[TenTec] JUPITER FIRMWARE 1.17 TX Roll-off

Mon, 8 Apr 2002 20:19:17 -0500

I know I will regret this, but here goes!

For the past few years several of us around the world have been
experimenting with enhanced audio for SSB. Some folks love it. Some folks
hate it. Kinda like CW or AM I guess! HI HI. Like it or not, this has grown
rapidly in popularity, and has become a "hobby within a hobby". So much so
that, many of the newer radios are capable of handling enhanced transmit
audio right out of the box, and several studio equipment manufacturers are
targeting Hams for their products. Many of us have far more money invested
in "Rack" gear and mics than we do in our radios! Tentec is spending a great
deal of time and energy developing such capabilities for the new upcoming
Orion.

Now for the Jupiter Roll-Off explanation-----
This control will allow the user to re-position the lower edge of the
selected transmit filter. This lower edge setting affects the ENTIRE
transmitted audio range. Tentec's control range is 0 to 1270 Hz. The factory
default value is 200 Hz Low cut using the 2.55kHz filter.

When adjusting this feature it important to remember TX Bandwidth and TX
Roll-Off combine together
to determine audio quality potential. The TX Roll-Off determines where audio
starts on the lower side. The transmit filter selection determines the total
passband and the point where the audio starts to fall off on the upper side
of the frequency spectrum.
Example 1:
If you have the 2.55 kHz filter selected and set a 200 Hz TX Roll-Off, the
transmitted audio would cover the range from  200 Hz to 2750 Hz.
Total width of TX signal = 2.750 kHz.
These are Tentec's factory default settings for the Pegasus/Jupiter radios.
Connect a microphone, like a 705, Heil, or Shure 444D, and you've got
strong, solid Tentec communication quality audio. GREAT!

BUT WAIT!!!!!
Typical daily sounds usually fall between 70 Hz and 14,000 Hz, and the full
electronic reproduction of these frequencies is termed "Hi Fidelity".
Instead of 70 Hz to 14kHz,  we have only had "usable" audio frequencies
between 200 Hz and 3,000 Hz with the stock Jupiter. Up to now , that is!
Yes, I know you could beyond the 3.0 kHz TX filter all the way out to the
3.9 kHz TX filter, but that discussion is for another day and another forum.

Now, try this combination!
Example 2:
Set the Low end Roll-Off to 50hz
Select the 3.0 kHz TX Filter
Total width of TX signal =3.050 kHz
You are now covering the range of 50 HZ to 3,050 HZ.
Connect a studio quality mic, Marshall 2001, 2003, EV-RE20, etc, along with
the appropriate support equipment, and WOW!!! WHOAAAAA BABY!!!!!!!!!
Smooth balanced near "broadcast quality" audio not possible with settings in
the previous example.
Good TX audio is a function of balance occurring within the proper
parameters.
By setting the Low end Roll-Off to 50 HZ we can boost ( EQ ) the 50 Hz  to
100 Hz range to enhance the lows. This gives the audio "Balls". This is not
possible with the default settings because it doesn't pass audio frequencies
below 200 HZ.
By selecting the 3.0 kHZ filter we can boost ( EQ ) the 3.0 to 3.1 kHz range
for greater articulation of each syllable. Actually 3.1 Khz to 4.0 kHz is
optimum.
The idea here is balance, not the "all knobs to the right" syndrome that
some hams make us suffer through.
You want the ability to enhance the two fundamental ranges of 50-100 Hz and
3.0-3.1 kHz and balance the range in between. That's the reason for the user
definable TX Roll-Off.

This is not to say you'll want to use these settings all the time. You may
desire to have that extra punch that "pinched" up communication quality
audio helps to deliver while working DX pileups, and there are several
combinations of those to choose from.
That's why it is adjustable!!! Jupiter owners now have choice, and
flexibility.

As you can see from the above examples,  large TX Roll-Off with a wide
filter setting is not possible, as other factors limit the usable range.
Also, as Tentec says, the large control range will also allow digital mode
users to place narrow filters at any position they choose.

This is a feature that the Pegasus has enjoyed for some time now using
Carl's software.
I hope this helps.
Cheers and enjoy!!!
de Benton wb5twc

----- Original Message -----
From: "Joe Word" <joe_word@yahoo.com>
To: <tentec@contesting.com>
Sent: Monday, April 08, 2002 11:49 AM
Subject: [TenTec] JUPITER FIRMWARE 1.17 TX Roll-off

> Does anyone know what the roll-off value was before
> the 1.17 upgrade?
>
> 73,
>
> Joe  K9MAN
>
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