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IC-7000 evaluation

Icom's IC-7000 is a successor to the quite successful IC-706 series, though at substantially higher price than current IC-706IIG prices. The IC-7000 is a small mobile / home station radio, all modes, covering 160m to 70cm bands.

This article looks at characteristics that are important to my applications for the IC-7000. The article is not about measurement of receiver IMD, blocking, dynamic range etc, there are plenty of sites on the net that focus on that perspective of radios.

General

Frequency stability

Fig 1: Warm up frequency drift

The warm up characteristics shown in Fig 2 indicate that the reference oscillator is not temperature controlled.

Fig 2:Frequency drive with ambient change

The temperature sensitivity of the frequency shown in Fig 2 indicates that the reference oscillator is not very well temperature compensated. Experience shows that the frequency error changes with the heat associated with transmission by up to 1.0ppm.

In summary, the frequency stability is not sufficiently good to use with narrowband / frequency critical modes above 30Mhz. (The user manual does not list a higher stability reference oscillator option.)

Notch filters

Automatic notch filter

The automatic notch filter was evaluated on a high m FM signal from a SSG that is 20dB above the noise floor. Fig 3 shows the received spectrum before application of ANF.

Fig 3: "Interfering tones" before application of ANF

Fig 4 shows the reduction in steady tones with application of ANF.

Fig 4: "Interfering tones" after application of ANF

Manual notch filter

The manual notch filter provides one or two filters adjustable in centre frequency and three width options. The facility is effective and easy to use.

AGC

The AGC works well generally, but responds to very short impulses  which silence the receiver until the AGC recovers. The Noise Blanker is effective in limiting such pulse, and provides a method of working around this problem.

S-meter calibration

The SSB S-meter appears calibrated to the convention of 50μV in 50Ω for S9, and 6dB per S-point with the pre-amp ON (differently to the IC-706). Fig 5 shows the results of a rough test of S-meter calibration.

Fig 5: S-meter error

S-meter error is high outside of the range from about S3 to S9+30dB.

Note that the WFM S-meter calibration is different to SSB.

ATU interface

The IC-7000 supports the AH-4 auto tuner. However, the way in which it interacts with the ATU is different to the implementation in the IC-706IIG. If the radio's Tune button is pressed, a tune process is initiated. If the Tune button is pressed whilst a tune is in progress, the radio aborts the tune process, but does not send a reset to the ATU (as does the IC-706IIG, nor does it restore PTT operation until an internal 20s timer expires. This may affect devices that use this interface.

There are a number of devices that use this interface to emulate a tuner, so that a steady low power tune carrier can be obtained from the radio conveniently, or for integration with third party devices such as screwdriver antenna tuners. The cheap and nasty designs will probably not be impacted by the absence of reset, but more intelligent devices that acted on the reset and were immediately available for reuse may be affected. Correspondence suggests that the IC-7000 also uses the KEY control line for part of the temperature sensing / fan control function, and that the simple ("cheap and nasty") resistor / capacitor tuning devices that were often used on IC706IIGs do not work properly with the IC-7000.

 The TuneMate for Icom transceivers which does respond to the reset signal is affected by this change, and has an optional switch for optionally resetting the device and the transceiver prior to the TuneMate's 18s timeout.  I have released a new version of firmware (V1.4) which allows the optional TuneMate switch to initiate a tune as well as to terminate the process as a further convenience.  The TuneMate does NOT disrupt the temperature sensing / fan control function of the IC-7000, TuneMate uses a tri-state output pin which either pulls the key line to ground or is in the "open" which is equivalent to the open collector output from the IC-AH4.

Icom's variable implementation of the ATU interface, and the lack of a clear published protocol is a frustration to owners wanting to interface non-Icom equipment with the radio.

If Icom were smart and responsive, such devices would not be needed, Icom would have added a software feature that in the absence of an ATU, the Tune button fired up a 10W CW carrier for tuning purposes, and ceased the carrier on a subsequent Tune push or timeout.

RIT

The RIT is not as convenient as on the 706IIG, which is a pity since so newly minted hams are not accomplished at tuning in SSB signals, necessitating the use of RIT to avoid "walking" up or down the band with each over.

Dial

The dial is much smoother, with optional detents. A great improvement.

Metering

The IC-7000 has full SWR metering on the VHF and UHF power modules, an improvement over the IC-706IIG.

DC lead

Icom has chosen to use a different DC connector on this radio to the predecessor IC-706IIG and many other Icom, Kenwood and Alinco radios. That is to some extent a blessing because the older 6 pin connector is dangerous in its applilcation on some mains power supplies. Nevertheless it necessitates manufacture of new power cables.

The pins in the new connector seem flimsier than the older 093 series Molex style pins, but time will tell if they are up to the task.

Fig 6 shows the new power connector, in this case connected to pair of red/black 2.5mm2 twin lead, one conductor for each pin, and inserted in 8mm vinyl sleeve for tidiness.

Fig 6: The IC-7000 power connector

Figure 7 shows the pre-insulated crimp spade connectors (FS5.5-6) applied the to pair of red/black 2.5mm2 twin lead. Note the identifying heat-shrink to aid in correct polarity. The heat-shrink sleeves have a single wrap of hot-melt tape on the yellow connector sleeve. If hot-melt tape is not readily available, a little hot-melt glue from a glue gun could be applied and reflowed during the shrinking process.

Fig 7: Spade connectors for power supply attachment

Anderson Power Poles are also used for DC wiring, so another lead terminated in those connectors was manufactured. In this case, two like polarity twin lead conductors are terminated in a single Power Pole terminal.

Realisable sensitivity

Amateur equipment is often designed with receivers that exhibit exceptional sensitivity in a test environment, but that sensitivity is not realised when connected to an antenna. There are two factors that commonly limit the sensitivity that can be realised when connected to an antenna:

Amateurs often refer to this effect as "pager interference".

The following explores the "usable" sensitivity of the IC-7000 in an on-air scenario.

The test environment is:

The general test configuration is shown in Fig 8. Not all components are in line for each test, see Table 1 for details.

Fig 8: On-air sensitivity test configuration.

Table 1 summarises the tests in a range of configurations. The System Sensitivity is the key metric, and is with reference to the output connector of the directional coupler.

Table 1: Summary of on-air sensitivity measurements on 144MHz.
Item Antenna Signal
Generator
(dBm)
Filter Attenuator

Receiver

System
Sensitivity
(dBm for
 10dB
SINAD)
Shortfall
(dB)
Comment
Attenuator Preamp
1 50Ω term -76 NO NO OFF ON -126   Receiver sensitivity measurement - baseline
2 50Ω term -70 NO NO OFF OFF -120   Receiver sensitivity measurement
3 50Ω term -69 YES NO OFF ON -119   Filter loss measurement (7dB in situ)
4 D-130 -46 NO NO OFF ON -96 30 Preamp ON
5 X-50 -48 NO NO OFF ON -98 28 Preamp ON
6 D-130 -60 NO 10dB OFF ON -110 16 External 10dB attenuator, Preamp ON
7 X-50 -64 NO 10dB OFF ON -114 12 External 10dB attenuator, Preamp ON
8 D-130 -55 NO NO ON OFF -105 21 Internal  attenuator, Preamp OFF
9 X-50 -56 NO NO ON OFF -106 20 Internal  attenuator, Preamp OFF
10 X-50 -56 NO NO OFF OFF -106 20 Preamp OFF
11 D-130 -66 YES NO OFF ON -116 10 Filter, Preamp ON
12 X-50 -68 YES NO OFF ON -118 8 Filter, Preamp ON

Comparing the sensitivity achieved in a laboratory sensitivity test at row 1 (which exactly meets the specifications), with the System Sensitivity realised with the D-130 and X-50 antennas connected, the realisable sensitivity is 28 to 30dB worse than specification. Certainly the external ambient noise contributes to that, but the results of tests 6 to 12 indicate that the lion share of that loss of sensitivity is intermodulation products generated within the receiver:

Table 2 compares the system Sensitivity of the IC-7000 bare (no external filters or attenuators) with the TS2000 bare. The TS2000 is an older Kenwood transceiver which sells second hand in the market for a little less than the price of a new IC-7000 at the time of writing. Note that although the TS2000 has poorer sensitivity in a laboratory test, it is far superior (20dB better in this test) on the air due to less IMD noise.

Table 2: Comparison of System Sensitivity of IC-7000 and TS2000 at 144MHz.
Antenna

System
Sensitivity
(dBm for
 10dB
SINAD)

 

IC-7000 TS2000
50Ω load -126 -122
X-50 -98 -120
D-130 -96 -116

These results depend on the environment at the time and place of the tests, and rerunning the tests in a different place or time may produce different results. The locality where the tests were run is residential, a small non-industrial city of about 300,000 population, which by experience with the commercial centres of Sydney and Melbourne is relatively quiet.

Anecdotal evidence is that Icom fixed the severe IMD problem apparent in the VHF/UHF bands on the IC-706IIG. These test results suggest that if they improved it, they haven't improved it to the point that it would be considered a good receiver... the problem isn't fixed!

FSM

Introduction

FSM (for Field Strength Meter) is a software application that extends a conventional SSB receiver to allow measurement and calculation of field strength of radio signals or interference. more...

This section deals with receiver characteristics that are important to use with FSM.

Effective Noise Bandwidth

The bandwidth of a receiver determines the total power that reaches the detector from a wideband source of noise or interference. The response of receivers is not ideal, and knowledge of the Effective Noise Bandwidth is important to measurement of wideband noise and interference.

IF pass-band response was measured in the default 2400/sharp filter setting. The pass-band response is shown in Fig 9. Applying a 120Hz low-cut filter, and analysing the response, the Effective Noise Bandwidth wrt gain at 1kHz is 2090Hz. The -6dB points are at 220Hz and 2750Hz, giving a nominal bandwidth of 2530Hz at the -6dB points.

Fig 9:IF pass-band response 2400Hz/Sharp

Linearity below AGC onset

FSM depends on the linearity of the receiver below AGC onset, and the range of this linear region is important for FSM measurements. IC-7000 AGC gain compression occurs at 30dB above the receiver noise floor, which is higher than for most comparable receivers. Fig 10 shows the linearity for FSM purposes.

Fig 10: FSM linearity

Standard Deviation of the Error is 0.12dB (64k samples in FSM).

Example FSM measurement

Fig 11 shows the FSM screen at the completion of measurement of ambient noise on 7MHz using the IC-7000. The measurement was made with an external 12dB fixed attenuator which provided plenty of attenuation to prevent AGC operation and allow valid measurement. In this case, the RMS normalised FS is -39.1dBμV/m, about 3dB below ITU-R P.372-8 expected Rural noise.

Fig 11: FSM measurement of ambient noise on 7MHz with IC7000 and 12dB external attenuator

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