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@sbcglobal.net To: "Amsat BB" amsat-bb@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 IF unit. 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
i8CVS Domenico
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