IC9700 ICOM : Résistance aux signaux forts

I have only measured the IC-9700 on 2 meters as of now.  The dynamic range at any test spacing is 74 dB for my sample.  It is believed that the ADC in the 9700 does NOT have a “dither” feature in the ADC chip.  Assuming this is correct, I have no idea what IP+ is supposed to do.  In any case the IFSS curve that shows third-order distortion from –57 dBm to -30 dBm shows almost no difference with or without IP+.

Understanding that my long form at present only covers 2 meters, a PDF of it is available on request to either rob@sherweng.com or rob@nc0b.com

73, Rob, NC0B

Last night during the 432MHz UKAC contest I heard what appears to be images of a strong local station, I noticed them because one happened to land on the frequency I was trying to work on.
He was calling on 432.238MHz , and I could hear the images on approx +/- 75KHz. The Overload indicator was not indicating. The strong station was approx S9+40. experimenting with PREAMP/ATTEN/ IP+ appeared to have little effect. Reducing the signal strength of the main signal by altering the beam direction reduced the levels of the spurious signals apparently proportionately with the reduction in the main signal

Experimenting today I can reproduce the effect using a signal generator. Using a Marconi 2041 I find that the 'images' can be easily heard for received signal strengths of the main signal above an indicated S9. The spacing of the 'image' response varies with the operating frequency.for a Signal frequency of 432.100MHz the responses appear to be approx +/- 37KHz.

Has anyone else encountered this problem?

Stephen Tompsett (G8LYB)

I must admit that I kept hearing "images" of a particularly strong local station (he was over 59+60 with both pre-amps off !!!) but I assumed it was due to the fact that he was SO strong.

It did feel that the strong signal handling wasn't as good as the SunSDR2-Pro + Iceni combination that I usually use but I would need to have them both setup to do a proper comparison I suppose?

Phil (M0VSE/P)

Phil and others…. I wondered how long it would be before someone reported receiver overload in the 9700 radio. I likewise own a SunPro2 Pro SDR radio, which includes the two meter band. In the US, we have APRS operating at 144.39 FM. I have an APRS station close to me that is +40 or more over S-9 and the SDR receiver in that radio also overloads when the APRS station is operating and that is nearly all the time. The result is that his signal is very loud for about 100 kHz. And the signal can be seen on the monitor down to the low edge of 2 Meters. This is going to be a problem in the USA for sure.

This issue does not occur using my old but great TS 790S nor while using a 2 meter DEMI transverter with TS 590SG IF. It is noticeable if I plug the transverter into a K-3 radio if the digital NF is engaged.

My question is whether SDR radios in general are truly capable for weak signal communications on todays VHF/UHF bands.  Can not wait to see more test results on this important issue.  

Dick  W5AK

I haven’t even started looking at 70cm yet, however I did look at spurious responses last night on 2 meters. I fed in an S9 +60 dB signal which is -25 dBm on 144.200 MHz. To be sure I wasn’t seeing a spur in my signal generators I used both a HP 8662A and a 8642A. They have completely different architectures, so a spur would not be on the same frequency.


I found 6 spurs, three very weak and three just below the S meter threshold which is 1 microvolt, or -107 dBm.  The measurements were with the preamp OFF.  The OVF level with no preamp is -8 dBm, which is very similar to the 7300 and 7610 of about -10 dbm.

Rob, NC0B

The problem I experience with my unit is experienced a long way before the set complains of an overload I've been using an input level of -40dbm which is  a bit above an indicated S9+40db, well on the S meter scale...

It isn't a simple inter-mod problem because the problem can be demonstrated with a single carrier.

The problem doesn't appear to be as noticeable (or it's harder to find the spurious signal?) if using a carrier that is a round number of 100Khz, so I am using frequencies like 432.238, 144.238 and 1296.238MHz.

I notice a similar problem on 2m at a comparable input signal level, but I can't find any similar problem on 23cm.
I note that the input level that is causing problems is more than 100db above the minimum detectable signal level.

Has anyone else duplicated or attempted to duplicate this?
Equipment:

• linear power supply.
  
• Marconi 2041 Signal generator, operating in low noise mode 1.
  

Stephen Tompsett

ON4IV a écrit:I have checked and compared the sensitivity of the 9700 and R8600 on the 23cm band. No surprise, the 9700 dominates the R8600, as announced in ICOM's specifications: –126 dBm for the 9700 and –117 dBm for the R8600, a difference of 9 dBm.


The good surprise is the fabulous sensitivity of the 9700, the figure of –144 dBm MDS (with the preamp) obtained by Adam VA7OJ. Relying on my ears and capacity to decode CW, I was able to go down to –150 dBm.


The relatively bad surprise concerns the R8600 whose sensitivity is 13 dBm above 9700's sensitivity (–131 dBm MDS) and –137 dBm relying on my ears, in the same conditions.


Pierre

VA7OJ/AB4OJ a écrit:The IC-9700 has low-noise GaAS MMIC preamps (NJG1152KA1) on 144 and 430 MHz, and a TQP3M9037 ultra-low-noise, high-linearity LNA on 1.2 GHz. It is also band-limited (amateur bands only); this allows a lower front-end noise figure without excessive risk of IMD from strong out-of-band signals.

Being a general-purpose receiver,t the IC-R8600 has a totally different mission. The designers needed to strike a compromise between sensitivity and undesired-signal rejection.
--
73, Adam