[ARC5] Bandwidth for IF Transformers

[Mike Feher]

I see what you mean. It appears the meaning of selectivity has changed over
the years. In fact, now it is typically referred to as the xdB bandwidth
which includes both sides from center. Thanks for the clarification. 73 -
Mike  

 

Mike B. Feher, N4FS

89 Arnold Blvd.

Howell, NJ, 07731

732-886-5960 

 

From: ARC5 [mailto:arc5-bounces at mailman.qth.net] On Behalf Of Kenneth G.
Gordon
Sent: Wednesday, March 16, 2016 11:02 PM
To: Mike Feher
Cc: ARC-5 List
Subject: Re: [ARC5] Bandwidth for IF Transformers

 

On 16 Mar 2016 at 22:42, Mike Feher wrote:

 

> Ken -

> 

> I have not looked at the manual, so do not know if they show a selectivity

> curve, but, from the table you listed I would expect that those numbers
are the

> total bandwindth nad not half. 73 - Mike 

 

OK, Mike, perhaps you would care to interpret this quotation from the Navy
AN/ARC-5 maintenance manual, AN 16-30ARC5-2, table 6.4 on page 47...

 

"   The SELECTIVITY, expressed in kilocycles, is defined as the displacement
of the carrier frequency from the resonant frequency, required to produce
standard output, when the radio frequency voltage input is twice (2X), ten
times (10X), one hundred times (100X), and one thousand times (1000X) that
required to produce standard output at resonance. Standard output for these
measurements should be 1 volt across 300 ohms in order to keep the level low
enough not to be affected by the AVC. The resonant sensitivity should be
reduced to 50 microvolts by the manual RF sensitivity control in order to
keep the output noise voltage low. The radio frequency voltage input to the
receiver must be modulated 30% at 400 cycles for both the resonant and
off-resonant measurements. The selectivity values shown below are those
resulting from an average of the selectivity measurements made on either
side of resonance."

 

Notice it says, "...EITHER side of resonance." and not, "...BOTH sides of
resonance."

 

Over to you...

 

Oh. And by the way, the Army manual says substantially the same thing: that
the measurement is from center to ONE SIDE of the IF passband, not both.

 

If you would like me to, I will also quote that one to you for you to
interpret as you see fit.

 

Ken W7EKB

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