JI1FGX/DU9 Measuring the receiving sensitivity of the IC-820H using the HP 8656B signal generator (2026/08/05)

JI1FGX/DU9 Amateur Radio Diary, Mindanao, Philippines, IOTA OC-130

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Contents by Year:

26/08/05	IC-820H Receiver Sensitivity Test
26/08/02	Satellite SatBox Development in Progress - Part 2
26/07/16	Delivery of the 3D printed panels
26/07/09	Development of SatBox for satellites
26/07/05	Weather Monitor Indoor Unit
26/06/30	Creating data for 3D printers using FreeCAD
26/06/16	Installing an AS5600 magnetic encoder on a KR-500.
26/06/05	Grandson Zion's CQ
26/06/04	Replacing the potentiometer on the KR-500 elevation rotator
26/06/03	Making a Repeater Controller Pert4
26/06/01	Weather Monitor software
26/05/31	Weather Monitor
26/05/21	JTDX Auto Run BUGFIX
26/05/17	Repair of satellite antenna system
26/05/13	Repair of Alinco DR130
26/05/07	Making a Repeater Controller Pert3
26/05/03	Indonesian satellite friend YC8RPK
26/04/26	DXCC200 achieved
26/04/23	Communication via ISS voice repeater
26/04/20	WSJT-X Auto Run Ver0.1.5
26/04/19	Got an Alinco DR-130
26/04/15	Clublog Charts
26/04/10	Regarding POC transceivers
26/04/08	Using KENWOOD AT-300 with YAESU radio
26/03/17	How to establish a radio club in the Philippines
26/03/10	KENWOOD AT-300 with YAESU radio
26/02/27	Philippine NTC Amateur Radio License Examination Question Bank
26/02/20	Package received from JK1SNS
26/02/18	Temporary License Renewal
26/02/14	Satellite Tracking Software SatTrack
26/02/05	Making a Repeater Controller Pert2
26/02/02	CQ on satellite IO-86
26/01/27	Shack & Repeater Controller
26/01/16	Making a Repeater Controller
26/01/16	Making aRotator Interface PCB
26/01/10	Satellite antenna installation
26/01/08	WSJT-X Remote Operation
26/01/07	JTDX Remote Operation
26/01/04	log_reciver_Ver2.6.6
26/01/04	Tailscale VPN software for JTDX_Remote

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Measuring the receiving sensitivity of the IC-820H using the HP 8656B signal generator (2026/08/05)

The transceiver used for satellite communications is the ICOM IC-820H.
It was introduced in 1994 and is now over 32 years old.

Recently, someone suggested that the IC-820H might have a receiver sensitivity problem.
Although my uplink signal was being received very strongly by stations in Japan,
there were occasions when I was unable to hear them calling me and therefore could not respond.
In addition, I could sometimes hear that several Japanese stations were working each other through the same satellite,
but I was unable to receive some of their signals.
This led me to suspect that the sensitivity of the UHF receiver might have deteriorated.

However, under good conditions my own UHF downlink signal is received very strongly,
so I was not convinced that the receiver sensitivity had actually degraded.
To verify this, I decided to measure the receiver sensitivity of the IC-820H using an HP 8656B RF Signal Generator.

To investigate the problem, I pulled out my HP 8656B RF Signal Generator, which I had bought second-hand 17 years ago.
The HP 8656B is a synthesizer-based RF signal generator introduced around 1986, making it about 40 years old today.

My first impression was, "Wow... it's huge and heavy!" It weighs approximately 15 kg.

Since it had not been powered on for 17 years, I was a little concerned.

Would it even power up?

Had the electrolytic capacitors deteriorated?

Would it produce any unusual noises or strange smells?

With these concerns in mind, I switched on the power.

As expected from HP, the instrument powered up perfectly.
The LED display lit normally, and there were no unusual noises, strange smells, or signs of overheating. It started up flawlessly, despite being a 40-year-old piece of test equipment.

First, we measured the reception sensitivity using VHF.

Measured at 145.900MHz using an IC-820H FM radio.
-120 dBm	No S-meter deflection only faint noise
-110 dBm	S2
-100dBm	S7
-90 dBm	S+10
-80 dBm	S+40
-70 dBm	S+60

Next, we will measure the reception sensitivity of UHF.

435.640 MHz IC-820H Receiver Sensitivity Test.
Signal Generator Output.	FM Mode.	SSB Mode.
-120 dBm	No S-meter deflection only faint noise	No S-meter deflection only faint noise
-110 dBm	S3	S4
-100 dBm	S8	S8
-90 dBm	S+30	S+20
-80 dBm	S+50	S+30
-70 dBm	S+60 (full scale)	S+40
-60 dBm	-	S+50
-50dBm	-	S+60 (full scale)

The measurements showed no significant problems with the VHF or UHF receiver sensitivity of the IC-820H.

The coaxial feed line consists of 20 meters of LMR-400 and 4 meters of LMR-240, with a total loss of approximately 2 dB at 435 MHz.
The measured SWR during transmission was 1.2, indicating that both the feed line and antenna system are in good condition.

One possible improvement would be to install a mast-mounted receive preamplifier.
The ideal choice would be the genuine ICOM AG-35, but it has long been discontinued and is now difficult to obtain.
When one does appear on the used market or at auction, it usually sells for a high price.

Even without a preamplifier, I have successfully completed many QSOs through RS-44,
demonstrating that the current system already provides good practical performance.
If I am able to obtain an AG-35 or a similar low-noise preamplifier in the future,
I would like to evaluate how much it improves the reception of weak satellite signals.

August 2, 2026. August 5, 2026.