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Numbif 9 on your Feedback e*rtf
I COM has always had a sensible new^equtp-
ment pohcy: Never release a new rig until the lifespan of an older model is finished. This policy has probabiy saved the sanity and marriage of more than one operator because the cost of a new rig can be spread over several years before a new version hits the market.
Considering this, Ihen, you can; imagine my surprise when the improved JC-751A appeared in ads. superseding ihe current IC-751 as ICOM's to p-of-t he-line rig. After ali, the 751 was introduced about three years ago and seemed to still have some life left. So, you can also imagine my desire to get my hands on the newer version to see rf the rig has changed.
After using the 751A for an extended period, t can say that there are some changes. The 751A is built upon the technology of the 735 (revtewed in November, 1985) to create a virtually new rig
You really wouldn't think the 751A is a new ng from the outside because it looks just like the older 751. right down to the 35 knobs, control switches, and buttons on the front panel, it also has the same 105-dB dynamic range, continuous receive coverage through 30 MHz, rnultirnode (AM, FM, CW, and SSB) capability, nearly the same LED display (with a couple of additions), and 100 Watts of output power.
But. if you were to continue thinking tike that, you would be making a mistake. The new 751A has more in common with ICOM s other state-of-the-art rig, the 735, than it does with the Older 751. in fact, comparing the schematics shows that with the exception of a couple of integrated circuits, the 751A and 735 are just about the same. The key difference in circuitry is that the customized microprocessor in the 735 controls a multifaceted liquid cryslal display (LCD), while the 751A uses a multicolored light-emitting diode (LED) display.
Both radios take advantage of newly developed central processing units for control This means the 751A is highly versatile, like the 735. For example, the new CPU allows monitoring of all 32 memory channels or only those storing a particular mode—FM, for example. Further, the programmed scan feature allows scanning between any two programmed frequencies. In all cases, though, the auio-stop feature of the 751A hafts scanning untitaGSO has finished and then automatically resumes when the frequency is clear.
This is like the 735Ts capability. The chiet difference between the two is the fact that the
Numbif 9 on your Feedback e*rtf
751A has 32 memories and two vfo's, while the 735 has 12 memories and two vfo s. The 735 also has an internal fan and no heat sink, while the 751A has a huge heat sink and an external fan.
In fact, the 735's tan comes on after a short time of heavy use, while the fan in the 751A remains off. This is due to ihe size of the heat sink. Further, the 735"s fan is variable, meaning that the higher the demand, the higher the fan speed. This makes the 735's fan obtrusive at times in a quiet shack. The fan on the 751 A. on the other hand, is quiet and only comes on when needed In fact, it's barely noticeable under most circumstances.
To be fair, though, the real comparison should be with the older 751, the rig thai the 751A replaces The ikey difference between them is important—program storage. As for other specifications, they are pretty much the same. For example, the new 751 A's dynamic range is 105 dB, as is the 751+s. ^he power requirements are the same— 13.8 V dc: the usable temperature range is the same— 14 to 140 degrees F; the display resolution is the same—to 100 Hz; spurious emissions are down more than 60 dB. as well as having harmonics down more than 40 dB; sensitivity is better than 0.5 uV; and selectivity is better than 2.3 kHz for SSB, CWi and RTTY at -6 dB.
The specifications, then, match them well But, the two 751s are different. In the 75t, ICOM used dynamic random access memory (DRAM) to store program and frequency information. The DRAM was backed by a lithium battery, whose average life was figured at about frve years Once the battery died, the programming disappeared due to the loss ot power to the memory, and the rig had to be sent back to the factory for reprogramming. Just about all the older ICOM microprocessor-controiied models used this plan.
Evidently, ICOM has seen the tight because it now stares its programming in nonvolatile memory. The only voiatiEe memory is user memory, which contains the frequencies you've programmed as well as the modes. The Jithium battery now backs up this user scratchpad, it's quite an improvement and shows that ICOM is willing to listen to consumer input,
Looking at the 751A you wouldn't think anything has changed at all The reason, quite frankly, is that the boxes look alike. However, when you look dosety at the front panel, you begin to see some of the changes that have been implemented. For example, the 751A is an improved CW rig. It now sports an electronic QSK keyerthat is capable of up to 40.vpm It also has a standard 500-Hz CW filter and a CW sidetone monitor, so you can monitor your code in transmit and receive
Another improvement over the 75; is an added LED annunciator in the display The new annunciator indicates whether you re using the tuning dial or bandswitching functions The 751A also has smoother tuning. While the 751's tuning was goodr the 751 A's tuning is even better. It feete silkier and features a newly designed tuning knob.
Many of the improvements, however, are ' under the skin." For example, the new 751A is even more stable than the 751 thanks to a new Ihermal sensor that monitors internaE temperatures. The sensor automatically turns on the fan which, in turn, ensures that there's no thermal drift
Further, the new modef boasts a 9-MHz notch which drastically reduces QRM In fact, just using the passband tuning coniroi and the notch filter will be enough to knock out any QRM on a particular signal The 500Hz CW filter is fike icing on the cake. And. in some cases, i wonder if you reafly need the fitter.
Other worthwhile improvements over the 751 are a new age system, new compressor circuitry for better audio, and a new af gain control system, which improves control of CW sidetone volume.
With ail these improvements, though, there are a couple of important items to note on the CW keyer and the noise blanker. The CW keyer speed control is decidedly nonlinear, Like many analog meters, large changes in speed are crowded into small spaces on the dial, i his means that it's tough to lind precise speed control toward 40 wpnv Further, a I 40 wpm the weighting tends to become shaky and imprecise. The QSK feature is a nice addition, but for most operators it's probably overkill.
The 751A features a selectable noise blanker which eliminates all but the most stubborn wideband and narrowband noise. (I have a source near my house that's virtually impossible to eliminate, but the blanker managed to get a good chunk of it)
But, while it s a nice feature, it's not wiihout problems Ai its highest sellings, it causes CW stgnais to become distorted, almost keyclick-Jike in lone. It s something you should be aware of if you're planning to buy this radio. However, it isn't a major problem because most of the time you'll probabiy operate the noise blanker at a lower setting.
Overall, then, the 751A is a worthwhile improvement over the ofder 751. It corrects some of Ihe flaws that were readily apparent in the older version and improves upon the radio's already solid basic features.
If you're looking for a new HF rig thai combines general coverage ana multimode capability. look at the 751A You won't be disappointed. ■
144-MHz Antenna Test: Three For Two by Peur H. Puumm KT2B
Cushcraft 32-19 and 42-18XL Boomers Cushcraft Corporation PO Box 4680 Manchester NH 03108 Price Class: 32-19 $140
Tonna F9FT 17-Element Yagi
The PX Shack 52 Stonewyck Drive Belle Mead NJ 08502 Price Class: $120
Last year was a grand one for French and American relations, owing to the 100th anniversary of the Statue of Liberty. With that in mind, it seems entirely appropriate io review these products—the premier 144-MHz yagis from two of the best-known names in antennas here in the United States and in France.
Cushcraft Corporation of Manchester. New Hampshire, has long been known for (heir 32-19 19-element "Boomer," as it has come to be known. This is one of the most popular antennas in the world for weak-sig-nai work on 2 meters, and its popularity supports its performance and durability. Recently, Cushcraft introduced the 42-18XL 10-element yagi, using a 28-foot boom for that extra 1 d8 of gain, based on the 19-eiement version,
Antermes Tonna of Reims,, France, is no
Number 10 on your Feedback card stranger to the weak-signal world either! Many of the top operators in Europe employ ihear 17-element yagi stacked in H-frames for con-lest and EME work. Tonna has long been known for their innovative square booms and easy product assembly, and is now making inroads in the U S market The comparative figures for each antenna are listed in Table t. Note that gain figures are based on manufacturer's claims.
Representative models of these yagis were obtained off-the-shelf" for the purposes of this review Tne F9FT Tonna arrived about the same time UPS dropped two big boxes from New Hampshire on my doorstep, and I commenced with the project.
The F9FT Tonna comes with ihe various elements bundled together with tape
The boom sections (four of them) are marked with colored rape at the ends to aid in matching the correct boom sections quickly. On all Tonna antennas that l1ve used, one end of the boom has a red cap and the other a black cap This matches the boom brace as well.
As mentioned eartier, Tonna employs square boom material. This makes assembly much easier, as you simply snap the element into a molded plastic mount (the center of each element is marked with a crimp), then fasten the element to the boom with a wing screwand nut. The mount is channeled to fit securely to the boom, incidentally, all of the mounting hardware is separated into various bags. This is a big help as you don t need to sorl out all of the hardware you don't need at the moment to get to what you do need AH hardware is stainless steel except the boom-to-mast clamps, which are galvanized.
The driven element is pre-assembled and tested at the factory. It also fastens with one wing screw to the square boom. The trigon reflector assembly attaches with pre-thread-ed steel plates and wing screws. You really need only a 10mm wrench to assemble ihe whole thing, and Tonna includes 2 brackets to accommodate up to a 2" mast. One is also fitted snug to the square boom, and the other is attached to the brace Jncidentaify the
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