[TenTec] CorsairII sidetone modification

[Mike Bryce]

I wonder if an adjustable coil could be found that would allow one to change and peak the sidetone freq as needed. 


While the pitch control still works, the L-C components are locked. 

Mike wb8vge 

Sent from my iPhone

On Mar 15, 2013, at 4:57 PM, "Jerry Haigwood" <jerry at w5jh.net> wrote:

> Steve,
>    I hope you leave the pictures on the web site until I get around to
> building it.
> Jerry W5JH
> "building something without experimenting is just solder practice"
> 
> 
> 
> 
> -----Original Message-----
> From: TenTec [mailto:tentec-bounces at contesting.com] On Behalf Of Steve Hunt
> Sent: Friday, March 15, 2013 3:37 PM
> To: Discussion of Ten-Tec Equipment
> Subject: [TenTec] CorsairII sidetone modification
> 
> I finally decided I needed to do something about the "raspy" sidetone on my
> CorsairII. Being a lazy guy I was looking for a simple and easy modification
> that made a significant improvement with minimal alterations to the radio.
> This is what I came up with - not sure if it's original?
> 
> Audio waveform before the modification:
> http://www.karinya.net/g3txq/corsair_sidetone/before.jpg
> 
> Audio waveform after the modification:
> http://www.karinya.net/g3txq/corsair_sidetone/after.jpg
> 
> I simply added two components to form a high-Q tuned circuit across the
> Sidetone Level control. Here's the schematic:
> http://www.karinya.net/g3txq/corsair_sidetone/schematic.png
> 
> Lmod and Cmod are the two new components - they resonate at 650Hz.
> 
> This was the implementation:
> 
> I took a small piece of PCB material and scored a gap along the centre - one
> side for ground and one side for the connection to R96,R97,C65. I bent a
> solder tag and soldered it to the ground side of the board:
> http://www.karinya.net/g3txq/corsair_sidetone/board.jpg
> 
> I wound 122 turns of ecw on a high permeability toroid (I got tired at that
> stage) and measured the inductance as 40mH. I calculated I would need 1.5uF
> for resonance at 650Hz. Mounted the toroid on the board with a hot glue gun,
> and soldered a 1uF and a 0.47uF capacitor in parallel:
> http://www.karinya.net/g3txq/corsair_sidetone/circuit.jpg
> 
> Then mounted the board at the front of the IF/AF board using the existing
> mounting screw between the AF Gain and Notch controls. 
> Connected a short lead (yellow lead in the photo) between the board and the
> exposed end of R96; the board gets its ground through the mounting
> screw:
> http://www.karinya.net/g3txq/corsair_sidetone/installation.jpg
> 
> Adjustment simply consists of adjusting the sidetone pitch to place it at
> the centre of the new filter - it peaks noticeably as you adjust it.
> 
> Result: much nicer sounding sidetone; minimal changes to the radio; Sidetone
> Pitch and Level controls still work as normal.
> 
> If you decide to replicate the mod, be aware that the inductor needs to be
> pretty high Q otherwise the output level drops considerably - I measured the
> Q of mine as 330. Initially I tried one of the small Toko inductors, but its
> Q was less than 10!
> 
> The inductance is not critical - I tried values of 20mH to 100mH when I was
> experimenting - simply choose the matching capacitance value to resonate at
> your preferred sidetone frequency.
> 
> Hope that may be of interest to some. In slower time I'll write it up as a
> page on my web site.
> 
> 73,
> Steve G3TXQ
> 
> 
> 
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