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Reviews For: Kenwood TR-7400A

Category: Transceivers: VHF/UHF+ Amateur Base/Mobile (non hand-held)

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Review Summary For : Kenwood TR-7400A
Reviews: 27MSRP: 399.00
Description:
Early Synthesized 2 Meter Mobile Rig
Product is not in production
More Info: http://www.universal-radio.com/catalog/fm_txvrs/tr7400a.html
# last 180 days Avg. Rating last 180 days Total reviews Avg. overall rating
00274.7
W8ZNX Rating: 2006-01-22
heavy duty Time Owned: more than 12 months.
Bought my TR-7400A new over 30 years ago
was driving tractor trailer for a living
this radio has over 1,000,000 hard truck miles
day in day out use for over 12 years on the road, in all kinds of wx and
and all kinds of tractors
some times changing truck every week
if one year of hauling steel
in a R model Mack with camel back suspension
could not shake it to pieces nothing can!

yes sometimes the digital read out would
stop working but just bang hard on the
top and it works

looks like it's been in a war
dented, banged up, paint wore off most
of the bottom and top

got more use out of this one radio
than any 4 other radios ive ever owned

dit dit Mac w8znx

AC5XP Rating: 2005-05-12
Classic VHF radio, built like a battleship Time Owned: 0 to 3 months.
By: Loek d'Hont AC5XP

The RT-7400A is a two-meter FM transceiver that stems from the early eighties. It covers 144MHz to 148 MHz. It was the successor of the Kenwood TR-7200 (sold in the US as the Drake TR-72) and competed with Yaesu’s FT-227R. It must have been one of the first synthesized VHF rigs that Kenwood has produced (the TR-7200 was a crystal controlled radio)

The first thing one notices when looking at this radio is the way the frequency is set, which is very basic indeed.
There is a control for each digit; one switch sets the MHz selection, one for 100 KHz, 10 KHz and a push button to toggle between 0 and 5 kHz. This might look primitive today but you have to look through 1980 glasses: This was a huge leap forward from the crystal-based radios, every frequency could be set with crystal stability without the need for additional crystals.

Subsequently, there are no memories. Repeater offset is done with a separate 3-position switch.
Because of this concept, at first glance the radio almost looks like a military radio. When one looks a bit deeper it turns out that there is a diecast front panel, aluminum machined knobs and an over-all feeling of robustness. All of which makes the military impression even stronger.

When one lifts the hood, the construction turns out to be superb. Everything is easily accessible and well organized inside the case. Wiring is kept to a minimum and neatly laid-down. The synthesizer section is easily recognized from the RF boards.
What catches one's eye is the 3-stage helical filter to keep the "out-of-band garbage" away from the mixer stage. That they don’t do any more in today's radios! Not only because it is too expensive, but also because we all wanted "general coverage" receivers for our ham radios, preferred is DC to daylight….

It always strikes me how much the Kenwood and Yaesu radios of the era look alike from the inside. Same construction techniques; same type of wiring and same component vendors. Even the way the synthesizer is separated from the main unit and done on FR-4 boards (where the RF boards are on phenolic boards) is identical. I'm almost sure the radios actually come from one and the same manufacturing company. Who knows.

Conceptually the radio is straightforward and offers little surprises. The master VFO is the synthesizer. The latter is built around the venerable MC4044 phase-frequency discriminator. I don't know who invented this circuit (it doesn't bear anyone's name) but whoever it was sure deserves a Nobel price, hi. The MC4044 is a difficult to get chip nowadays but the digital circuit is used in every VLSI synthesizer chip ever made.

The programmable dividers of the time did not like frequencies much higher than 10 MHz so a mixing scheme is used to mix the VHF VCO down to this frequency range against a fixed frequency from a crystal driven stage. The stage actually deploys 2 crystals which take care of the 0 and +5 kHz offset mentioned earlier. That also means the synthesizer's smallest step size only has to be 10 kHz, not 5 kHz.
The +600 and -600 kHz for repeater offset is actually created digitally (by offsetting the digital code for the programmable divider) which is unusual compared to contemporary radios. This was in fact the only surprise I could find in the design.

The RF section is straightforward; receiver starts with a dual-gate MOSFET RF stage and mixer, with the earlier mentioned helical filter in between the two. First IF is 10.7 MHz which passes first through a monolithic crystal filter and then through a 10.7 MHz ceramic filter. Then the signal is downmixed to 455 kHz where the "main" IF filtering is done through a solid ceramic filter. Limiter, discriminator and AF stages are all done discrete. Actually, apart from the synthesizer stage (which is built around TTL and CMOS off-the-shelf chips), there are very few ICs used in this radio. This is a big advantage if something goes defect; you won't have to start looking for an incredible difficult to find custom chip when parts need to be replaced. Everything is still available albeit a bit difficult for the earlier mentioned MC4044 chip.

The transmitter starts with a crystal-based 10.7 MHz oscillator which is FM modulated. This is than mixed against the synthesizer signal which yields the transmit frequency. The signal is amplified and filtered. The RF amplifier is quite beefy for the era; a hefty 25 watt is produced; contemporary VHF radios of the time were more in the 10 watt range.

How does the radio work? No complaints here. The receiver can compete with anything on the market today. Not once have I noticed an intermodulation product from paging towers (or maybe these towers are all turned off nowadays?), the helical filter seems to do its job. (FYI, the manual calls this a "Herical resonator", I have found the translation to be poor. In the area of manuals Yaesu was clearly superior.)

The transmitter has excellent modulation, and the 25 watt RF output can be burned over a prolonged time due to the heavy heatsink.
The frequency readout uses large 7-segment LED displays, even the first two fixed digits are shown (this is where Yaesu got cheap with the 227). One has no problem reading these. The S-meter is clear and bright. The controls have a logical lay-out and feel solid. People with thick fingers won't have a problem operating this radio, that's for sure.
On the back, there is a two-prong DC connector, the same as on the Yaesu FT-227R. But the polarity is reversed with that radio! It is a bit silly that the two manufacturers could not agree on harmonizing this. Furthermore there is the inevitable SO-239 "UHF" connector and a jack for an external speaker. On the side of the rig there is a connector for an (optional) external DTMF keyboard. On that note (no pun intended), the radio allows for optional PL tone filters to be installed but this would be impractical in today's repeater environment because you would only have a single, fixed set of PL tones. The latter is the only thing that prevents you from using this radio the way you would use a modern rig: No PL tones. One way to fix this would be to connect the radio to a switchable off-the-shelf tone generator via the DTMF connector, this should be very do-able because the connector also offers DC voltage available during transmit.

Another thing that is worth mentioning is the microphone. This is a very sleek and small unit with a nice working PTT switch and a large element (it is not an electret mike, although one might think so judging the over-all size).

To summarize, this is a very robust rig with excellent radio characteristics and equipped with no-nonsense controls. What I almost like the most on this rig is it’s "face": I really like the military look and feel. But in all fairness, all radios of that era were lookers. Maybe I’m getting old but today’s "organically shaped" radios just don’t do it for me.
Get yourself a TR-7400 – A great and classic collector's item!
KA4TWK Rating: 2005-02-26
+++Try a MC-50 Mic +++ Time Owned: more than 12 months.
I have had this unit for many many years. Don't even remember when I got it. The stock Microphone has never been an outstanding preformer. Fellow Hams have always said the stock mic made my voice sound tinny. I recently came across a used MC-50 Mic and have begun using it. It plugged right in with no modifications. The audio reports are now outstanding. I use the unit as a base rig and have the local tone board installed. Excellent rig and simple to use. With the MC-50 mic, it is even better. Bill ka4twk South Carolina
KE7ALG Rating: 2005-01-29
A tone unit can easly be added! Time Owned: more than 12 months.
This was my first 2meter radio and it was very to use I am curently selling it on ebay as I replaced it with a TM-261A. The TR-7400A is a very easy starter 2 meter rig! And tough!
I have added a SS-64 Encoder to this unit and it works very well. But I moved the SS-64 to a TR-7850. To check out this unit go to
http://www.com-spec.com/ss64.htm
Al
KD5LIZ Rating: 2004-07-30
good radio Time Owned: more than 12 months.
this is a wonderful radio it was my second radio i got it a few years ago and paid 40 bucks for it it all worked after rewireing a cobra mic and makeing a new set of power wires but i'm trying to figure out how to put in ctcss in to this good old radio but cant find any information on how to do it and would like some help if anyone has anyinformation would like to hear from you post on here
WD4SIK Rating: 2004-07-14
Sherman tank Time Owned: more than 12 months.
Excellent quality. With only 25W can punch and talk to repeaters 50+ miles away with a Cushcraft Ringer Ranger AXR-2 at 20 feet.

Had it since 1978 and still working flawlessly. Does not get much better!
AD7DB Rating: 2004-06-08
Good solid radio for what it does Time Owned: more than 12 months.
I bought this one used back in the mid 80s. This radio is indeed built like a tank. For a radio from the 1970s it sure had the features for its day. But, a lack of built in PL encode limits its use on many repeaters these days. I got mine for base station packet radio use, and the 25W transmitter really packed a punch. The TR relay goes CLINK-Clunk and would regularly wake me up at night if someone connected to my station or started digipeating! Overall it's a good radio for base use in that way, probably eats too much power to use it mobile for APRS except when the vehicle's running.
K5III Rating: 2003-10-16
Classic Tank Time Owned: more than 12 months.
Bought mine on eBay 2 years ago for $59. Has been used on several occasions. This is a somewhat heavy radio and built like a tank. It has relay switching. I have had good signal reports. It has not had any problems whatsoever. This is another one that Kenwood did right. Even though there is no PL, it is a tough well built radio with a military styling. I recommend this one.
KC0LOD Rating: 2003-05-14
Great radio Time Owned: 0 to 3 months.
I bought it at the Norfolk Hamfest 03. I use it in the house and It is easy to use and is nice and easy to see display. It is actually older than I am. Kenwood got it right, like they usually do.
KA7ZPW Rating: 2003-04-29
Like a Rock! Time Owned: more than 12 months.
My father bought one new in 1978, and other than having it realigned a couple of times, and replacing the microphone, this rig has never had ANY trouble whatsoever. It outlasted at least five cars that my dad used it mobile in. I use the rig now, in the shack, and though it won't do pl, it works for everything else. I miss the old familiar thunk of this rig's tr relay, when using newer rigs.