March 2, 1973 HM-2102 Bulletin No: VHF Watt Meter HM-2102-1 Calibration Problems Reports have been received of the inability customers are having in calibrating HM-2102 on watt meter readings. This can be cured by scraping the area around the hold on the ground foil where the small spacer fits, when mounting the long bracket. See detail 3B page 7 of the manual. A good ground connection will make calibrating power readings no problem. August 10, 1973 HM-2102 Bulletin No: VHF Watt Meter HM-2102-2 Inaccurate SWR Null The shell of the input coax connector is in close proximity to the brass eyelet come in contact, the SWR cannot be accurately nulled. This is a problem area worthy of checking before any alignment is accomplished. Repositioning circuit board on angle mounting brackets will eliminate this problem. September 17, 1974 HM-2102 Bulletin No: VHF Watt Meter HM-2102-3 Calibration Circuit Correction Perform the modification as shown in the above Pictorial. (((Pictorial shows foil side of board. Instructions state to: Place C-2A close to foil side of board, solder to leads of C-2 and foil pads, then cut off excess lead length. It also lists the following values: 2 Meters 6 Meters C-2 - 15pF - PN 20-118 C-2 - 15pF - PN 20-118 C-2A - 1pF - PN 28-2 C-2A - 2.2pF - PN 28-1))) This modification will correct for the internal calibration problem and make the unit more accurate with respect to actual power input. This modification should only be done on units which have a glass epoxy board. Capacitor C2 is increased to 16 pF for 2 meters and 17 pF for 6 meters. New 16 pF and 17 pF capacitors will be in the line in the future and this modification may be used until the new capacitors are available. February 11, 1976 HM-2102 Bulletin No: VHF Wattmeter HM-2102-4 Separate High Power Calibration An article in HAM RADIO magazine [February 1976] described a modification to permit separate calibration of the high power scale. The article is reprinted below for information only; it is NOT a production change or service modification. HIGH POWER CALIBRATION FOR THE HEATH HM2102 VHF WATTMETER The great crowds of two-meter FM enthusiasts will no doubt provide the Heath Company with a continuing market for their HM2102 vhf watt meter. This dandy piece of equipment provides two switch selectable power ranges of 25 and 250 watts full scale, in the 50 to 160 MHz range, and also includes a built-in swr bridge. In checking out my wattmeter I found that everything worked fine with the exception of a noticeable discrepancy in the accuracy of the high power [250 watt] range. Checking further, I found that the problem was due to the fact that R8, a 68k resistor which is used as a meter multiplier in the 250 watt range, was out of tolerance. The problem could have been cured by replacing R8 with a new resistor, but it occurred to me that even greater accuracy could be obtained by replacing R8 with a variable 100k resistor to allow separate calibration of the high power range. This modification is easily done and works out very nicely. The small trim pot may be supported by using short pieces of solid hookup wire inserted in the PC board holes formerly occupied by R8. The adjusting slot should bace upward in the same direction as potentiometer R6. A hole in the cover plate allows access to R8 when the cover is in place. This access hole can be labeled high for high power adjust, and the hole already in the plate for R6 can be labeled “low”. The original calibration procedure calls for adjusting R6, a 50k pot, in the low power position, which also affects the high power calibration. With the addition of a 100k pot for resistor R8, the new calibration procedure is as follows: 1. Using a known power source in the 10 to 25 watt range, and/or comparing with another wattmeter of known accuracy, adjust R6 for the correct meter indication in the 25 watt range. 2. Switch to the 250 watt range, and again using a transmiter with known output, and/or a comparison wattmeter, adjust R8 for correct meter indication. Both ranges are now individually calibrated. Any further adjustment of R6 will require readjustment of R8. June 5, 1978 HM-2102 Bulletin No: VHF Wattmeter HM-2102-5 Calibration Problem If a calibration problem exists, such as power calibration and SWR null, change: C3 from 7.7 pF to 1.5 pF [PN 28-4] and R7 from 10k ohm to 5.6k ohm [PN 1-113] January 27, 1982 HM-2102 Bulletin No: VHF Wattmeter HM-2102-6 SWR Cannot Be Nulled ++++Information not available at this time++++ Thats everything I hold up to 1989 that covers the HM-2102. Enjoy!