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Re: choice of IF frequencies



A 435 MHz IF would be a poor choice for a transmit converter as the third
harmonic of the IF would pass right through the printed RF bandpass filters
on the unit and cause interference to other services. 144 and 222 MHz are
the only viable choices and no one makes 222 MHz transceivers anymore. So
the existing DEM products will limit those with dual-band satellite
transceivers to mode LU (AO-13 mode L) and mode US (AO-13 mode S).

A 2400 MHz receiving converter with a 435 MHz IF would be the best way to
enable mode LS.

John
KD6OZH

----- Original Message -----
From: "Estes Wayne-W10191" <Wayne_Estes-W10191@email.mot.com>
To: <amsat-bb@AMSAT.Org>
Sent: Thursday, 07 December 2000 20:23 UTC
Subject: [amsat-bb] choice of IF frequencies


> Ed Cole wrote:
>
> I just pre-ordered* my 1269 Tx conv. & 10451 Rx conv. from Steve [DEM]
this morning and the schedule sounds about right.  They are holding on
production to be sure of which AO-40 modes checkout good, and for some
verification of link requirements by actual observation {i.e. if they make a
bunch of 10w convertors and you need 20w...they are stuck with unwanted
inventory}.
>
> Wayne Estes replies:
>
> I notice that DEM's 1269 transmit converter and the 2400 MHz MHz RX
converter both have 144 MHz IF's.  Why?
>
> It seems obvious to me that AO40 transmit and receive converters should
use DIFFERENT IF's.  The logical choice for the transmit IF is 435 MHz.
Then the 2400 MHz and 1269 MHz converters would be "plug and play" with
EVERY commercially made satellite transceiver, including models that don't
have HF capability.
>
> This seems even more compelling if AO-40's 435 MHz transmitter really
turns out to be dead.  435 MHz would be an "uplink only" band, perfect as
the IF for ALL AO-40 transmit converters.
>
> Has anybody asked DEM why they don't plan to offer the 1269 MHz transmit
converter with a 430 MHz IF?  Is something wrong with my logic?
>
> Wayne Estes W9AE
> Mundelein, IL, USA
>
> p.s. I just re-subscribed to AMSAT-BB.  I used to be active on AMSAT-BB in
the AO13 days with callsign WD5FFH.
>
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