Subject: Kenwood TH79 Dual Bander Modifications 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 yensid1@aol.com 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 If you know of this mod, please write to me, even if you wish it not to be published.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 yensid1@aol.com 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! =======================================================================