FT-101E Intermittent Audio level/S-Meter level

Discussion in '"Boat Anchor" & Classic Equipment' started by KB3GWQ, Jun 26, 2018.

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  1. G3YRO

    G3YRO Ham Member QRZ Page

    Yes but do you get it? Maybe the high drift you noticed sometimes was due to your VFO knob moving on its own !

    Regarding the S Meter . . . if you set it using the Calibrator by the book, that should correspond to 50uV for S9 (which is the usual Amateur Radio standard) - I have checked this loads of times with an accurate Signal Generator.

    How are you basing your "S7 signal reads S9+" ? A lot of modern rigs' S Meters only read correctly when their Pre-Amp is turned on . . . otherwise it's like having an Attenuator switched in !

    Roger G3YRO
  2. KB3GWQ

    KB3GWQ Ham Member QRZ Page

    I'm more referring to how it sounds. I hear a signal that is clearly 569-579 CW (like almost perfect, but there's some noise and not super super loud) but the meter is reading 599 to 599+10db. This is on 40m, where you typically don't use a preamp. It's not a band specific problem though. I have a friend with a signal generator so maybe we can try and compare some time.
  3. G3YRO

    G3YRO Ham Member QRZ Page

    An S Meter shows how strong the signal is . . . ie how many microvolts are arriving at your antenna terminal . . . . not how strong or clear they are relative to the noise.

    If you have a zero noise level, an S3 signal can sound really loud and clear . . .

    If you have an S9 noise level, an S9 signal will probably be unreadable !
    On most rigs that enable you turn the "pre-amp" off, you need it ON if you want the S Meter to read correctly! (turning it off would be like switching in the Attenuator on the FT101).

    In fact, by-passing the first MOSFET in the FT101 would be equivalent to turning the Pre-amp off. In other words, the Pre-amp doesn't give EXTRA gain, that is the NORMAL gain . . . turning it off de-sensitizes the receiver. (and makes it less susceptible to overload or cross-mod)

    And that's what most people want to know . . . how strong you are getting their signal. (if you have a high local noise level, that's YOUR problem, not theirs!)

    Roger G3YRO
  4. N1OOQ

    N1OOQ Ham Member QRZ Page

    Wow, all this experience readily available makes me want to buy an old 101 and get it working...
  5. KB3GWQ

    KB3GWQ Ham Member QRZ Page

    OK, well I was curious about how relative it would be to my IC-746PRO or the clubs FTDX-1200 that I use from time-to-time.

  6. HS0ZED

    HS0ZED Ham Member QRZ Page

    Interesting points on the S meter and it made me go look.

    Original FT101 manual Set 14200 KHz 50 uV set Vr2 on PN1183 for S9
    FT101B manual same as original FT101
    Later FT101E, EE & EX manual. Set 14200KHz 50uV set VR2 on PB1183B for S9+25dB
    Even later FT101F manual, same as E, fairly expected.

    All on page 22 of their respective manuals

    FT101 Service manual, seems to be a collection of documents and historical data also says s9+25dB. Page 7-9

    So it looks like someone changed the books at some point. I would tend to go with the S9 at 50uV of the original, this is prety standard and even though the AGC linearity (in a log sense) is not as good as some later radios it does make the S meter read a little more realistically.

    I have a generator with a pretty good attenuator (HP), several fairly accurate step attenuators and some good measurement devices, RF milli-voltmeter, LP100, and all check out good against known references so my ability to achieve 50uV p.d. (50 ohms) is fairly okay I think.

    On my FT-101E setting VR2 for s9 with 50uV is pretty much impossible. S9+10 is pretty much end of the pots travel. I notice that R26, AGC base drive to Q4 from the AGC rectifier on the early schematic gets changed from 1M Ohm to 100K Ohm on the later radios with the seemingly higher S meter setting requirement.
  7. HS0ZED

    HS0ZED Ham Member QRZ Page

    My 2 IF boards. PB-1183C from FT-101E (S/N50345) and PB-1080A from FT-101 (S/N 24266)


  8. G3YRO

    G3YRO Ham Member QRZ Page

    If you have a calibrated Signal Generator, then obviously use that to set the the S Meter to read S9 with 50uV applied. (or did you mean that you CAN'T? Normally it's no problem to do that)

    Otherwise, using the Calibrator to set it, as per the Handbook, usually ends up pretty close. (If I remember correctly, they changed the circuitry slightly in the later rigs, hence the change in instructions)

    So what do you find if you switch between the same signal on the FT101? I think the Icom is one of the rigs that has a switch to turn off the Pre-amp . . . so you would need it ON for the S Meter to read correctly.

    Roger G3YRO
  9. HS0ZED

    HS0ZED Ham Member QRZ Page

    About the only change I can find the decrease in value of R26 from 1M to 100k, otherwise the boards of type PB-1183 look pretty much the same.

    The very early PB-1080A board has the noise blanker on it. That was off board by the time PB-1183 came along.

    Yes, with 50uV from the sig gen the LOWEST I can set the S meter with the preselector peaked is S9 + about 8-10dB. Will not go any lower. If it were meant to be set at S9 I would expect the pot range to extend below and above that.

    Calibrator signal is pretty close to 50uV on 20m so that's all good.
  10. G3YRO

    G3YRO Ham Member QRZ Page

    What you are noting is odd for 2 reasons . . .

    Firstly, if I tune in the calibrator signal, I can adjust the S Meter pot so it reads anything from 0 to full scale ! (that is what I always remember happening). Given that the pot goes directly to ground, it should obviously read zero if you turn it right down.(if you had dirty relay contacts or PCB connector, that could be why it doesn't zero, or read correctly)

    And secondly, if you set the S Meter to read S9 + 25dB on the calibrator (on 14.2), that usually corresponds to a 50uV signal reading S9 . . . or put another way, the Calibrator output is around 800uV. (in the 100kHz position . . . higher if you switch to 25kHz)

    Roger G3YRO
    Last edited: Jul 18, 2018

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