Kenwood TH78A Instructions page 4

NOTE: One version of the mods I collected stated that removing "diode D8" would open up the 300
MHz band for listening to the aircraft band. I'm relating it because the information is out there being
circulated. If you look at the schematic, D8 appears to be reverse polarity protection for the lithium
backup battery. I advise against removing it since the D5 removal gives access to same bands. Also this
mods says to hold the "F" key for 1 second then press "TONE (low)" to get into the band (after the mod
is done). This is how you change your TX power level, how are you supposed to do it after the mod?
I've made these mods (except for the above note) on my radio and they DO work. As for increased
intermod problems, I haven't noticed any yet. Best as I can tell the full range of tuning is 50 MHz to
999.999 MHz. There are gaps in the coverage, for example 180 MHz to 300.000 MHz. I used some test
equipment at work, specifically an HP 8656B industrial signal standard with the ultra-high stability
oscillator ($20,000 total cost for that baby). The following is a list of receiver sensitivities at various
frequencies. I used 12 dB SINAD with +/- 3 KHz deviation, and the volume set to 13 on the radio.
End of part 6
Frequency (MHz)
============================================
50.000 251 millivolts at 100% modulation AM
100.000 .55 microvolts at 100% modulation AM
125.000 .120 microvolts at 100% modulation AM
150.000 .127 microvolts
179.995 .55 microvolts
300.000 1.15 microvolts
350.000 2.95 microvolts
390.000 1.25 microvolts
400.000 5.95 microvolts (odd I know, but that's what it did)
450.000 .14 microvolts
500.000 115 microvolts
511.9875 385 microvolts
800.000 1.2 microvolts
850.000 .499 microvolts
900.000 1.55 microvolts
950.000 1.90 microvolts
Anyone with more info on the TH78a, please send it my way and I'll add it to this file. I can be reached
at the following locations:
Ken Mazie - Sysop, Quasatron Systems BBS (landline) at 510-846-6085.
or - KD6IZY @ WA6YHJ.#nocal.ca.usa.na for AX.25 packet
or - KD6IZY.ampr.org [44.4.30.134] for TCP/IP
That completes the mod file.
73, Chuck (kd6izy)
NOTE... The above contact info is no longer valid. I can however be reached via Quasatron.com.
Sensitivity