Digital modes on an older radio

Discussion in 'Working Different Modes' started by KN4HTC, Aug 6, 2019.

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  1. KN4HTC

    KN4HTC XML Subscriber QRZ Page

    Pardon me if this has already been asked.

    I have a TenTec Omni D.

    I would like to try out some of the digital modes and just wonder if it would even be possible to use it for that. I know that I would not have the ability to have the computer control the radio but would it be possible to interface the computer and radio audio, set the radio on VOX (and be sure to turn any and all notifications off), and manually tune the radio?

    I know it's obviously its not the ideal setup. Just wondering if it's theoretically possible to do so. If so, I'll pick up some 1/4-3.5 cables and give it a shot.

    If anyone has tried this successfully, any recommendations on what settings work best?

    Thanks in advance.
  2. KC9YGN

    KC9YGN Platinum Subscriber Platinum Subscriber QRZ Page

    Sure you can. All you need is to route the audio from your rig (headphone or speaker) into your computer's sound card, and your computer's sound output into the mic input of your rig. Just be cautious about audio levels so you don't overdrive your transmitter and get a distorted signal. As long as your transceiver doesn't drift in frequency you shouldn't have a problem.
    KN4HTC likes this.
  3. KS2G

    KS2G Subscriber QRZ Page

    Get on the Air with HF Digital (2nd Edition)
    Now Including Popular Modes FT8 and WSPR!
    $19.95 plus shipping

    Instructions for radio interfacing and older radio are in Chapter 1.

    KN4HTC likes this.
  4. KN4HTC

    KN4HTC XML Subscriber QRZ Page

    Now that I think about it I guess that was kind of a duh question. I mean how did we use digital modes before the advent of computer controlled radios. Ha.

    KA0HCP likes this.
  5. K7TRF

    K7TRF Premium Subscriber QRZ Page

    Yeah, it's not only theoretically possible but many hams go this route. I've run digital modes on a number of older rigs including my TS-830s, TS-130S and yeah a Ten Tec Omni C and they all worked fine. A couple of thoughts:

    - It's best to use some form of transformer or optically isolated interface between your rig and your PC sound card to eliminate ground loops and AC hum on your transmissions and reception. You can build something but commercially available devices like a Signalink USB make that really easy, these show up on the used market all the time:

    - Watch your transmit audio and mic gain level carefully as you don't want to see ANY ALC action on the meter while transmitting

    - Manually tuning the rig is a non issue, just think of that tuning of the VFO as a coarse tuning that gets you to some digital activity of interest but the fine tuning is done on the PC in software where you pick a specific digital signal off the waterfall display to work. You don't tune the main rig much once you've got it to a frequency where you see several compatible digital signals in your waterfall display.

    - Frequency drift in the older rigs is the big issue, the TT Omni series is pretty good where drift is concerned but it can pay to let your rig warm up a while before trying to operate digital modes. You'll know it if your rig drifts excessively as all the received digital streams in your waterfall display will drift and skew across the screeen as diagonal instead of vertical lines.
    KK4NSF and KN4HTC like this.
  6. KK4NSF

    KK4NSF Ham Member QRZ Page

    I use a TS-440s for digital modes, and it works very well. The trick is to make sure your levels are set correctly, which is a big P-I-A.... unles you use a digital interface, like the SignaLink. (listen to K7TRF!) That makes it go from clunky to easy.
    KN4HTC likes this.
  7. KA0HCP

    KA0HCP XML Subscriber QRZ Page

    As you said, we did digital modes before CAT or computer control.

    -Many of the digital programs, SSTV programs and older PSK programs include help files with schematics and instructions for interface/keying devices you can build for about $10 if you don't have junk box parts. You can find many through a google search as well.
    **It is crucial to have good electro isolation between the radio and computer to prevent RFI.**

    -I strongly recommend avoiding using Mic Input and VOX keying. It's less reliable, slower, and simply inelegant. Key the PTT line directly, and input your Audio directly into the Accessory port (if available). This will generally avoid internal filters that distort the digital signal.

    Jump in! bill
    KN4HTC likes this.

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