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Re: [TenTec] Triton IV vs the Argonaut V

To: Discussion of Ten-Tec Equipment <tentec@contesting.com>
Subject: Re: [TenTec] Triton IV vs the Argonaut V
From: Ken Brown <ken.d.brown@hawaiiantel.net>
Reply-to: ken.d.brown@hawaiiantel.net,Discussion of Ten-Tec Equipment <tentec@contesting.com>
Date: Sat, 13 Oct 2007 10:27:43 -1000
List-post: <mailto:tentec@contesting.com>
Hi Mike,

Well, there are many possible explanations (at least as many 
explanations as there are circuit stages between the antenna port and 
the audio output) for one rig to be noisier than the other.

Is it really noisier though? Suppose that both rigs have identical gains 
and noise figures in all stages and that they have identical number of 
stages and identical mixing schemes. (Yes, I know this is probably not 
the case for the rigs you are comparing. I am using this "thought 
experiment" to explain how one rig might "seem to be" noisier when they 
are the same.) Now suppose that the AGC action in the two rigs is 
markedly different. While the maximum total gain from RF input to audio 
output of the two rigs is identical, when there is  very low signal 
input and the AGC is not yet controlling the gain, AND at a specific 
signal level input (such as 50 uV) they may also have identical S meter 
readings, and even identical gains, at some intermediate input signal 
level one rig's AGC may be reducing it's gain more than the other. The 
one with the higher gain at that intermediate input signal level will 
seem noisier.

With the AGC operating it is really hard to know how noisy the rig 
really is.

With the AGC defeated, you could put your 50 uV signal into each rig, 
turn the RF gains up to maximum and adjust the audio gains for equal 
measured audio output levels.  Now you have the rigs adjusted for equal 
total system gains (roughly, assuming that at this signal level the 
receiver noise is insignificant) Now remove, or reduce to a real low 
level, the input signal. The receiver with the higher measured audio 
output level is the noisier receiver.

With the AGC operating you don't really know exactly what is going on.

DE N6KB
> Now, using the same antenna.
>
> The noise level on the Argonaut V was running between S-5 and S-9
>
> On the trition, very little S-meter movement was seen and it was just  
> not that noisy
>
> so I decided to test the receiver's sensitivity with the HP signal  
> generator. I injected the signal in place of the antennas
>
> At 50uV I got S-9 on both rigs. At 1uV I could detect the signal. At . 
> 5uV I could still hear the signal from the generator. Although the  
> triton had a harder time hearing at that level.
>
> Applying the attn on the Argonaut V, reduces the noise level, but as  
> suspected reduces the signal strength  of in coming signals, too
>
> So bottom line? Why is the Argonaut V so much noisier than the old  
> Triton?
>
>
>
>   

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