[TenTec] Omni VI & SignaLink USB

[Bob McGraw - K4TAX]

G M to all.

In the case of the Omni VI radio there is no provision to select either the 
front  MIC input or the rear AUDIO IN input.  These are isolated via each 
other using a 10K resistor to each input but are both active inputs all of 
the time.  Thus both the SignaLink and mike are connected to the mike 
amplifier at a summing point inside the radio.   What we found is noise 
being introduced into the audio when both are connected and the mike is 
being used.   Further we found that this did not happen when the SignaLink 
was ON but no data being generated but noise did occur when the SignaLink 
was OFF.

Once I realized what was happening it was clearly understandable.  There is 
an opamp that drives the SignaLink output transformer which feeds audio to 
the radio.  When the SignaLink is ON the source impedance or output 
impedance of the opamp is very low thus the circuit, cables, transformer and 
such is properly terminated as a low source impedance.  When the SignaLink 
is OFF the audio stage floats to a very high Z and the associated circuit 
acts more like a random piece and length of wire connected to the AUDIO IN 
on the Omni VI.  Thus noise is induced.

The solution was then very clear and simple.  Just keep the SignaLink USB 
powered at all times.  Or disconnect the AUDIO IN cable from the back of the 
radio. In the specific installation, that is not the easiest thing to do due 
to the physical layout of the station.

Thanks to all for your excellent suggestions.

We live and learn every day.

73
Bob, K4TAX


----- Original Message ----- 
From: "Al Sirois" <alsirois at roadrunner.com>
To: "Discussion of Ten-Tec Equipment" <tentec at contesting.com>
Sent: Friday, July 11, 2014 4:09 AM
Subject: Re: [TenTec] Omni VI & SignaLink USB


> 0500 EDT
> Friday
> 11 July 14
>
> G.M., Bob:
>
> Although I had some difficulty making the correct setting when getting 
> started, things are working well, NOW.
>
> As instructed in the MENU, I normally select "both" MIC & AUDIO ACCESSORY 
> when doing MARS.
>
> We utilize MT-63-2K most of the time. I don't disconnect the MIC at any 
> time. The MIC can be disconnected thru the MENU.
>
> N1MHC at arrl.net
> Al Sirois
> East Boothbay, ME
> ===============
>
> -----Original Message----- 
> From: Bob McGraw - K4TAX
> Sent: Thursday, July 10, 2014 8:45 AM
> To: Discussion of Ten-Tec Equipment
> Subject: [TenTec] Omni VI & SignaLink USB
>
> I'm trying to assist a friend setting up his Omni VI with a SignaLink USB. 
> He does have the cable supplied from SignaLink and it seems to be 
> connected to the radio correctly.  It receives and decodes PSK-31 very 
> satisfactorily and it keys the transmitter correctly.
>
> The difficulty is having both the SignaLink connected to the Audio IN on 
> the rear and the microphone connected to the front at the same time.  The 
> SignaLink appears to key the radio correctly but does not produce output. 
> When he then later and on a different frequency tries to transmit SSB only 
> white noise is heard.  If he unplugs the cable to/from the SignaLink the 
> noise is not heard. This occurs when the SignaLink is off or on.
>
> It appears from the schematic the mike input on the front and the rear 
> Audio In are each isolated by a 10K series resistor to a summing point at 
> the mike amp input.  Using a low impedance {500 ohm} dynamic mike and the 
> SignaLink output being some 600 ohms, I calculate the isolation between 
> the two inputs would be some 35 dB or so. Certainly this would seem to be 
> very adequate isolation such that having the two connected, although the 
> SignaLink is off, it would not interfere with the use of the mike.  And 
> with the SignaLink on it would produce audio and it would not be 
> interfered with the connected mike.
>
> Anyone have any specific experience or thoughts on this configuration?
>
> 73
> Bob, K4TAX
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