[TenTec] Corsair II PBT Question

Barry N1EU barry.n1eu at gmail.com
Tue Oct 30 06:02:54 EDT 2012

Oops, I just realized something.  Sorry, it's early in the morning and
the brain isn't totally alive yet.

What I was REALLY seeing, was a non-flat passband.  I think it sloped
slightly downward in the treble.  The passband was actually identical
in USB/LSB - I was wrong in the previous email.  There WAS identical
sound in USB/LSB, it just wasn't flat in two out of the three
Corsairs.  That's why I suspected the product detector capacitors -
they will equally affect USB and LSB.

So I need to revise my conclusion - the Inrad filters SHOULD fix that
USB/LSB asymmetry.

Barry N1EU

On Tue, Oct 30, 2012 at 9:56 AM, Barry N1EU <barry.n1eu at gmail.com> wrote:
> I just wanted to add a note to the discussion.  I've played with 3
> Corsairs in the past couple of years.  I seem to remember that even
> after careful alignment and Inrad filter installation, two out of the
> three still had slight passband asymmetries, even after installing the
> Inrad filters.  The third Corsair was totally flat and was the only
> one that would sound the same on USB/LSB.  I tried to figure out the
> cause of the asymmetry but didn't get very far.  I suspected the
> capacitors on the output of the product detector, but never finished
> the investigation.
> Sorry to throw a monkey wrench into the discussion, but I'm not sure
> it is a 100% guarantee that the Inrad filters will cure the issue but
> they should certainly help.
> 73,
> Barry N1EU
> On Tue, Oct 30, 2012 at 9:49 AM, Barry N1EU <barry.n1eu at gmail.com> wrote:
>> http://www.inrad.net/product.php?productid=199&cat=90&page=1
>> The 756/757 will give you a symmetrical, but narrower, passband.  It
>> doesn't really make sense to go with one 2.8khz and one 2.4khz filter.
>>  Go with two filters of the same bandwidth.
>> I'd definitely go for the 2.8khz filters.
>> 73,
>> Barry N1EU
>> On Tue, Oct 30, 2012 at 9:36 AM, Daniel Schlieper
>> <daniel.schlieper at tuxomania.net> wrote:
>>> Hi Dave,
>>> I try to find the Inrad 2.8 kHz filter for 6 MHz IF, but cannot see anything
>>> suitable on the Inrad website. Do you know the order number?
>>> I wonder if this mod actually needs an 2.8 kHz filter. Would the 2.4 kHz
>>> filter (Inrad # 756) do as well? Or is the width critical?
>>> 73 Daniel DM3DA
>>> On Sat, 27 Oct 2012, David and Dianne on Comcast wrote:
>>>> Your PBT imbalance problem is likely caused by asymmetrical 2.4 KHz
>>>> filters in the Corsair II. This is a long known problem with the CSII, Omni
>>>> V and Omni VI's.
>>>> I have had similar experiences with all of the many (!) Corsair II's I
>>>> have owed over the years along with an Omni V and Omni VI. L/O and IF stage
>>>> alignments will not improve this problem caused the inconsistent performance
>>>> and design of the stock TT 2.4 KHz filters.
>>>> The remedy is to replace both 2.4 KHz stock filters with INRAD 2.8 KHz
>>>> filters in the 9 and 6 MHz IF stages and to make sure the the local ocs's
>>>> are adjusted as`perfectly as possible.
>>>> You will be rewarded with far improved SSB audio fidelity and wonderful
>>>> SSB TX audio.
>>>> What you are describing I experienced with all the TT radios of this IF
>>>> design that I have owned over the years. The 100% fix is this filter swap.
>>>> Pricey but really worth it. Any easy swap out.  You can also install the 2.4
>>>> KHz filter board (9 MHz) with sockets to make future filter swapping really
>>>> easy.  I think that Barry N1EU documented that mod. (Check out his really
>>>> neat CSII wiki site at http://corsair.wikidot.com/corsair-9mhz)
>>>> I have a last production run Omni V and last production run CSII that I
>>>> have switched out these filters and the results are super.
>>>> 73 de N1LQ-Dave
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