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!
