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Author Topic: FT-920 and Signalink  (Read 3835 times)
N8EUI
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Posts: 146




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« on: April 11, 2012, 04:24:09 PM »

Hello to all,

I recently setup my Signalink USB to my Yaesu FT-920.  Everything is working, however, at what positions should I set my mic and rf levels on the '920?  Does it matter as long as my ALC is not deflecting or is there something else I'm missing here?

Thanks,
Tom, N8EUI
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NA4IT
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« Reply #1 on: April 11, 2012, 08:44:07 PM »

For digital operation, radio RF power output is always set to full power, mic at a normal SSB level. Use the TX control, along with the sound controls on the computer, per the SLUSB manual, to control the TX output power. A clean, effective signal can be heard with no more than 30W of power output.

ALC usually will be at a low level or not show.

Low frequency tone modes (such as those like Olivia or EasyPal) take a little more drive. Also, try to stay in the natural TX passband of your radio. Say if your radio does well from 300Hz to about 2800Hz, the stay around the middle of that (1550Hz). You will get the best results near there. At the edges, power output decreases.
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VA7CPC
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« Reply #2 on: April 11, 2012, 08:45:19 PM »

There are two philosophies:

1.  Set the FT-920 RF Power control to maximum.  If you're feeding into the FT-920 mic input, set the FT-920 "Mic Gain" so that you can generate 100 watts with the SignaLink TX Level knob turned most of the way to the right.    Then, use the SignaLink TX Level knob to control output -- limit yourself to 70 watts or so to avoid any ALC action and keep the rig linear and undistorted.

2.  Set the FT-920 RF Power control to your desired power (e.g. 20 watts).  Set the FT-920 mic gain and the SignaLink TX Level so that the ALC meter _just barely moves_, and then reduce either one of them a little bit so you have _no_ ALC.

Either way works.

I have a bias toward using the rear-panel "Data" or "Packet" or "Phone Patch" connections, rather than running through the mic preamp.  Usually, the rig's "Mic Gain" control _doesn't_ affect the gain through those rear-panel jacks.


              Charles
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N8EUI
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Posts: 146




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« Reply #3 on: April 12, 2012, 06:25:51 AM »

Thank you both for your suggestions.  I will try them and see what happens.

Thanks again,
Tom, N8EUI
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AA4PB
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« Reply #4 on: April 12, 2012, 10:53:08 AM »

Here's what I would do for the cleanest output signal:
1) Set the power control to maximum power.
2) Set the mike gain control to where you normally use it with your microphone.
3) Advance the SL transmit control until you have about 30W of RF output.

This is why you should NOT use the power control to adjust power output. Because of ripple in the passband of the radio's filters the power output can change as you move around within the waterfall. This can case the ALC to operate on some frequencies, causing poor IMD. With the power control set wide open and the audio set for 30W output, the power can go up/down a little without activating the ALC circuit. You don't have to keep riding the controls to prevent ALC. You may find 30W in some areas of the waterfall and 35W in others but it won't matter.
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N8EUI
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« Reply #5 on: May 14, 2012, 01:57:06 PM »

Hi everyone,

In response to my original question of April 11th, "I recently setup my Signalink USB to my Yaesu FT-920.  Everything is working, however, at what positions should I set my mic and rf levels on the '920?  Does it matter as long as my ALC is not deflecting or is there something else I'm missing here?"  It was suggested I set the power control to maximum power, set the mike gain control to where I normally use it for sideband and advance the Signalink transmit control until I have about 30W of RF output.

I'm a little lost here.  Why am I setting my HF rig to maximum power only to adjust the Signalink to around 30 watts?  Isn't PSK31 a high duty cycle mode?  Thus, shouldn't I be setting my rig to something lower than maximum power and then adjusting the signalink for no ALC?  I've read horror stories about finals being damaged due to operating PSK31 at high power.  Please enlighten me.

Thanks,
Tom, N8EUI



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VA7CPC
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« Reply #6 on: May 14, 2012, 05:32:02 PM »

Yes, it's a 100%-duty-cycle mode. 

You want minimum distortion in your output signal.  So you don't want ALC working at all (it has some time constants, and introduces distortion), and you don't want any power-controlling circuitry limiting the final amp's output.

So you set RF Power to 100 watts -- that's what the final amp _can_ produce.   And then you reduce the AF drive, which reduces the modulation, which reduces the RF power _actually produced_.   Everything stays perfectly linear, no distortion is introduced.

Your final amp will last forever if you only ask it to produce 30 watts and it's capable of 100 watts.

There's probably a section in the ARRL Handbook that talks about transmitter non-linearities.   This would be a good time to read it.

           Charles

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N8EUI
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Posts: 146




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« Reply #7 on: May 14, 2012, 09:10:03 PM »

Thank you Charles for the advice.  It cleared up some misconceptions I had about PSK-31.

Thanks again,
Tom, N8EUI
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