or is there a seperate one for each like for the 3810.

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Old 08-22-2005, 02:05 PM
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Default RE: Synthesized Tx’s what’s available how do they work?

The TS35-J ( Synth RF Module ) is like any of the modern JR modules. It only contains the RF Oscillator and RF Amplifiers. The data input is dependant on the TX and so it will take both PPM and PCM.

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Old 08-22-2005, 08:00 PM
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Default RE: Synthesized Tx’s what’s available how do they work?

Now that is what I wanted to here. The new 9X V2 hasn't had much released about it here in Oz. All the stores keep listing the V1 information. Well, now that I know it will do both time for me to go order one, woahoo. This should be a nice step up from the 631.
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Old 08-23-2005, 02:47 AM
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Default RE: Synthesized Tx’s what’s available how do they work?

Multiplex Royal Evos have the option of a synth module, frequency is selected in software and requires a re-boot of the tx to enable the change in order to prevent someone just hopping frequency by accident. Channel check is also used to prevent the tx from transmitting if it detects anyone else on that frequency. When switching on the tx it always shows the channel number and asks you to confirm that you do want to transmit on that channel by pressing the enter button, it won't transmit until you have confirmed the channel and it has done its channel check.

Synths are also available for the Multiplex Profis but these are on European 35Mhz and are unlikely to be made for 72Mhz.

H
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Old 08-23-2005, 05:10 PM
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Default RE: Synthesized Tx’s what’s available how do they work?

Further to my last, the current difference between the standard JR RF Module and the new Synthesised RF Module is about 20 mA. The Synth module drew an extra 20mA. However, that was on a sample of 1. I will have to wait until I can grab a slack handful and measure then all to get an average.



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