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Those of you who have an Omni Six/Six Plus that exhibit a slight =
transmitted CW chirp may be in for some good news. George, W2VJN at =
INRAD has agreed to manufacture a 2.8 kHz BW 9 MHz I.F. filter if we can =
demonstrate enough of a demand for it. This is a replacement filter for =
the stock 2.4 kHz BW 9 MHz filter. This is the only filter in the Omni =
that shares the receive and transmit function. This same filter also =
exacerbates the slight chirp caused by frequency-shift-keying the Omni's =
9 MHz BFO circuit board on some Omnis. =20
How can you tell if your Omni is transmitting with chirp? Yes, of =
course you listen for it. But in many cases is can be subtle. It's =
when you compare the CW note against another Ten-Tec when you notice the =
difference the most. Here's a test you can use: key your transmitter in =
the CW mode, sending a string of characters, listening carefully to the =
CW note on another receiver. It's best to use a wide SSB bandwidth for =
monitoring. Next, depress the Omni's FSK mode button. Again. key the =
transmitter by sending a string of characters, listening for any change. =
In FSK, the CW transmit circuit is identical, with the only exception =
being that the sidetone monitor is disabled, but more importantly....the =
transmit BFO frequency is HIGHER than it is in CW, placing the CW well =
above the lower skirt of the 2.4 kHz filter. If CW sounds cleaner to =
you in FSK than it does in CW, you've got the problem I'm discussing =
here. =20
I want to make this point clear: the problem does NOT manifest on all =
Omnis. Nevertheless, on those that are not problematic of a chirp, the =
CW BFO transmit offset frequency of 9,000.400 is running dangerously =
close to the 2.4 kHz filter's lower passband skirt. When the CW =
transmit BFO frequency reaches the filter skirt, chirp results and the =
transmitted CW waveform can become truncated on the trailing edge.=20
Recall that the Omni's CW transmitted BFO frequency is 9,000.400 kHz. =
The center frequency for this filter is mid-way between the LSB and USB =
transmitted BFO frequencies at 9,001.500 kHz. Therefore, the margin of =
lower skirt freedom in the designed Omni Six/Six Plus is only 100 Hz; =
the filter cuts off at 9,000.300 kHz. If the filter is not near =
perfection in manufacturing, the CW BFO frequency can indeed fall square =
on the filter's edge as it does in two of my Omni Sixes. =20
Other's have repeatedly asked me why the Omni V sounds so consistently =
good on CW transmit in comparison with some Omni Sixes. With the Omni =
V's CW circuitry being a close 99% match to that of the Omni Six, the =
answer again lies with this filter. Only in the Omni V, the fixed CW =
offset is 9,000.600 kHz, well out of harms way of the lower filter =
skirt. Here, the Omni V has a margin of freedom of 300 Hz, not 100 Hz =
as in the Omni Six series.
A 2.8 kHz BW, 9 MHz I.F. filter will provide for the same 300 Hz of =
safety to the lower filter skirt. While this corrects the problem on =
CW, how will it affect SSB operation? If the USB and LSB BFO =
frequencies remain the same, the audio response goes from 300Hz - 2.7 =
kHz to 100 Hz- 2.9 kHz. As a practical matter, this should not present =
a problem. Yes, the occupied bandwidth is slightly greater, but not so =
much as to cause QRM to QSOs near your operating frequency. As a side =
note, Kenwood once sold a filter with this bandwidth and the Yaesu =
FT-1000MP has a menu choice for expanded transit SSB audio response. =
Also, since the USB and LSB frequencies are adjustable, the audio =
passband characteristics could be shifted slightly if desired.
A minimum of five brave souls are needed for George to make this filter. =
Cost of the filter to us is $110. Shipping is 2 months ARO.
If you have an interest in this, please e-mail me directly and I will =
forward your commitment to George. Thanks.
-Paul, W9AC
Jacksonville, Florida=20
-----Original Message-----
From: George Cutsogeorge <w2vjn@rosenet.net>
To: Paul Christensen <paulc@mediaone.net>
To: <tentec@contesting.com>
Date: Tuesday, October 06, 1998 5:01 PM
Subject: Re: Omni Six Filter
Hi Paul,
=20
Glad you were able to isolate the problem. We can have a 2.8 centered =
on 9001.5 made with similar specs to our 2.1. If you can get 4 or 5 =
orders together, we will order 10 pcs. Our minimum order is 10, so we =
like to know some of them will sell. Delivery is about 2 months ARO.
=20
George
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<BODY bgColor=3D#ffffff>
<DIV><FONT color=3D#000000 size=3D2>Those of you who have an Omni =
Six/Six Plus that=20
exhibit a slight transmitted CW chirp may be in for some good =
news. =20
George, W2VJN at INRAD has agreed to manufacture a 2.8 kHz BW 9 MHz I.F. =
filter=20
if we can demonstrate enough of a demand for it. This is a =
replacement=20
filter for the stock 2.4 kHz BW 9 MHz filter. This is the only =
filter in=20
the Omni that shares the receive and transmit function. This same =
filter=20
also exacerbates the slight chirp caused by frequency-shift-keying the =
Omni's 9=20
MHz BFO circuit board on some Omnis. </FONT></DIV>
<DIV><FONT color=3D#000000 size=3D2></FONT> </DIV>
<DIV><FONT size=3D2>How can you tell if your Omni is transmitting with=20
chirp? Yes, of course you listen for it. But in many cases =
is can be=20
subtle. It's when you compare the CW note against another Ten-Tec =
when you=20
notice the difference the most. Here's a test you can use: key =
your=20
transmitter in the CW mode, sending a string of characters, listening =
carefully=20
to the CW note on another receiver. It's best to use a wide SSB =
bandwidth=20
for monitoring. Next, depress the Omni's FSK mode button. Again. =
key the=20
transmitter by sending a string of characters, listening for any =
change. =20
In FSK, the CW transmit circuit is identical, with the only exception =
being that=20
the sidetone monitor is disabled, but more importantly....the transmit =
BFO=20
frequency is HIGHER than it is in CW, placing the CW well above the =
lower skirt=20
of the 2.4 kHz filter. If CW sounds cleaner to you in FSK than it =
does in=20
CW, you've got the problem I'm discussing here. </FONT></DIV>
<DIV><FONT color=3D#000000 size=3D2></FONT> </DIV>
<DIV><FONT color=3D#000000 size=3D2>I want to make this point clear: the =
problem=20
does NOT manifest on all Omnis. Nevertheless, on those that are =
not=20
problematic of a chirp, the CW BFO transmit offset frequency of =
9,000.400 is=20
running dangerously close to the 2.4 kHz filter's lower passband =
skirt. =20
When the CW transmit BFO frequency reaches the filter skirt, chirp =
results and=20
the transmitted CW waveform can become truncated on the trailing edge.=20
</FONT></DIV>
<DIV><FONT color=3D#000000 size=3D2></FONT> </DIV>
<DIV><FONT size=3D2>Recall that the Omni's CW transmitted BFO frequency =
is=20
9,000.400 kHz. The center frequency for this filter is mid-way =
between the=20
LSB and USB transmitted BFO frequencies at 9,001.500 kHz. =
Therefore, the=20
margin of lower skirt freedom in the designed Omni Six/Six Plus is only =
100 Hz;=20
the filter cuts off at 9,000.300 kHz. If the filter is not near =
perfection=20
in manufacturing, the CW BFO frequency can indeed fall square on the =
filter's=20
edge as it does in two of my Omni Sixes. </FONT></DIV>
<DIV><FONT size=3D2></FONT> </DIV>
<DIV><FONT size=3D2>Other's have repeatedly asked me why the Omni V =
sounds so=20
consistently good on CW transmit in comparison with some Omni =
Sixes. With=20
the Omni V's CW circuitry being a close 99% match to that of the Omni =
Six, the=20
answer again lies with this filter. Only in the Omni V, the fixed =
CW=20
offset is 9,000.600 kHz, well out of harms way of the lower filter =
skirt. =20
Here, the Omni V has a margin of freedom of 300 Hz, not 100 Hz as in the =
Omni=20
Six series.</FONT></DIV>
<DIV><FONT size=3D2></FONT> </DIV>
<DIV><FONT size=3D2>A 2.8 kHz BW, 9 MHz I.F. filter will provide for the =
same 300=20
Hz of safety to the lower filter skirt. While this corrects the =
problem on=20
CW, how will it affect SSB operation? If the USB and LSB BFO =
frequencies=20
remain the same, the audio response goes from 300Hz - 2.7 kHz to 100 Hz- =
2.9=20
kHz. As a practical matter, this should not present a =
problem. Yes,=20
the occupied bandwidth is slightly greater, but not so much as to cause =
QRM to=20
QSOs near your operating frequency. As a side note, Kenwood once =
sold a=20
filter with this bandwidth and the Yaesu FT-1000MP has a menu choice for =
expanded transit SSB audio response. Also, since the USB and LSB=20
frequencies are adjustable, the audio passband characteristics could be =
shifted=20
slightly if desired.</FONT></DIV>
<DIV><FONT size=3D2></FONT> </DIV>
<DIV><FONT size=3D2>A minimum of five brave souls are needed for George =
to make=20
this filter. Cost of the filter to us is $110. Shipping is 2 =
months=20
ARO.</FONT></DIV>
<DIV> </DIV>
<DIV><FONT color=3D#000000 size=3D2>If you have an interest in this, =
please e-mail=20
me directly and I will forward your commitment to George. =20
Thanks.</FONT></DIV>
<DIV><FONT color=3D#000000 size=3D2></FONT> </DIV>
<DIV><FONT color=3D#000000 size=3D2>-Paul, W9AC</FONT></DIV>
<DIV><FONT color=3D#000000 size=3D2>Jacksonville, =
Florida </FONT></DIV>
<DIV> </DIV>
<DIV><FONT face=3DArial size=3D2><B>-----Original =
Message-----</B><BR><B>From:=20
</B>George Cutsogeorge <<A=20
href=3D"mailto:w2vjn@rosenet.net";>w2vjn@rosenet.net</A>><BR><B>To: =
</B>Paul=20
Christensen <<A=20
To: <tentec@contesting.com>
href=3D"mailto:paulc@mediaone.net";>paulc@mediaone.net</A>><BR><B>Date:=
=20
</B>Tuesday, October 06, 1998 5:01 PM<BR><B>Subject: </B>Re: Omni Six=20
Filter<BR><BR></DIV></FONT>
<DIV><FONT size=3D3>Hi Paul,</FONT></DIV>
<DIV><FONT size=3D3></FONT> </DIV>
<DIV><FONT face=3D"" size=3D3>Glad you were able to isolate the =
problem. We=20
can have a 2.8 centered on 9001.5 made with similar specs to our =
2.1. If=20
you can get 4 or 5 orders together, we will order 10 pcs. Our =
minimum=20
order is 10, so we like to know some of them will sell. Delivery =
is about=20
2 months ARO.</FONT></DIV>
<DIV><FONT face=3D"" size=3D3></FONT> </DIV>
<DIV><FONT face=3D"" size=3D3>George</FONT></DIV></BODY></HTML>
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