15 aprilie 2016

Playing with the front end of the IC-7300

I heard some rumors about how bad is the IC-7300 front-end and how unsuitable is for hunting low signals so I want to try to push the input to the limits.

So, I put a power splitter to the antenna input of the radio and feed it with two signal generators.
One set on the receiving frequency at -100dbm and one at various frequencies, set at 0dbm. You see, the difference between the signals is huge in terms of input signals...
I am not trying to say that this setup will produce the same result as in real life but is a base for some evaluation of the receiver.

Therefore, the receiving signal is at S1 (-100 dbm) and the perturbation will be at about S9+27 db, according to the IARU reccomandation for HF S-meters.

The radio was set to work with no preamp nor ATT, and the NR OFF.

At S1, the signal was full readable with some noise. With NR ON set at 5, the noise dissapeared and the receiving signal was full quiting the speaker!

When I was applying the perturbation outside the selected filter, OVF quick came on the LCD and the noise increased but the signal was still readable. The NR made the signal nice and clean, altough not so clean as the first time.

When playing with the perturbation signal inside the same filter's passband, the noise increased a little bit but not as I expected.

When the OVF was LIT, there was some artifacts on the waterfall.

The OVF and the artifacts was gone when I reduced the RF gain (instead of 12, the RF gain was set to 10).
The signal was still readable but with a price in noise level... The NR does it's job very well in reducing that noise.

By reducing the perturbation signal at -6 dbm, the OVF goes down and so did the WF artifacts.
At -12dbm, only a slight increase in the noise was there, nothing to upset me, even without the NR.

This beahviour was observed anywhere in the HF bands. I did not test yet the VHF (50+70 MHz).

Indeed, the out of band strong signals are able to put some noise in the receiving band but is not so bad as stated on some other places on the net.

However, the biggest problem is with the harmonics; I set the signal generator at 7.150 kHz at 0 dbm and I found a S9 signal on 14.300 kHz and a S8 on 21.450 kHz! This could be a problem when working on a crowded area (crowd of ham, of course).

A theoretical approach say that the best antenna for this radio will be a monobander or a non-resonant antenna tuned with a AH-4.

As a personal experience, I used the radio with a multiband vertical and find nothing to complain as the nearest ham is at about 8 km from me and there is a hill between us.

The test was long and complicated as I measured also the S/N ratio but nothing spectacular shows... Only the conclusions above.

For this test I used a HP 8656B and a IFR2945A.

73 de Adrian YO3HJV

5 comentarii:

PE4BAS, Bas spunea...

Thanks for this usefull review Adrian. Have yopur heard of the first firmware update of the IC-7300?
Hope to buy one of these radios at the end of the year. 73, Bas

Adrian (YO3HJV) spunea...

I already updated the radio next day the update was released. And i feel pitty! Icom killed "Quick Memu"!

Robin spunea...

Did you measure the 2nd harmonic of your signal generator?
I did on mine.
so.. 0dbm on 7.150 on my IC-7300 that is a signal of S9 +55 dB!
Then on 14.300 I see a signal of S9 +18dB but it is not clear cut.. as on my Anritsu signal generator, when connected to the spectrum analyzer, the 2nd harmonic is -48dB down on the 7.150 MHz fundamental.. So considering the Rig is being overloaded on 40m, I think it is doing just fine on 14Mhz, and it is NOT being oversensitive to a harmonic from the 40m band at all!

YO3HJV, Adrian spunea...

Well Robin, this is a good point! I will measure it and update the post. Thanks for the suggestion!

YO3HJV, Adrian spunea...

Well Robin, this is a good point! I will measure it and update the post. Thanks for the suggestion!

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