[amsat-bb] Re: 145 MHz IF on V/s?
kl7uw at acsalaska.net
Mon May 19 07:29:07 PDT 2008
I agree with Dom's analysis. What you are facing is almost the
classic problem of running in-band duplex (that is the problem every
repeater faces). One solution would be to use a repeater duplexer
tuned for your 720-KHz split. However there is a catch: duplexers
normally operate at a single channel frequency and do not allow
tuning a subband. If you are running low power you might be OK with
bandpass filters tuned for a wider band acceptance on the receive frequency.
So if you can receive on 123-MHz this is infinitely
easier/cheaper. I run 123-MHz on one of my Drake converters with no
problems from 145 MHz transmissions. MY other Drake is modified for
IF of 435 MHz which makes mode-LS simple as I nver have to face your dilemma.
73 Ed - KL7UW
At 03:37 AM 5/19/2008, i8cvs wrote:
>----- Original Message -----
>From: "K & R Yoksh" <yokshs at sbcglobal.net>
>To: "Amsat BB" <amsat-bb at amsat.org>
>Sent: Monday, May 19, 2008 12:56 AM
>Subject: [amsat-bb] 145 MHz IF on V/s?
> > Hi all,
> > Thanks for the replies, however, I've still not had my question answered,
> > so I'll ask again.
> > I'd like to hear from anyone using a 145 MHz IF when working mode V/s. Do
> > you experience desense when operating V/s, but not other uplink modes?
> > I'm planning to use my AIDC 3731 with 145 MHz IF when I install my dish
> > this summer. I really want to use it for HEO operation, but it'd be a
> > bonus if I could also work the LEOs.
> > I could go with a 123 MHz IF unit if that'd work better.
> > Thanks and 73,
> > Kyle Yoksh
> > K0KN
> > Olathe, Kansas
>Hi Kyle, K0KN
>Don't warry about to use 145 MHz IF for HEO operation because P3-E
>will use the V band only for downlink.
>The builders of P3-E are aware of the problem and they don't want to
>complicate the life to the users.
>For the LEOs S band using downconverters 2400-2402 MHz with an IF
>144-146 MHz :
>Receiving AO-51 at 2401.200 MHz the IF fall into 145.200 MHz and
>transmitting at 145.920 MHz FM the difference between the IF and TX
>frequency is 720 kHz
>In this condition there are three possible outcomes:
>The 145.200 MHz uplink signal is picked up directly by the cable after
>the mixer of the S band converter and sent down to the shak into your IF
>receiver flowing in general through the outside surface of the braid of
>the coax cable. (common currents)
>The 145.200 MHz uplink signal can pass directly through the converter
>first stage up to the IF receiver in the shak.
>The 145.200 MHz uplink signal is picked up directly by your IF receiver
>because your power is very high and TX/RX are very close.
>Since there are many variables involved mostly depending on your TX power
>it is very difficult to say yes or not and so a test to see if you will
>suffer or not a desensing is mandatory.
>If you have a desensing there are many possible cures for it but if you
>don't have the time to work on this problem it is best to use your 123 MHz
>I remember that receiving AO40 I got interference over the 2401.323 MHz
>bpsk beacon when an amateur friend living few miles away of me was locally
>transmitting FM using high power at 145.325 MHz
>145.325 MHz was at the same time his own frequency and my IF frequency.
>My investigation demonstrated that the interfering signal was piched up
>directly by the coax cable running from the S band downconverter to the
>IF receiver in the shak.
>Unfortunately i don't had on hand a S band downconverter with a 123 MHz IF
>Best 73" de
>Sent via AMSAT-BB at amsat.org. Opinions expressed are those of the author.
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