We investigated the innovative qualities for clear transmit signals, receive audio, high RMDR (Reciprocal Mixing Dynamic Range), and the OVF indication, to fully understand their true performance. The FB News staff has turned the spotlight on the OVF (Overflow) function this time.

The 1st article was Transmit Signals: A clean sky by having clean signals.
The 2nd article was Receiver audio: Talking about receive audio.
The 3rd article was RMDR: Increasing the chance of a QSO with rare entity stations.
The Special article was “Is the IC-7610 spectrum scope the best?”
The 4th article is aspecial topic: A thorough inspection of Overflow (OVF).

The 4th article is aspecial topic: A thorough inspection of Overflow (OVF).

IC-7610’s receive performance, spectrum scope capability, transmit signal quality and phase noise characteristics, have been evaluated as outstanding. Now that the "OVF" indication has been added to IC-7610 and IC-7300, the feature may attract people's attention. The FB News staff has turned the spotlight on the OVF (Overflow) function this time.

OVF evaluation

We evaluated the following two points this time.
(1) How does the IC-7610 react when “OVF” appears. (Only the 7610 was evaluated.)
(2) How do the IC-7610 characteristics against extremely strong input signals compare with other SDR transceivers.

The transceiver used as the DUT (Device under test.) is manufactured by company F and it is sold in Japan for approximately six thousand US dollars. We compared both transceivers this time.

■ Test Connections

・Apply a target signal and an interference signal, combined in a power combiner, to both the IC-7610 and the DUT through an antenna splitter.
・Begin sending CW signals from the transmitter. Set the level of the target signal low enough that the IC-7610 and the DUT transceiver’s S-meters do not show any indication, but enough that you can faintly hear the target CW signal from the speakers.

● Analysis 1
Set the IC-7610 preamplifier to OFF and the DUT preamplifier to +20 dB. These settings make both transceivers’ receiver sensitivity －133 dBm. Keep the target signal level constant and gradually increase the interference signal level. Then confirm how high an interference signal level can be applied to each transceiver until just before overflow occurs, and whether or not the transceiver can still receive the target signal at that level.

Receiver MDS* sensitivity for the transceivers are:
・IC-7610: －133 dBm
・DUT: －119 dBm
Note: A more negative number indicates a smaller signal level. *(Minimum Detectable Signal)

Test conditions
・Receive sensitivity: Approximately －133 dBm
・Operating mode: CW   BW: 500 Hz
・Frequency separation between the target signal and the interference signal: 10 kHz

The received audio of both transceivers are recorded. Try to listen to the audio with stereo headphones. (Left: IC-7610 audio, Right: DUT audio.)
Note: Listening to audio with a headset at high volume levels may cause a ringing in your ears, so reduce the volume level or simple listen through the speakers.

Result
Both transceivers can receive the target signals without any differences with an interference signal level of －20 dBm. However, the DUT transceiver does not receive the target signals in the overflow condition with an interference signal level of －19 dBm. The IC-7610 OVF indication lights, but the transceiver can clearly receive the target signal when the interference signal level is even increased another －10dBm. Again, the IC-7610 can receive the target signal when the signal level of the interference signal is increased to 0 dBm. Surprisingly, the IC-7610 can still receive the signal without the audio breaking up, or any distortion, even when a +5 dBm signal is applied.

・Signal strength verses receive conditions

Yes: Receives the target signals clearly.　
Yes: ”OVF” appears, but still receives the target signal.
No: Does not receive the target signal in the overflow condition.

● Analysis 2
Next, turn the preamplifier OFF on the DUT transceiver and set the IC-7610 attenuator for +12 dB. These settings make both transceivers the same sensitivity for approximately －119 dBm. We increased the interference signal level gradually and verified to know how both transceiver receive the signal.

Test Conditions
・Receive sensitivity: Approximately －119 dBm (IC-7610: Attenuator ON: +12 dB, DUT transceiver: Preamplifier: OFF)
・Operating mode: CW, BW: 500 Hz
・Frequency separation between the target frequency and the interference frequency: 10 kHz

Reception sounds for both transceivers are recorded. Try to listen to the audio with stereo headphones. (Left: IC-7610 audio, Right: DUT audio.)

・Signal strength versis receive conditions

Yes: Receives the target signals clearly.
Yes: ”OVF” appears but still receives the target signal.
No: Does not receive the target signal in the overflow condition.

Result
When applying an interference signal of +1 dBm, the IC-7610 OVF indicator appears but both the IC-7610 and the DUT transceiver clearly receive the target signal. The interference signal is increased to +2dBm, and the DUT transceiver stops receiving. However, the IC-7610 can receive the signal without any problem. It can even receive the target signal when the interference signal is increased to +10 dBm. That is a big difference.

● Analysis 3
Test Conditions
・Operating mode: CW, bandwidth: 50 Hz
・Separation between the target frequency and the interference frequency: 200 Hz
・Interference signal level: －10 dBm
・Attenuator: OFF
・AGC: OFF

We set the filter bandwidth at 50 Hz (narrowest) and made the frequency separation 200 Hz, the severest parameters. Then, we verified whether overflow occurred in the IC-7610.

Result
The IC-7610 can receive the target signal without distortion of the received audio, even when the OVF indication lights. The transceiver has almost no occurrence of blocking caused by the interference signal.

Summary
Actually, receive overflow means “completely no receive.” We have discovered through this experiment that the OVF indicator appearance in the IC-7610 does not mean “No receive.” Furthermore, the IC-7610 steadily received the target signal, even after the OVF indicator appeared when the interference signal level was drastically increased. To compare with the higher class of the SDR transceiver (such as the DUT), the IC-7610 does not have the “No receive” overflow condition.

We think that you can understand that when the IC-7610’s, or the IC-7300’s, OVF appears, it indicates that a strong signal exists in the band that is being received. When the OVF indicator appears, and you feel something is wrong with the received audio, it may be better to turn OFF the preamplifier, decrease the RF gain with the RF GAIN control, and, if necessary, turn ON the attenuator, and set it at an appropriate level.