不懂外文！请翻译一下！the differences between icom ic-781 and ic-780 (japanese version of ic781)
in my product review of ic7800 and ic781 written in april 2007
http://www.ab4oj.com/icom/ic7800/7800v781a.pdf (mirror), i mentioned that i used the ic780 (japanese version of ic781) as the test transceiver. after that, i have been receiving enquiries about the differences between ic781 and ic780. i have done some research and would like to summarize my findings in the following paragraphs.
1. circuitry and structure
the header of the schematic diagrams supplied with the ic780 is ??????ic-780 ic-781 schematic diagrams??????. with close examination and comparison with the schematic diagrams downloaded from internet, i did not notice any difference.
i also had a copy of the service manual of ic780 in japanese. after comparing with the ic781 service manual downloaded from the internet, i could not find any difference except for the adjustment of output power (discussed in paragraph 3 below). although my japanese is nothing brilliant, i would comfortably conclude that both ic781 and ic780 are electrically the same.
2. frequency allocation
as some of you may be aware the frequency allocation of ham bands (hence tx frequencies) in japan is more restrictive especially in the 160m, 80m and 40m bands.
however, the modification of general tx coverage for ic780 is easy. simply cut r80 in the logic ??????b?????? unit then you will have continuous tx coverage from 1.8 ?????? 29.9mhz. the logic ??????b?????? unit is easily accessible by opening up the top cover.
3. output power
the output power of ic781 and ic780 are 150 watts and 100 watts respectively. the japanese ham license legislation in the old days restricted the maximum power of hf transceivers to 100 watt. perhaps, this explains why the output power of ic780 was 100 watts.
as mentioned in paragraph 1 above, both ic781 and ic780 are electrically identical. the final pa transistors are the same ?????? mrf422. ic780 can be retuned to deliver 150 watts by simply adjusting r49 in the if unit ?????? see page 6-22 of the ic781 service manual. no other adjustment is required. the if unit can be easily accessed by opening up the bottom cover.
4. ac main voltage in japan
the ac main voltage in japan is 100v as against the 120v in us. since the designed operation voltage of ic781 / ic780 is 100v, the famous heating problems in the reg unit of ic781 are less serious in the case of ic780.
the switching of operation voltage from 100v to 200v is not difficult for ic780. it can be done by swapping p2 from j1 to j2 of the pi unit. the pi unit is situated under the scope unit.
upon arrival of hong kong, i switched the operation voltage of my ic780 to 200v. since the ac main voltage in hong kong is 220v, i installed a computer fan to cool down the reg unit at the rear.
5. product life of ic780
most ic781s were actually manufactured 1989-1993. the ic780 continued in ??????production?????? later and was being sold by icom japan until the very early 2000s. in other words, the chance of getting a ??????younger?????? ic780 is higher.
6. serial number
in case of ic781, serial numbers after 2xxx have been considered as late productions. ic780s are solely for japanese domestic market and have their own serial numbers. therefore, serial numbers after 17xx will be considered as late productions.
7. sourcing ic780 in japan
local japanese second hand radio dealers are reluctant to entertain any overseas purchase. perhaps, the local market has already been big enough for them and communication in english with foreigners for overseas sales is not common. all my communication with the radio dealers in japan is in japanese.
therefore, the most straight forward way to get a second hand ic780 would be to buy it while you have a trip in japan.
disclaimer
no responsibility is assumed for the accuracy of any material presented above, or for the consequences of its use.
73 johnny siu vr2xmc
may 2007
copyright @ johnny siu vr2xmc. all rights reserved.
