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Author Topic: IC-7100 VS FT857D for portable operations  (Read 4059 times)

Posts: 5329


« Reply #15 on: October 19, 2017, 08:49:40 PM »

the side by side test using the web SDRs is a fair enough real world test. Same antenna, same tuner, same receiving station, switching back and forth many times in a short period of time.

But, not necessarily the same source conditions.  You have no idea the degree of compression, audio frequency response and even spurious emissions the two units had.  Sure, one is "stronger" but it may not be "better".  Your setup cannot adquately quantify that.

I wouldn't say that I have "come to a presumed conclusion using a test set up that is inherently incapable".

Whether you say it or not, you don't.  Unless you "scream into the mic" with a perfect sine wave, an averaging meter won't tell you enough about the modulation to make any useful conclusions.

It is only putting out 40 or so watts average on SSB, screaming into the mic.
That is with RF power at 100% and mic gain at 100%.

I've never seen a radio, ever, that required "screaming" at "100%" to achieve full power.  This may be a case where the 7100's ALC is adequately throttling back the gain, where the 991's is not and is blowing junk all over the band.  There's no way to tell just watching incident power.  One thing is for sure, if your 991 is putting out 80W with voice in SSB, it's being overdriven like crazy.   Average voice power for SSB is somewhere between 25-40%.  Even less if you operate below the ALC range.

If we all had to have lab grade equipment to form a conclusion most of us would have to give up and never try to figure anything out.

Using a PC to generate known tones and levels could go a long way to creating a repeatable and consistent test setup.  Our predacessors didn't have those, but most hams these days do. 

I get you're trying to do an A/B comparison, and you're observing a difference.  I'm just pointing out that the reason for the difference you observe cannot be discerned by the way you're testing.  You're concluding the "weaker" radio has a problem or is in some way deficient.  I am saying that until you can be sure there aren't other factors such as compression, equalization or other variables that can influence the response you really don't know if it's bad or not.   

For your application what I'd be looking at isn't "talk power", but how well a radio operates both transmit and receive as the input voltage ramps down as your storage battery discharges.  So it's a given that the 7100 requires 13.8V for 100W output, but what happens when you're operating on a battery that starts at 12.78V and goes down from there?  And what would be the minimum level of output you would require over the discharge slope of the battery?   Or would you use a battery booster to mitigate that? 

Mark K5LXP
Albuquerque, NM


Posts: 115

« Reply #16 on: October 20, 2017, 07:47:10 AM »

Mark, you make some points. However, I wouldn't say I have made conclusions but rather observations.

The web SDR does indeed give you some *idea* of signal quality. As does the ear. It certainly can't give you hard numbers but it can give you a clue. So it isn't just a guess that there is a difference in strength and the 991 isn't achieving the stronger signal by blowing wide. Using a tone generator is a good idea, I'll try that.

As to the 991 "blowing junk all over the band" the web sdr gives me a solid indication that it doesn't. I will say (and I did earlier) that the 7100 looked a little cleaner. The 991 does indeed show about 50 ish watts when using it normally. The 7100 shows about 20.

Chewed the rag and compared the rigs with three friends yesterday afternoon on 40 meters, one in OR one in NV and one 20 miles from me. All said my audio was muddier and had more bass and my signal was a *little* weaker with the 7100. I'm sure I can tweak the audio on the 7100. This was done with RF out 100%, mic gain 50% and compression of 5.

And let's not forget that I am not by any means the only person to have noticed this. Icom put out a fix for it too.

As to input voltage, you nailed it! That is indeed the next series of tests. For mobile operation input voltage VS watts out is important. Sure wish I had a FT-857 to do all this side by side with. Anyway, I am going to start with dialing down the voltage on the power supply and see what happens to output. I suppose if necessary I could get a boost converter, but that is another wad of cash.

Again, I am still leaning towards the 7100. And the difference between the two rigs here is very small. After all, the difference between 50 and 100 watts is 1dB, barely perceptible. My concern is that portable antennas are usually not the most efficient and then the difference may be more telling.

Mark, thanks for all the time even if we aren't agreeing on everything. We all need our conclusions challenged. And I *was* wrong, once, a long time ago...  Roll Eyes

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