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Thread: XTL1500 Preselector alignment for out of band ham use?

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    Default XTL1500 Preselector alignment for out of band ham use?

    Hello to the group, really enjoying the site and my new 450-512 XTL1500 that I picked up from that PG county auction. I have it working just fine in the 440 ham band, and it makes spec at 0.25uV. I'm just wondering if anyone has bothered to re-align the preselector using the Tuner software to make it better out of band (PG was on 495).

    I have the detailed service manual and don't really think I need to, but just curious since it's installed already in the car.

    Thanks!


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    Actually I think I found the answer in the Astro25 tuner help files for the Receiver Alignment Menu:

    Procedure for VHF band

    All VHF radios operate to specification using the same set of default Front End filter values and so no tuning is required. Do not adjust the values that have been pre-programmed into the radio. For some VHF radios, this screen might not be available.

    Procedure for UHF band

    All UHF radios operate to specification using the same set of default Front End filter values and so no tuning is required. Do not adjust the values that have been pre-programmed into the radio. For some UHF radios, this screen might not be available.

    700 and 800 Mhz radios do have a procedure that uses a -90dbm signal and adjusting the RSSI sliders across those bands.



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    Mine works just fine as tuned, I've never had to re-tune any of the S split XTLs that I have used on the Ham bands.

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    Actually what I found out was a setting called "RF AGC" was turned on, which was making me think the receiver was less sensitive than the MCS2K that it replaced. That's what happens when you get a "new to you" box without default settings. The RF AGC switches in and out an attenuator to fight intermod, and this setting determines the aggressiveness.

    Once I changed this setting back to "Disabled" the fluttery signals stopped. They were happening across the whole range so it was not just out of band 440 stuff.

    Here is the screen shot and help text description. Probably most XTL's don't have this set, but it might help someone else that questions their new toy.

    RF-AGC.JPG

    Advanced RF AGC
    (Conventional Personality, Advanced)

    Selects the type of Radio Frequency (RF) Automatic Gain Control (AGC) that applies for the current Conventional Personality.

    Disabled: Note: Even when "Disabled" the radio employs a basic form of AGC which helps to avoid signal clipping and receiver overload that may damage radio components under extremely high signal strength conditions.

    Standard: Enables a form of RF AGC which attempts to protect against IM (Inter-Modulation) interference by continuously adjusting received signal attenuation such that the receiver is operated in a range of signal strength where its IM rejection is optimal.

    Enhanced: Enables the same basic operation as the "Standard" setting, except that the number of changes in signal attenuation is minimized when the received signal strength is near the switching threshold; thus avoiding attenuator "chatter".

    "Standard" and "Enhanced" Advanced RF AGC may degrade performance on channels that do not experience any IM (intermodulation) interference. Therefore, only enable these selections on channels known to experience IM interference.
    Last edited by motoham88; Dec 25, 2012 at 11:43 AM.

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    That's a good bit of information; I was wondering what that setting did, and hadn't explored it yet. There's probably very few cases where you'd ever want that on, it sounds like it's good for heavy metro interference only.

    FYI, the reason they don't want you messing with the front ends is they are probably doing something called "stagger tuning" which is to NOT set the peaks all at the center of the band, but to alternate stages at a high and low frequency to make a wide-band filter with less overall gain than if it was center-tuned, which would make it narrower but pass more signal. This goes back to the old Syntor X/X9000 days where you had do do something like this to get good sensitivity over the entire band range the radio covered. I suspect they are doing this at the factory to get better wide band performance out of the front ends.