Adam, VA7OJ/AB4OJ's IC-756Pro III User Review
Icom ic-756 pro 3 transceiver in excellent condition. Fully functional, works and looks great. It has a few light surface marks, but they are hard to see, and has a late serial number (3205866) this radio has been well cared for in smoke free / pet free home. RADIOHF - Icom pro 3 Look to trade for icom 756 pro 3 for tentec orion 2 in excellent 3 has all filters anttena tuner 565 receiver factory install 6 meter transverter Manuel's shipped in original box this radio fully functional all bands to trade for icom756 pro 3 radio plus $500 different sell radio for 1200 plus 50 shipping. ICOM 756 ProIII Specifications. ICOM 756 ProIII Specifications Discontinued Amateur HF Transceivers. Number of memory channels: 101 (99 regular, 2 scan edges).
Initial observations (July 2005)
On June 30, I picked up my new IC-756Pro3 (S/N 32025XX) at a local dealer. That evening, I installed the Pro3 in my station. Preliminary findings are that it pulls weak, noisy signals out of the noise somewhat better than the Pro2. I was able to work a number of SSB stations on 40m which I would not have heard on the Pro2. The NR and NB appear to have been significantly improved. Overall, I would judge that the S/N ratio is better than on the Pro2, even in the presence of power-line noise. I find myself routinely operating with the preamp off; on the Pro2, I invariably had Preamp 1 on.
The next day, I was able to sustain the sked with my friend Matt KK5DR somewhat longer, as the Pro3 'hears' signals buried in the noise somewhat better than the Pro2 did. I am able (by using a combination of NR, NB, Twin PBT and Manual Notch) to squeeze intelligible copy out of the assorted 'garbage' on the band more effectively than on the Pro2. In addition, the Pro3's strong-signal behaviour appeared to be excellent. S9 + 60 dB signals 1 to 2 kHz above and below our channel edges did not produce any perceptible artefacts in the received audio.
When switched in, Preamps 1 and 2 do not raise the audible noise level in the receiver as much as they did in the Pro2. In the Pro3, the preamps have been designed for highly linear large-signal handling, consistent with a low noise figure. Preamp 1 has negative feedback to improve linearity without compromising NF. There has also been a significant gain redistribution. The first mixer has lower gain, with the result that the scope module in the Pro3 has its ownRF amplifier to bring up the vertical sensitivity of the scope.
Notes on ALC
The ALC is a little less sensitive; I need to set the Quadra ALC menu to 5 bars for 1kW output, vs. 4 bars for the Pro2.
As is the case for all other Icom HF transceivers, the rear-panel ALC jack is compatible with a negative-going ALC voltage in the range 0 to -4V.Positive voltage shouldnever be applied to the ALC jack.
In August 2007, I performed an ALC overshoot test on my Pro3/Quadra station.Here is the test report.
There have been some improvements in operational convenience. The mini-scope is great - you can now display 3 windows; frequency/mode etc., mini-scope and bar-graph meter, filter menu or any other lower window that used to suppress the scope on the Pro2. There are two clock displays - UTC and local - and a simple screen-saver which displays the owner's callsign moving about on a black background. By being able to leave the bar-graph meter on-screen along with the scope, I learned that compression peaks at 6 to 7 dB when it only shows 2 to 3 dB on the much slower moving-coil meter.
Display quality
I have the impression that the Pro3's TFT display is superior to that of the Pro2. The screen image is brighter and a little sharper, the contrast is much better and the colours are more saturated.
A few measurements
As the ARRL, RSGB and others have already subjected the Pro3 to exhaustive test suites, I felt that any such effort on my part would be redundant (apart from the fact that my second signal generator is much too 'dirty' for meaningful RF 2-tone measurements!)
To satisfy my own curiosity, though, I ran a few quick receiver tests: MDS, reciprocal mixing noise and filter shape factors. The test setup was as follows:
HP8640B signal generator, calibrated against R&S URV4-03 RF power meter with 0 dB probe; Sinadder 3 configured as true RMS audio voltmeter connected to [SPKR] jack. NB off, NR off, ATT = 0 dB, AGC MID. Offset tone pitch = 1 kHz (SSB), 600 Hz (CW). SSB and CW 'Sharp' filter shapes selected.
1: MDS (Minimum Discernible Signal). In this test, MDS is defined as the RF input power which yields 3 dB unweighted S/N at the output. The results obtained are very close to those in Ref.2.
MDS at 14.1 MHz (dBm) | ||
---|---|---|
Preamp | SSB 2.4 kHz | CW 500 Hz BPF |
Off | -126 | -131 |
1 | -133 | -139 |
2 | -135.5 | -142 |
2: Reciprocal Mixing Noise. Reciprocal mixing occurs in a superheterodyne receiver when the noise sidebands of the local oscillator (LO) mix with strong signals close in frequency to the wanted signal, producing unwanted noise products at the intermediate frequency and degrading the receiver sensitivity. Reciprocal mixing noise is a measure of LO spectral purity.
In this test, a strong 'undesired' signal is injected into the receiver's RF input at a fixed offset from the operating frequency. The RF input power is increased until the receiver noise floor increases by 3 dB. The reciprocal mixing noise parameter, expressed as a figure of merit, is the difference between this RF input power and measured MDS. The test is run with the 2.4 kHz SSB filter selected, and preamp off. The higher the value, the better.