My quick trip to the San Antonio Ham store was mainly to pick up a roll of new coax cable, and look at gear in the "tail-gate sale". The tailgate was pretty good for a sweltering morning, and turnout was good. Much to my delight, the Ham store had an IC-7800 set up for demo. The unit was connected to a tri-band beam about 30 ft above the roof. The store is directly across from the San Antonio International Airport, and a major highway - a very RF noisy environment.
I sat down alone with the 7800 and these are some of my observations in the short time I had with it:
The receiver is pretty quiet, even in this harsh environment. I observed that going from Preamp Off to Preamp 1, there was about a 3dB increase in the noise floor, then another 3dB increase going to Preamp 2. Therefore, the use of the preamp does in fact increase the noise floor, but not as much as on other radios. Signals seem to increase by about 6 -10dB, disproportionate to the noise increase.
The main tuning encoder had an error; while tuning in a counter-clockwise direction; the unit would "lock up" tuning from time to time. It did not do this in the clockwise tuning direction. (The "lockup" would cause the display to stop updating, or to stagger back and forth on a given number). The owner of the Ham store told me that a good number of 7800s have had this same error. It could be a mechanical defect, or an electronic misalignment. I have gotten reports that a few encoders/shafts have been damaged in shipping too.
The band conditions were horrible on 20 meters this morning, but I tried to find a strong CW signal to test the 7800 for close-in signal handling. I found an S-9 CW signal, and using the standard 500Hz filter setting, I slowly tuned away from this signal (which was a little difficult with the encoder locking up every few turns). I noted that the S-9 signal was completely gone, with no artifacts at all, at 500Hz away from center frequency.
I checked the noise blanker, but the noise that was present was not affected at all by the NB, no matter what level or width settings I used. There was only about a 3dB decrease in overall noise floor with the NB engaged. Perhaps a noise with a wider pulse frequency would be more affected by the NB. However, the noise that was present was the wide-band AC line hash type.
I tested the Auto-Notch on a CW signal; it was extremely effective, with little or no RX desensing noted. I could not find the multi-tone signal that usually resides on 14.316MHz, (yes, prop was that bad) so I could not test the unit on this type of signal.
I noticed something about the spectrum scope display that I did not really like. The lowest resolution is ± 2.5 kHz, meaning that the entire screen is 5 kHz wide. The "grass" does not look like grass at all, it appears more like little round topped hills. The problem with this is that if a signal does not have at least twice the level of the "grass", it is nearly impossible to discern a signal from the noise, since both look the same on the screen.
I tried all the scan width settings and it only gets worse as you go wider, since the amplitude of the signals is reduced in proportion to the noise levels. Weak signals become harder and harder to see. I prefer the screen of the P2, where the "grass" looks like grass, or a row of "spikes", and SSB signals look like a pine-tree with a pointed top, CW signals look like a round top hat, and noise is a series of vertical lines or "spikes".
I know that the P2 does not have the narrow resolution bandwidth (RBW) of the 7800, but if a user can't discern what a signal is, and what is noise, it really does not matter, does it ?
Even looking as the scope of the 7800 on a 17" CRT monitor the ham store had connected, I saw the same thing. It is difficult to discern the desired signal from the noise when the signal amplitude is less than twice that of the "grass". Strong signals are easy, since they "stand out" far above the base-line noise level. The peak hold function can help in detecting and locating intermittent signals, but if the signal is not strong it could easily be lost in the "grass".
Craig is the owner of the Ham Store/Kcomm Inc. in San Antonio. I've known him for over 15 years, and currently own two radios I purchased from his store. Craig told me that he has sold four 7800's thus far at a price of $10800. Craig said that a few of the buyers were very old guys who can't see very well anymore, and had to use magnifying glasses to see their Pro series screens - but now with the large outboard monitors , they can see the display just fine. I can see that if a user is going to have a large CRT/flat-screen monitor connected, it might be good to have it located directly above the radio, so it can be seen easily while tuning the radio.
Here are some minor items I notice that differ from this "production" model, and the "prototype" we saw at Dayton 2003:
The knurled knob skirts that were silver on the prototype are anodized charcoal color on the production unit.
The deeply embossed ICOM logo on the production unit was not present on the prototype.
I did not have time to test and observe every subsystem of the unit, but I did look into the main items I would be concerned with in a receiver.
I hope you can use this report well in your contemplations on this radio.
Feel free to share this document with those who can use it.
73 de Matt KK5DR
Page created and edited by A. Farson VA7OJ/AB4OJ. Last revised: 02/06/2012