IC7100 FM TX issues on all bands: power varies with modulation.

Discussion in 'Radio Circuits, Repair & Performance' started by IZ4UFQ, Feb 10, 2019.

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  1. IZ4UFQ

    IZ4UFQ Ham Member QRZ Page

    I have bought an used IC7100, not modified (no SSB power mod), latest firmware installed (Release E5 from 2016).

    I was testing the radio for the notorious SSB TX power issue, which is in fact non-existent, my Bird 4391 wattmeter shows a proper 100W PEP in HF by using the PEP power measurement function.

    While I was at it, I tested the power in all bands and all modes, and noticed an anomaly: power goes up with modulation even when it should not (that is, in FM mode).

    For example, in UHF FM at full power (30W nominal) I get 30 W if I stay silent, but I get 35W if I whistle in the mike.

    This happens also in VHF FM, power goes from 47 to 57 W when modulating, and it happens in HF too (10 meters FM).

    If I set RF power to a lower value (20% for example) the effect is even more evident: in HF (10 meters FM) I get 25W if I do not speak in the mike, and more than 60 (my Bird shows overflow with a 50W slug) if I whistle in the mike.

    What's happening? Is my IC7100 modulating in FM with some spurious AM modulation?

    I have tried resetting the radio (from the menu) but the issue remains.
     
  2. KA5IPF

    KA5IPF Ham Member QRZ Page

    You need to look at it on a 'scope. It will show if the power out is not stable in FM mode.
     
  3. IZ4UFQ

    IZ4UFQ Ham Member QRZ Page

    Since I also see the supply current increase in a significant way when the ouput power seems to increase I presume that the ouput power is really increasing.

    It should be interesting to check if another 7100 behaves in the same way, but I don't have another one available.
     
  4. IZ4UFQ

    IZ4UFQ Ham Member QRZ Page

    Just for info, I have discussed the issue in an italian language forum, too.

    To sum it up, it seems that other Icom radio with DSP modulator show a similar behaviour.

    Icom ic 821H - analog FM modulator
    Icom ic 756 pro3 DSP modulator
    Icom ic 7600 DSP modulator

    821H (144.5 MHz) unmodulated carrier 40W, modulated (1KHz - dev. 5KHz) 40,3w
    PRO3 (50 MHZ) unmodulated carrier 50W, modulated (1KHz - dev. 5KHz) 63W
    7600 (50 MHZ) unmodulated carrier 50W, modulated (1KHz - dev. 5KHz) 58W

    I still have not found another IC7100 for comparison.

    Here is the link to the italian forum discussion:

    http://www.arifidenza.it/Forum/topic.asp?rand=7055475&whichpage=1&TOPIC_ID=344538&#686226
     

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