[TenTec] Omni VI & SignaLink USB

[Bob McGraw - K4TAX]

My reference to input and output impedances and to transformers on the input 
and output are from Tigertronics

As provided with the SignaLink USB  data sheet.

I  quote;
"Radio In/Out Z:	600 Ohm (nom).  TX/RX Levels are fully adjustable for
			compatibility with Hi-Z and Low-Z radio connections."

>From SignaLink USB data sheet I quote:
"Unlike some interfaces on the market, ALL SignaLink models COMPLETELY 
isolate your computer from your radio.  This eliminates troublesome ground 
loops and prevents hum and noise from degrading the signals.  The SignaLink 
USB provides isolation through the use of audio transformers and a 
relay-based PTT keying circuit."



73
Bob, K4TAX




----- Original Message ----- 
From: "Jim Brown" <k9yc at audiosystemsgroup.com>
To: <tentec at contesting.com>
Sent: Thursday, July 10, 2014 12:18 PM
Subject: Re: [TenTec] Omni VI & SignaLink USB


> On 7/10/2014 6:41 AM, Bob McGraw - K4TAX wrote:
>> Tigertronics i.e. SignaLink has transformers on the input and output 
>> signals for isolation.
>
> A transformer does NOT provide isolation to differential mode signals. It 
> only blocks common mode signals. For example, audio voltage on both 
> windings of a 1:1 transformer are equal, and no impedance is added to the 
> differential circuit. In a 4:1 transformer, the voltages are proportional 
> to the turns ratio, and the impedance looking into the transformer is 
> equal to terminating Z multiplied by the square of the turns ratio.
>
> Remember that "600 ohms" has not been used in pro audio for at least 40 
> years. Output stages are low-Z sources, typically 100 ohms for pro 
> products, 300 ohms or more for consumer stuff, and input stages are high 
> impedance, typically 10K for pro products, 50K for consumer products. The 
> impedance of a microphone is defined as 1/5 of it's recommended minimum 
> load impedance, and a low-Z mic's output Z is typically on the order of 
> 100 ohms. All commonly used ham mics are low-Z, wired unbalanced.
>
> As you have described the schematic, with individual 10K in series with 
> both the mic and line inputs, I agree there should be good isolation. 
> Perhaps the schematic is not accurate?
>
> 73, Jim K9YC
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