ICOM IC-375A 220-MHz Multimode Transceiver
Manufactured: Japan (Discontinued)
It's finally happened. AM diehard 220 enthusiasts can now rejoice and revel in ICOM's latest entry into the VHF/UHF multimode market: The IC-375A transceiver. It's made exclusive* ly for the North American amateur market.
Similar in design and operation to the IC-275 and IC-475, this radio offers a wealth of features for everyone, from the casual FM operator to hard-core packeteers. Considering this is the first time any company has manufactured such a transceiver, one has to be impressed with the sophistication of the design.
The front panel. Note the virtually identical copy of its sister transceivers for 2m and 70cm. The bright, backlit amber LCD display jumps out, showing frequency, VFOt memory channel, RIT, tone squelch, duplex offset, and mode. The frequency selection dial sits beneath the display, and has silky-smooth operation over a variety of tuning increments.
The 375 has four modes: FM. LSB, USB and CW, Pushing the CW mode switch again enables the optional CW filter (500 Hz)r which the operator can use in conjunction with the Passband Tuning (PBT) and Notch controls for enhanced selectivity Provision is made to switch a tower-mounted preamplifier from the front panel (maximum power: 100 watts) as well as to enable a built-in speech compressor. There are also two speeds of AGC selection.
The user can select sub-tone frequencies on both receive and transmit, and store any combination of offsets, sub-tones, modes and frequencies in 99 seperate memory channels—more than adequate for everyday use. Two priority channels are also available which store similar data.
RIT (Receiver Incremental Tuning) is standard and permits a shift of up to 9.9 kHz either side of the displayed frequency. The RIT can be cleared to zero offset at the touch of a button. This feature works in all modes, including FM.
Additional controls set up the microphone gain (not deviation), RF output power, RF gain, CW keying delay, meter display, and AF tone quality from the built-in speaker. The AF gain and squelch controls are located to the right ol the display meter, directly below the main power switch, in order not to confuse them with any other controls.
Several scan rates are available. The standard band scan is incorporated, along with programmable range scanning, se~ lectable mode scanning through memories, and general purpose memory scanning A skip button allows the operator to lock out undesired channels when in scan mode. When using the programmable scan function, transmitting or touching the main tuning dial erases the preprogrammed band limits.
As on all new ICOM muftimod-es. the 375 has full break-in keying (QSK). Current activity levels are presently too low for QSK to be really useful now. In many cases also, full break-in keying isn't usable due to sequenced switching of amplifiers and external preamplifiers. The optional AG-30 mast-mounted preamplifier won't function when full QSK is selected either Semi break-in is also available with the drop-out delay set from the front panel. Note that no VOX operation is available—none of the new 75 series transceivers offer it.
The DATA switch on the 275 and 475 is also available here. ICOM claims a switching time of less than 5 milliseconds, which should be ideal for packet operation. Packeteers will not be able to use an external amplifier or preamplifier, however, due to this rapid switch time. The IC-375 also runs AMTOR. conventional AFSK RTTY, and SSTV.
A small insert with the IC-375A tells of the availability of the ICOM CIS (Communication Interface System), permitting control of these radios through a personal computer and RS-232 port. Such control permits displaying and operating the frequency, mode, memory selection and scanning functions, among others. ICOM doesn't say, however, what software is available to do the job. so look for it in the next few months.
The rear panel also has many controls. In addition to the CW keying speed, the user can adjust the tone of hts transmitted audio (brilliant!) and set the degree of compression in the speech processor. The remote connection for the RS-232 interface is here, as well as two accessory jacks for the ICOM AOS automatic squelch system and ALC control/external keying/receiver output.
The operator can also monitor his SWR via a three-way switch on the rear panel as well as power output. Connections for a CW key and external speaker are found here using 2 5mm mimplugs, and the CW sidetone level is accessible here. The antenna connector of choice is the SO-239 "UHF" socket, which is pretty much standard on 220 equipment. Although the 1C-375A comes with a built-in AC supply, the user can also access the 13.8 volt input directly for portable use with the supplied DC power cable.
I've had the IC-375 in my station for quite a few months now, and gave it a fairly hard run during the September VHF QSO Party. Over 50 stations were worked from this location using the IC-375A, a Mirage C1012 amplifier, and a single Cushcraft 220 Boomer at 60 feet Most of my operation was on SSB and CW (I use primarily an IC-37 for FM work), and the transceiver performed flawlessly the entire weekend. I had to stop operating and switch feedlines on 220 halfway through the contest due to an extremely high SWR condition that apparently made difference to the 375A.
CW was the main mode that weekend due to the generally terrible conditions and weak signals. I preferred the semi break-in mode and use a special eight-pm DIN to RCA plug cable to switch the C1012. The 375A, by the
way, keys an external amplifier by pulling it to ground, which is fairly standard practice. The eight-pin plug is similar to the one used by Kenwood. Since there was no available AG-30 preamplifier, I used the preamplifier in the Mirage with minimal results. The front-end sensitivity of the 375A is such that a preamp isn't needed most of the time. However, the S-meter is just as "dead" as on the 275 and 475, as the reader will soon see in the test data.
In practice, I set the AF Tone control at about 10 o'clock to eliminate a high-frequency hiss present with no signals and the squelch open. The speech compressor didn't seem to make much difference on distant contacts. It took as many tries to work weak stations with compression on as it did with compression off.
The RIT control is a real help on 220. especially with ail the older stations that drift out of the passband.
I used the Programmable Scan to set up limits of 220.080-220.150 MHz so that the radio was always seeking out new stations white I was on other bands. Most of the activity on 220 SSB or CW occurs during the activity hours at 0800Z and 2000Z with the band fairly quiet otherwise. Using this scan feature allows the contester to keep an extra "ear" on the band in case of an opening or a new grid square.
Received signal reports were favorable regarding the cnspness of the audio as well as clarity. Based on these reports, I set the mic gain control at 12 o'clock and left it there permanently. The supplied microphone is the ICOM HM-12 scanning type, allowing remote up/down selection of frequency. Serious contesters may wish to go with the optional SM-8 base station microphone and a footswitch, leaving the hands free for logging and tuning. (ICOM also makes the SM-10 microphone with a graphic equalizer and speech compressor.)
The following measurements were taken with an HP608F generator. Boonton 92 millivoltmeter and Bird 43 wattmeter. Power source was the internal AC supply. Take note, however, of two points.
- The IC-375A transmits across the entire specified range, but power output falls off significantly outside 220-225 MHz,
- Receiver compression point was significantly lower than on similar IC-275A and IC-475A models. See the sidebar.
The IC-375A represents a significant step forward in 220 MHz technology. There is no other comparable product that exists today. ICOM has built every possible feature into this transceiver to cover the wide range of opera1 lions and modes on 220 MHz. Its output power is sufficient to drive both solid-state and ground-grid tube amplifiers, such as the 8877 and 3CX800, to near the legal limit.
The front-end performance of this particular unit, however is not on a par with the IC-275A and IC-475A, It took considerably less signal to drive the front end into compression, and this might mean some noticeable intermod products during contest operation, or when strong adjacent channel signals are present such as television channels 12 or 13.
I noticed a slight amount of AGC ' pumping1' during contest operation when other strong signals were present, but it didn't degrade front-end sensitivity that much. The external preamp might make this Situation worse depending on its particular compression characteristics. Indeed, switching my external JFET preamp inline during crowded band conditions did just that.
Still, for the serious UHF operator, the IC-375A is a great way to go for multimode operations The overall design and performance combined with ease of operation makes this an excellent choice of transceiver - 73 Amateur Radio Pete Putman KT2B -