

@SUBJECT:Kenwood TH79 Mod File r.10                                  N
@FROM   :wagarbc@mail.auburn.edu                                     N
@MSGID  :<Cuwqyr.KzE@mail.auburn.edu>                                N
From: wagarbc@mail.auburn.edu (B. Clayton Wagar)
Newsgroups: rec.radio.amateur.equipment
Subject: Kenwood TH79 Mod File r.10
Keywords: Kenwood TH79 Mod Modification Feature
Message-ID: <Cuwqyr.KzE@mail.auburn.edu>
Date: Sun, 21 Aug 1994 23:08:50 GMT
This article split by uuPCB: Part # 2 of 3

From: wagarbc@mail.auburn.edu (B. Clayton Wagar)
Newsgroups: rec.radio.amateur.equipment
Subject: Kenwood TH79 Mod File r.10
Keywords: Kenwood TH79 Mod Modification Feature
Message-ID: <Cuwqyr.KzE@mail.auburn.edu>
Date: Sun, 21 Aug 1994 23:08:50 GMT


Kenwood TH79 Dual Bander Modification and Feature Guide  r1.0  8/21/94
=======================================================================
by 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. 

Most of these are borrowed from other operators, to whom we all owe thanks
for spreading information. I personally want everyone else to benefit from
what I've learned.

This is release 1.0 of this document, dated August 21, 1994.

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
yensid1@aol.com  (fastest, since I travel 5 days a week)
wagarbc@mail.auburn.edu (ok alternate)

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know of this mod, please write to me, even if you wish it not to be
published.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!

* Mods have not come from a Kenwood source, just experimentation by owners.


Hope you find all of this information useful. Again, please send corrections
or additions to yensid1@aol.com or wagarbc@mail.auburn.edu.

73 de Clayton
KD4IDN


+++++++++++++++++++++++++++++++++++++++++++++++++++++++++++++++++++++++
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.

PERFORMANCE. I was impressed, without a doubt. The '79's
sensitivity is markedly better than the 78, in both bands and
especially in the extended portions of VHF. And, spurious signal
(intermod) rejection seemed to be much better as well in the
side-by-side tests.

The stock antenna, however, was awful. I bought an ANLI 5"
dual-band flexi and it made a huge difference - signals just
breaking squelch with the stock duck were full-scale with the
ANLI.

Audio is fairly good for something so small. The quality was
marginally better than the 78 and tended to distort less at max
volume settings. Audio power would be stretched to use it, say,
with the car window open going freeway speeds.

Having loaned my wattmeter to a friend, I wasn't able to get
transmitter measurements to confirm power ratings. Reports from
those on the receiving end have been favorable so far, though.

ADVANTAGES. As mentioned previously, the 79's receiver quality is
significantly better than the 78, in both sensitivity and
intermod rejection. Battery life - even with the smaller
batteries - is supposed to be drastically improved due to a
number of design changes, particularly in the transmitter finals.
Have not been able to confirm that. And then there's the size.

DISADVANTAGES. There are, unfortunately, a few. One thing that
jumped-out very early was that there is no facility to "lock out"
a channel from the memory scan. If you select memory scan (hold
[MR] for 1 second), you get every channel programmed in the band
active for that "side", whether you want it or not. IMO, this was
a grave over sight on Kenwood's part. If someone knows how to do
this or there is a "hidden" lockout function, please post it,
because nothing in the manual even hints at being able to do
this.

Another disadvantage, albeit minor, is that there are no clocks
or timers. I normally eschew these gimmicks, but "on the road"
I've made use of the timer feature in the 78 as an alarm clock.
I'll miss it a little.

It has no 800 MHz receive, which the first two generations of
TH-78 has. This isn't a hard disadvantage, because the current
TH-78 has 800 MHz missing, too. I only mention this for current
78 owners who have pre-4/94 units.
066506032    243549
And, so far it seems that there are fewer "hidden" features
available, like cross-band repeat. I said "so far". There appears
to be no extended F-key function activated by holding down the F
key for 1 second; most of those feature selections are covered by
the menu display. But there's more exploring to do and we might
just bump into something interesting in the next few days -
"power on" has significance in one important command (memory
channel clear), so it may be important in switching other modes.

MODIFIABILITY. I studied the schematics (supplied) for the usual
strap selections for extended range and different markets. Yes,
they are there. When the opportunity permits I will
cross-reference the mod codes against other Kenwood schematics
and determine where the range extensions are. HOWEVER, there is
very clear allusion to an 800 MHz receive feature, and checking
the component list for the U.S. version codes, it appears that
*all* of the 800 MHz components are missing. Kenwood is meeting
the "no cellular" requirement purely by eliminating the 800 MHz
receive section altogether. So, technically, you would probably
be able to mod it for 800 MHz receive, but getting all of the
right parts (about 40 or 50 surface mount components) and getting
them to work without destroying something borders on improbable.

Overall, I like it, though I'm really hacked by the lack of scan
memory lockout - they *REALLY* messed-up by not including it.
...mm

P.S. After another day with the TH-79, I'm bumping my head
against more limitations.

Another feature lost from the TH-78: special scans. With the
TH-78, it was possible to have a variety of special scan
conditions. One of my favorites was to load a freq into the
"call" channel, and by holding [CALL] for one second it would
flip back and forth between two freqs. I used this a lot, and it
just isn't there on the 79.

Also, I spent some time trying various power-on key combinations
and found absolutely nothing. One thing for sure - if it isn't in
the manual, it isn't likely to be discovered accidentally.

The more I "explore" this rig, the more I get the impression that
feature selection may be "back to basics". Kenwood might be a
little sore after the TS-50 experience with the FCC and may feel
the need to make access to "tweaks" a little less obvious.



+++++++++++++++++++++++++++++++++++++++++++++++++++++++++++++++++++++++
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.

If I read the schematic right, the green wire corresponds to
"W301", which also serves the same purpose as removing "D308".
More research needs to be done on other mods; I'm especially
interested in extending UHF receive beyond 450.

There is a row of diodes right below the uC which appear to be
D302 through D308, the configuration straps. HOWEVER - I need to
caution anybody thinking about playing with the diode straps that
it will not be a casual operation. For one thing, the diodes are
SMD "603" style - extra, extra tiny - and the plastic board
hold-downs molded into the front case are right on the landings
for most of the diodes. This means that the board will have to be
removed from the case (a very involved procedure), and working
with the tiny diodes *will* require magnification tools as well
as the correct micro-tip iron. It is not a job for the
inexperienced or all-thumbs.

Also, as noted previously, the non-US versions of the TH-79 have
an 800 MHz receive section. All RF components of this section are
not present in the US version. Frankly, it would easier to import
a gray-market version of the radio than it would be to attempt
restoring this coverage in the US with parts.


+++++++++++++++++++++++++++++++++++++++++++++++++++++++++++++++++++++++  
"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)

++++++++++++++++++++++++++++++++++++++++++++++++++++++++++++++++++++++
Remote Base Operation with Kenwood 732/(733?), Clayton Wagar KD4IDN
++++++++++++++++++++++++++++++++++++++++++++++++++++++++++++++++++++++

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


++++++++++++++++++++++++++++++++++++++++++++++++++++++++++++++++++++++
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.

Since everyone else has 2 cents about extended transmit, here's mine...
I think that everyone should have the right to modify their equipment
to suit their desires, within the law. However, as someone who has 
exercised that right, I also think that those who use that capability
maliciously should be hung from the highest tree... ;)

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             "

=======================================================================
Kenwood TH79 Dual Bander Modification and Feature Guide  r1.0 The End!
=======================================================================


                   
