Alinco DR-235 Repeater

Discussion in 'General Technical Questions and Answers' started by WB2HKK, Dec 7, 2018.

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  1. WB2HKK

    WB2HKK Ham Member QRZ Page

    I am using an Alinco DR-235 as a transmitter for an AllStar 220 repeater. The audio input is via the rear DB-9 connector pin 3 ( 9600 baud, no preemphasis ). The PL is injected along with the tx audio from a URI. I have to increase the PL level quite high to get it to where it decodes, then the audio gets raspy. Looking at the service monitor, the PL sine wave is not clean. Anyone have experience with this??
     
  2. K7JEM

    K7JEM Ham Member QRZ Page

    How are you mixing the two audios together to inject them at that point? What PL encoder are you using?
     
  3. WB2HKK

    WB2HKK Ham Member QRZ Page

    Using AllStar DSP software, the TX audio is created digitally by the software, along with the PL, and fed to the URI digitally, where it is converted to analog and fed to the transmitter. The ' mixing ' is done digitally in the software. Our 2M Motorola CDM radio has no problem with this. I looked into the Alinco schematic, and see that the 9600 Baud input does feed directly to the modulator, so I'm perplexed as to why it has a problem. I see no filters or pre-emphasis that would affect the audio bandwidth.
     
  4. K7JEM

    K7JEM Ham Member QRZ Page

    The first thing I would do would be to try inserting just a low frequency tone into the DR235, and see if it will modulate the tone correctly. There could be an issue with using that input port to insert low frequencies, since it is designed for packet. Some FM radios do not modulate low frequency tones correctly, on most modern radios the PL tone is also fed to the reference oscillator to give a lower distortion. That doesn't appear to be happening with the Alinco, it just runs to the varactor in the modulator. Depending on the PLL loop frequency components, the PLL itself could be trying to correct.

    In fact, looking at the DR235 schematic, the PL and DPL are not supplied to the normal modulator, they are only applied to the reference oscillator crystal. This allows them to modulate essentially down to DC, which is needed for proper DPL encoding.

    So, my guess is that the back connector will not properly support PL injection, without severe distortion. If you could separate the PL from the URI audio, you could probably run it directly to the same point on the circuit where Alinco is injecting their PL.

    Is there a problem using the internal PL generator? Does it not work when in packet mode?
     
    KK5JY likes this.
  5. K9STH

    K9STH Platinum Subscriber Volunteer Moderator Platinum Subscriber QRZ Page

    Virtually all FM / PM transmitters limit the lower end of audio to around 300 Hz. That is, frequencies below 300 Hz are "rolled off". As such, when a CTCSS ("PL" is Motorola's registered trademark for CTCSS) tone is inserted with the normal audio, it takes a considerably higher level for that low frequency tone to modulate the carrier. This higher level, unfortunately, will distort the actual desired modulation.

    That is why the CTCSS tone is usually added after the desired audio has reached the desired level for modulating the carrier. When an external CTCSS generator is used, a convenient place for the insertion is the wiper of the deviation control. At this point, a much lower CTCSS level is required and the desired audio is not distorted by the CTCSS tone.

    Glen, K9STH
     
  6. WB2HKK

    WB2HKK Ham Member QRZ Page

    Thank you all for your thoughts...they are inline with my own. The suggestion to use the Alinco's own tone generator is exactly what I was thinking. We do not need to change the CTCSS frequency remotely, so it will not prove to be a problem. Of course, it WILL require another trip to the Watchung Mountains site...ugggg!
     
  7. K7JEM

    K7JEM Ham Member QRZ Page

    You might make sure the Alinco PL encode will work when radio is in packet mode.
     
  8. WB2HKK

    WB2HKK Ham Member QRZ Page

    Your right, the encode is disabled in packet mode.
     

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