Calibration of Heath HW-100 Tuners

Discussion in 'General Technical Questions and Answers' started by W3WCG, Nov 2, 2019.

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  1. W3WCG

    W3WCG Ham Member QRZ Page

    I am having two problems calibrating two Heathkit HW - 100 tuners. The trim capacitor at the 5500 end of the dial is at it's minimum capacitance (fully CCW) while there is plenty of inductance adjustment at the 5000 end of the dial. In addition, the scale is also non linear and can be off by as much as 10-15 khz in the center part of the dial. Is there some beginning set point at each end to start with or is it simply a back and forth tweak adjustment from both ends. The PEP output wave shape looks very good and the filament, B+ and bias voltages are OK also. I understand the tuners were built as part of the kit project but Inever saw an a calibration procedure.

    Don W3WCG
  2. K7TRF

    K7TRF Premium Subscriber QRZ Page

    The Heathkit LMO tracking adjustment is basically a back and forth affair where you try to get the dial to match known calibration frequencies at either end of the range. If you cannot achieve decent end point alignment you could have one or more fixed capacitors inside the LMO assembly that have drifted out of value or the dial mechanism may be slightly misaligned forcing you to open up the adjustment cap all the way.

    That said, it’s not unusual to have linearity and mid range tracking problems with the Heathkit LMOs especially those that were user built and not factory built by TRW.
  3. N2EY

    N2EY Premium Subscriber QRZ Page

    The HW-100 does not use an LMO. It uses a user-assembled VFO whose calibration and linearity are....what they are. Any HW-100 found today is at least 50 years old, so some of the parts may have changed value - if they were ever on-value in the first place.
    KE4OH and K7TRF like this.
  4. K9STH

    K9STH Platinum Subscriber Volunteer Moderator Platinum Subscriber QRZ Page

    The tunable oscillator in the HW-100 and HW-101 are NOT LMOs. They are just plain VFOs and Heath refers to them as a VFO.

    The calibration is no where near as good as the LMOs, especially those manufactured by TRW.

    Glen, K9STH
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  5. W7UUU

    W7UUU Super Moderator Lifetime Member 133 Administrator Volunteer Moderator Platinum Subscriber Life Member QRZ Page

    With the exception of a fair number of SB-102 LMOs from TRW that were fine on key calibration points but for the rest of the bands were pretty far off.

  6. K7TRF

    K7TRF Premium Subscriber QRZ Page

    Fair enough on the VFO vs LMO nomenclature. The points above still apply, component values may have drifted making end point calibration per the manual difficult but even if the end points can be aligned the frequency tracking across the band may or may not be very good.
  7. AI3V

    AI3V Ham Member QRZ Page

    You can try adjusting at 100 and 400 khz, but if you get within 5 khz across the dial you will be doing well.

    Rege, whose very first ham radio was a hw-101 kit.
  8. K9STH

    K9STH Platinum Subscriber Volunteer Moderator Platinum Subscriber QRZ Page


    The solid-state LMOs that were manufactured by TRW are very close in calibration across the entire 500 kHz. However, Heath used those units in the SB-303 and SB-313 receivers and often ran short where the SB-102 was involved. Some SB-102 transceivers did have TRW LMOs but the majority had LMOs made by other companies. It is those LMOs made by others that often have calibration problems.

    The non-TRW solid-state LMOs are, generally, very close at the 100 kHz points. Unfortunately, between those points, the calibration can vary all over the place.

    There was an amateur radio operator, in Florida if I remember correctly, who, for a very nominal price, would take these non-TRW LMOs and very carefully, actually very tediously, get them accurate to within 1 kHz across the 500 kHz coverage. This had to be a labor of love because what he charged would barely cover the expense of just opening the unit and definitely not doing any real work on the assembly.

    A while back, I had an SB-102 come in for service and the owner had me pull the non-TRW LMO and send it to this person for re-calibration. In a couple of weeks, the LMO came back and it was like night and day with the improvement in the calibration.

    Glen, K9STH
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  9. KX4OM

    KX4OM Ham Member QRZ Page

    The HW-101 VFO is not the same one as the HW-100, but I was able to set my HW-101 within +1 minor dial division (5 kHz) across the 500 kHz span. It took awhile to do that. I didn't have to open up the VFO to do it. I haven't checked it since the alignment in 2013, so I need to recheck it. I'll use the freq counter on the VFO output this time.

    Ted, KX4OM
    Last edited: Nov 3, 2019
  10. N2EY

    N2EY Premium Subscriber QRZ Page

    At Southgate Radio, we do things a little differently.

    The Southgate Method is simple: First, the tunable oscillator is designed, built, and adjusted to its desired frequency range. Second, the dial is fabricated, with each frequency indicated on it by checking against a BC-221 or LM frequency meter.

    Of course this won't work with a Heathkit LMO because the dial rotates five times over the course of 500 kHz. But it will work with the HW-100, HW-101 and HW-16, if you have the resources to make and calibrate a replacement plastic dial disk.


    The LM and BC-221 are wonderful pieces of test gear to have, even in this day of frequency counters, for a whole bunch of reasons - not the least of which is that they generate a signal, which is very useful for receiver testing.

    They take a bit of skill to use, because the dial isn't calibrated - you get the frequency reading the dial (including the vernier), looking in the calibration book, and interpolating. The answers are amazingly accurate.

    What I found most amazing is how they generated the calibration books for the enormous number of frequency meters made during WW2:

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