QRZ! Ham Radio 20/QRZ Ham Radio Callsign Database - Volume 20.iso/modfiles/th79a.txt

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Kenwood TH79 Dual Bander Modification and Feature Guide  r1.5  9/13/94
=======================================================================
Clayton Wagar, KD4IDN
920 West Crawford Street #7
Dalton, GA 30720

Here is a compiled list of modifications and features I've found for the
Kenwood TH79 Dual Band HT.

Thanks to the following for their contributions to this document:
    Mike Musick, N0QBF
    Cole Cunningham, AA7RD
    Duane Voth, KC5BGV
    Chuck Scott, N8DNX

Having had many other radios in the past, and certain to have many in
the future, I understand the anticipation of Amateur Radio operators to
find modifications to their equipment. I started this document because I
want to see _quality_ information circulated as quickly as possible, in
order to save a lot of time and effort for others.

If you have any other comments, mods, or information you would like to see
included in this document in the future, please send them to:
        Clayton Wagar KD4IDN
        [e-mail]

Outstanding questions at the time this document was released:

* Rumor of a keypad modification to the radio for "Wide band" TX, RX. If you
  know of this mod, please write to me, even if you wish it not to be
  published. This would save a number of poor radios from useless torture!

Hope you find all of this information useful. Again, please send corrections
or additions to [e-mail]

73 de Clayton
KD4IDN

+++++++++++++++++++++++++++++++++++++++++++++++++++++++++++++++++++++++
Contents of This Document
+++++++++++++++++++++++++++++++++++++++++++++++++++++++++++++++++++++++

I.    Disclaimer and other foolery
II.   Brief Description of the Kenwood TH79A Dual Band Handheld Radio
III.  MARS/CAP Modification
IV.   Extended TX/RX Modification ('Beyond MARS')
V.    Remote Base Operation
VI.   Post Modification Specification Chart
VII.  Cross Band Repeat
VIII. Other Stuff

+++++++++++++++++++++++++++++++++++++++++++++++++++++++++++++++++++++++
I. Disclaimer
+++++++++++++++++++++++++++++++++++++++++++++++++++++++++++++++++++++++

Well, don't you get sick of this stuff? I know, I know. However, I must
say that I cannot and will not be responsible for anything that might
happen to your radio, your person, your dog, or other operators you
might talk to with your th79. In addition, if you decide that, with
your newly modified HT, you just absolutely must cause unlawful
interference with another ham or another radio service, I won't pay your
NAL. Really.

Oh, and while we're at it... The extended RX/TX modifications may
require you to solder or desolder really, really small components. If
you want to know how small, look at the tip of an average ball point pen.
Smaller than that. It takes about 1/2 of a second to wipe out several
components as well as fry the board inside the 79. Please be careful.

+++++++++++++++++++++++++++++++++++++++++++++++++++++++++++++++++++++++
II. TH79 Description and Impressions, by Mike Musick, N0QBF
+++++++++++++++++++++++++++++++++++++++++++++++++++++++++++++++++++++++

Lulled by the sexy small size, I succumbed (or, rather, the
credit card succumbed) and bought a Kenwood TH-79 dual-band H-T
recently. Already owning a TH-78, the comparison comes easy.

SPECS. The TH-79A is a U.S.-spec dual-band transceiver, featuring
coverage from 144-148 and 438-450 MHz. Receive coverage is
extended on the 2M side from 118 to 174 MHz with AM in the
aircraft band; there is no extended UHF coverage without
modification. Max power is rated 5W on VHF and 3.5W on UHF with a
12V source; max power with stock 600 mAH nicad pack is 2.5/2.0.
There are three power levels for each band - high, low, and
extra-low (30mW). There are 80 memory channels, with no evident
expansion capability. U.S./Canada version comes with the CTCSS
encode/decode option. Going price at a 7/17/94 hamfest was $480.

GENERAL IMPRESSIONS. Tiny, tiny, tiny. Imagine putting a small
duckie on the ARRL Repeater Directory - except that the 79 is
narrower by about an inch. With the standard battery and not
counting the belt clip, the dimensions are roughly 2" wide, 5"
tall, and 1" thick. The belt clip adds 3/8" to the thickness; I
left it off so it would be pocketable, and, frankly, it fits
moderately comfortably in my work slacks' front pockets, which
was surprising. It's tiny! (Oh, I said that already.)

The 79's keyboard has larger buttons than it's predecessor (lacks
the cover, too) which are much easier to use. Control layout in
general is better and even in just a couple of days I appreciated
the change. No more ambiguous power switch - it's in the primary
band volume knob in a normal OFF/ON/VOL setup. Secondary band
volume control is on the "ring" of the freq/channel encoder knob
in a coaxial arrangement.

There are no squelch knobs; it a key+knob function for both
bands. Squelch control was, well, interesting. There are only six
"settings", with usually only the lowest setting opening the
squelch under no signal. Reading between the lines in the manual,
apparently the squelch circuit is semi-automatic. I expected some
limitations, but had no complaints under actual use - it worked
well.

With my expected habit of putting it in my pocket, I like the
control lock switch - it's *not* an F-key function, but, rather
is a slide switch next to the PTT. No more fumbling around to
unlock it. Unfortunately, the lock function does not lock PTT -
that has to be disabled with the "Tx Stop" menu setting. I found
this out the hard way by putting it in my pocket and
inadvertently keying-up a repeater.

The 79 has an alphanumeric display capability of two lines of 10
characters, which is used in several ways. First, there is a
"guide" facility, which provides online instruction for most
operation features with a scrolling display. Then there is a
"menu" function, which provides access to the settings which were
normally done with obscure F-key commands in the 78. Setting the
various functions is very clear this way. There is also a status
review mode, where the more important settings are displayed.

Finally, the alphanumeric display can be set for each programmed
channel. Seven characters positions are available, and almost the
entire extended ANSI character set - that's right: lower case,
symbols, and accented characters - can be used. However, alpha
display is mutually exclusive with frequency display. Frequency
display mode can be selected in case you forgot what was
"underneath" your programmed channel ID.

+++++++++++++++++++++++++++++++++++++++++++++++++++++++++++++++++++++++
III. MARS/CAP Modification provided by Mike Musick, N0QBF
+++++++++++++++++++++++++++++++++++++++++++++++++++++++++++++++++++++++

Here is the MARS/CAP modification for the new Kenwood TH-79A
dual-band HT. Usual disclaimers about doing mods apply.

1. Remove battery.

2. Open case by first removing 3 screws (#00 Phillips) on back
and 1 screw on side hidden underneath the rubber flap covering
the DC power jack. Gently pry apart starting at top; BNC
connector will move with back, knobs with front.

3. Spread unit out. Wires will "hinge" on the side with the PTT
button.

4. Looking on the back of the keypad (front) half, locate green
wire on upper left, just below the CTCSS decoder module.

5. Neatly cut this green wire, and tuck back in so ends won't
touch each other or other components.

6. Reassemble.

Programmed memory will be lost since the CPU will notice the
strap change and reset itself.

End result -

   Before: VHF RX - 118.000-173.995  TX - 144.000-147.995
           UHF RX - 438.000-449.995  TX - 438.000-449.995

   After:  VHF RX - 118.000-173.995  TX - 142.000-151.995
           UHF RX - 420.000-449.995  TX - 420.000-449.995

Automatic repeater offset and shift selections remain normal.

And this tip comes from Duane Voth, KC5BGV...

"The MARS/CAP mod can be made without opening the entire case up.  You
can fairly easily cut the green wire by simply (and carefully) removing
the CTCSS decoder cover and using a small pair of diagonal wire cutters."

+++++++++++++++++++++++++++++++++++++++++++++++++++++++++++++++++++++++
IV. "Wide Band" Modification, provided by Cole Cunningham, AA7RD
+++++++++++++++++++++++++++++++++++++++++++++++++++++++++++++++++++++++

Following is a modification for the Kenwood TH-79A Dual Band HT which
opens it up to tuning from 67-174 MHz and 400-511 MHz.  Actual receive was
85-135.995 AM and 136-179.995 FM with reasonable (0.5 microvolt
or better) sensitivity at all the points I measured.  Transmit was
136-179.995 and 400-511 with power dropping off at the ends but still
usable (about 0.5w on the high scale at the band edges).

As usual, I take no responsibility for the mods, or your use of the unit
after mod.  Please exercise good judgement and don't endanger our ham bands
with your irresponsible actions.

The observations noted are all I tried and I have no further data.
This is such a delicate operation that one shot was all I wanted to do,
and when it worked I quit!!!

WARNING-CAUTION-LOOKOUT-ETC!!!
The diodes to be moved are microscopic!!  About 1mm long by 0.5mm wide.
This mod should be done by professionals on a closed track only.
Children, do not attempt this at home.  Requires extremely small soldering
tools and MUCH skill.  I had a professional surface mount facility do mine...


1. Open the unit by removing three screws from the back and one under the
   DC power input cover.  Carefully separate the front and back pieces.
   The two case halves may be disconnected by pulling the wired plug and by
   prying the brown latch on the ribbon cable connector up enough to
   release it.

2. On the front PC board in the lower right corner as viewed from the rear
   with the knobs pointing up there are seven spots for diodes in a row,
   with one diode missing.

                                    |
                     o o o o x o o  |
                    ________________|
                     2 3 4 5 6 7 8

   The numbers are D302-D308, left to right, with D306 missing.

3. Remove D304, and D307. Put them away in a safe place (Just in case...)_

4. You should now have:
                                    |
                     o o x o x x o  |
                    ________________|
                     2 3 4 5 6 7 8

5. Reassemble and good Luck.

Enjoy, but don't create problems with the new capability...Wouldn't it be
nice if Kenwood would make a RX only mod with these capabilities and we
wouldn't have to worry about accidental transmissions where we shouldn't
be transmitting.   I, for one, don't want or need to TX, just RX...

73, Cole, AA7RD
August 11, 1994

(Note - This mod also adds 2 more menu settings. One of which is an
        AM/FM demod selector for the 300-400 Mhz band. To access this
        band, select the VHF band, press F, then press the Low/Hi key.
        Repeat to return to 144 Mhz. The AM/FM selector will allow you
        to listen to Military transmissions in the 300Mhz band in
        either AM or FM.
        - Clayton)

++++++++++++++++++++++++++++++++++++++++++++++++++++++++++++++++++++++
V. Remote Base Operation with Kenwood 732/733
++++++++++++++++++++++++++++++++++++++++++++++++++++++++++++++++++++++

Kenwood has now simplified remote base operation of their mobile rigs
with the TH79.

I will not give a step by step on how to control the mobile rigs, since
they are different. Hoewever, to really understand this feature, I would
first get to know the remote control feature on the mobile very well. This
makes the following explanation a little clearer!

To access this feature, hold [PTT] and [MR] while [POWER ON].

The display will indicate -RC-, which I presume means 'Remote Control'.

If you have correctly matched your DTSS codes, frequencies, etc, the
dual bander's keypad now becomes a function pad. Pressing certain keys
enables or disables functions on the mobile rig by sending the DTMF
sequences for you.

Please note that all this fuction does is send the DTMF tones over the air
to control your mobile rig. I have not made a list of what each key does,
but as the 79 sends the DTMF tones, the display will indicate the function.
(i.e. - RPT ON, RPT OFF, TONE ON, TONE OFF, etc.)

73 de Clayton
KD4IDN

And this from Chuck Scott, N8DNX...

"The "RC" function is configured to directly control radios such as
the TM-732.  In fact, if you look at the layout of the microphone remote
commands for the 732 it very closely matches the key assignments for of
the "RC" mode.  Since I have a TM-732 installed in my car, I had a chance
to try this out and it's VERY convenient.  Everything from direct frequency
entry with the "F" key to enabling X-Band repeat.  I'm really surprised
they aren't marketing this feature of the radio."


++++++++++++++++++++++++++++++++++++++++++++++++++++++++++++++++++++++
VI. Post Modification Spec Sheet, by Clayton Wagar, KD4IDN
++++++++++++++++++++++++++++++++++++++++++++++++++++++++++++++++++++++

Here is a small chart showing the measured specifictions of TH79
S/N 60300272 after modification. The measurements were made with an
IFR 1200S Service Monitor, on the bench, with a 6V power supply.
Your milage may vary - these are just what happened with mine, and
I would suspect that most units are pretty similar.

73 de Clayton
KD4IDN


Band - VHF -----------------------------------------------------
Frequency       Sens (uV)       Power           Mode
---------       ---------       -----           ----
108             4               -               A3
110             2               -               "
115             .75             -               "
120             .40             -               "
125             .30             -               "
130             .30             -               "
135             .30             -               "
140             .12             2.9             F3
145             .12             2.9             "
150             .13             2.8             "
155             .15             2.4             "
160             .18             1.9             "
165             .20             1.45            "
170             .21             1.10            "
175             .30             0.85            "
179.995         .35             0.70            "


Band - VHF (2) (set to 300Mhz) --------------------------------
Frequency       Sens (uV)       Power           Mode
---------       ---------       -----           ----
300             50/75           -               A3/F3
320             4/20            -                 "
340             .3/.6           -                 "
360             .2/.5           -                 "
380             .2/.6           -                 "
400             .2/.75          -                 "


Band - UHF -----------------------------------------------------
Frequency       Sens (uV)       Power           Mode
---------       ---------       -----           ----
400             11              1.0             F3
410             4               1.5             "
420             1               1.85            "
430             .2              2.2             "
435             .12             2.3             "
440             .10             2.5             "
445             .10             2.5             "
450             .10             2.5             "
455             .15             2.3             "
460             .16             2.3             "
465             .20             2.0             "
470             .45             1.8             "
480             1               1.6             "
490             2               1.3             "
500             6               1.1             "
510             no RX over 509  0.8             "


++++++++++++++++++++++++++++++++++++++++++++++++++++++++++++++++++++++
VII. Cross Band Repeat, from Chuck Scott, N8DNX
++++++++++++++++++++++++++++++++++++++++++++++++++++++++++++++++++++++

  The TH-79 does go into X-Band repeat.  Press the "F" key then the "MONI"
key to enter repeat mode.  Use the same to return to normal.  There is a
10 min transmit limit so it's not useable for long duration monitoring of
a continuous transmission.  That's understandable in light of the number
of horror stories I've heard of people frying their HT's in repeat mode.

++++++++++++++++++++++++++++++++++++++++++++++++++++++++++++++++++++++
VIII. Other Observations, Ramblings, Etc.
++++++++++++++++++++++++++++++++++++++++++++++++++++++++++++++++++++++

From Chuck Scott, N8DNX....

  "Regarding the lack of a memory Lock Out function, I talked at length
with the Kenwood people.  They have been inundated calls about this and
have told me that they are preasuring Japan to come up with a processor
replacement to fix this, perhaps as a retrofit.  I encourage any owner of
a TH-79 to write to Kenwood insisting on such a modification at no cost
and asking that they be informed when it is available.  I think this is
justified for several reasons.  First, I have been told by another ham
that the official brochure indicates that such a feature is included.
Second, and more important, it is arguable that the radio is not suited
to the application without memory lockout.  After all, it's an 80 channel
radio.  To make effective use of that many channels REQUIRES a channel
lockout function.  Without effective use of that many channels, the radio
is not comparable to the current standard for such a unit.

  BTW, close inspection of the RF deck in my radio shows no obvious
missing parts.  I didn't remove the board to check the other side, but
my suspicion is that the 800 MHz parts are installed.  I'd be interested
in input from others on that.  So far I've not discovered how to make it
display any 800 MHz frequencies though."

=======================================================================
Kenwood TH79 Dual Bander Modification and Feature Guide  r1.5 The End!
=======================================================================

Date: Wed, 4 Jun 1997 23:16:03 -0600 (MDT)
From: Zoltan Kovacs <[e-mail]>

I would like to inform you about the modification on my TH-79A handheld
according to the information you sent me.

I had an outfit complete the modification - they charged me one hours labour.

Here is what the end result was after they removed dioides D304 and D307

        VHF Coverage:  Receive and transmit = 136.00 to 173.00 Mhz

        UHF Coverage:  Receive and transmit = 410.00 to 469.00 Mhz

I was surprised to find out that I lost the extended AM receive coverage,
that is the 118.00 - 135.99 Mhz coverage.

My frequency transmit range is quite different than that described in the
information you sent me.  Anyhow, I am pleased that I have extended UHF
receive coverage.

I would like to share a trick.  For those that are paranoid in
accidentally trasmitting outside the Ham bands, this can be overcome by
setting the frequencies in the Programmable VHF and UHF frequencies using
the Menu function.

Furthermore, if you would have any information on a memory lockout
function on the TH-79A I would be very much appreciated.

Thankfully Yours,

Zoltan Kovacs.

VE6ZOL.

--------------------------------------------------------
|
| This is the mod for the Kenwood TH-79a to open up the RX. I have performed
| this mod on mine and it works as advertised.
|
|
|                         WARNING!!!!!!!!!!!!!!!!!!!!!
|
| The part you will have to remove is VERYsmall!! Use a grounded soldering iron
| and keep in mind...If you don`t think you can safely do this mod, DON`T!
| Remember...You break it, don`t blame me. I warned you. All other usual
| disclaimers apply. Here goes.
|
|
|
| 1. Turn off the power.
|
| 2. Remove the three No.0 phillips head screws from the rear of the radio and
| the one No.0 phillips head screw from the side of the transceiver under the
| External Speaker-Microphone/DC Power jack rubber cover.
|
| 3. Remove the CTCSS unit access plate.
|
| 4. Carefully release the bottom of the front panel by squeezing gently on the
| sides, at the point where the battery inserts, to release the two hooks from
| the rear panel.
|
| 5. Gently separate the two halves of the transceiver using care not to damage
| any of the connecting wires.
|
| 6. Remove diode D307 from the circuit board mounted to the rear of the front
| panel. There are Eight vertically mounted diodes on this board at the lower
| right hand corner ( top of radio facing away from you). Note: D306 not
| installed from factory. Remove next one to the right.
|
|
|
|
|                              x     x     x     x     x     o     x     x
|                               |      |      |      |      |      |      |
|  |
|                              R     D     D    D     D    D     D    D
|                              E     3      3     3     3     3     3     3
|                              S     0      0     0     0     0     0     0
|                              I     2      3     4     5     6     7     8
|                              S
|                              T
|                              O
|                              R
|
|           X= installed     O= not installed
|
| 7. Reassemble the radio by reversing steps 1-4.
|
| Reset the microprocesssor by holding the [F] key depressed while the power is
| turned on. Then press the [F] key again at the "All Reset" prompt. (mine did
| it automatically).
|
| On my radio (S/N above 804xxxxx), this mod opened the RX ONLY. Others may
| open TX as well. DON`T transmit outside Amateur bands! Mr. Hollingsworth WILL
| get you!!!!!
|
| After mod you will have: VHF- 118-173.995 mhz & 300-399.990 mhz RX ( press
| [F] then hi/low/exlow power button for 300mhz rx, again to go back)
|                                   UHF-410-469.995 mhz RX.
|
| Also get two added MENU items: 19- FM/AM Mode     20-Program VFO 300-399
|
| Enjoy!!
|
|