Well the 9 MHz boards on the Omni V and Omni VI from the RX input to the 2.4
kHz filters are virtually the same. Many of the connectors and parts have
the same numbers. There are some slight differences (in/out refers to the
roofing filter):
Omni V Omni VI
Filter bandwidth 12 kHz 15 kHz
Fixed in/out caps on filter 33 pF 18 pF
Variable in/out caps 4-20 pF 4-20 pF
Chokes in/out 8.2 uH 10 uH
Bypass caps in/out to GND 120 pF N/A
Note: The bypass caps are on the RX input prior to the filter chokes
and padding caps AND on the output side after the padding caps and choke.
It's interesting that these caps are C1 and C6 respectively on the Omni V.
A quick examination of the Omni VI schematic shows that part numbers C1 and
C6 don't exist! On the Omni VI the 3 transistors in this stage have all
been changed to generic 2N3904s but biasing remains unchanged from the Omni
V.
In summary, with the possible exception of the padding caps on the filter,
it looks, in my opinion, like the filter mod might also be applicable to the
Omni V!
Thanks to Greg (K7KJ) for the Omni VI schematic info.
Anxiously awaiting more info from InRad!
73,
Rick
VE7TK / VE7ASR
Website: http://www3.telus.net/ve7tk
-----Original Message-----
> From: Rick Williams [mailto:rick.williams@telus.net]
> Sent: May 21, 2004 15:08
> To: TenTec (E-mail)
> Subject: Re: [TenTec] INRAD filter for OMNI VI/Plus series ... maybe
> Omni V?
>
>
> On the Omni V schematic the 2-pole roofing filter "restricts
> the receive bandwidth to about 12 kHz for FM reception and also
> prevents strong out of band signals from reaching the noise
> blanker circuits." That is the NB is downstream of the 2-pole filter.
>
> Now for me the question is "How similar are the 9 MHz board on
> the Omni V and Omni VI?" If the same roofing filter is used in
> both then perhaps the Omni V could be improved as well by a
> better roofing filter.
>
> In the next couple of days I hope to get a copy of the Omni VI
> schematic and compare!
_______________________________________________
TenTec mailing list
TenTec@contesting.com
http://lists.contesting.com/mailman/listinfo/tentec
|