Anan7000/HPSDR and Icom IC-7300 S-Meter Calibration

I’ve noticed that my SDR setup, an Apache Labs Anan-7000DLE transceiver used with the PowerSDR software, seems to rest the S-Meter at a quite high level when there is no signal present. This is unnerving when I try to compare my local noise floor with others who claim noise levels many S units below mine. I recently reinstalled PowerSDR and recalibrated the receiver amplitude. While I was at it I thought I’d document the HPSDR power meter performance, and also that of an Icom IC-7300.

These are some screen shots showing before and after calibration, and at the end a comparison with an Icom 7300 radio hooked to the same antenna. All the PowerSDR readings werre taken with the same receiver settings. The mode was set to AM and the filter bandwidth manually set to 2.4 kHz to be consistent with most radios in upper sideband mode. (In PowerSDR the S-meter reading is based on the total power within the bandwidth, so a narrower bandwidth will show a lower noise floor than a wider one.)

First, the display before calibration, first with a 50 ohm dummy load and then with a -50 dBm signal applied:

anan7000-dummy_load-pre_cal

anan7000-minus_50dBm-pre_cal

You can see that the meter reads about 6 dBm lower than it should. I can correct that by using the PowerSDR calibration routine that uses an external signal generator to calibrate the receiver chain. These are the results after doing that:

anan7000-dummy_load-post_cal

anan7000-minus_50dBm-post_cal

Now, the S-Meter shows exactly the signal generator level to be exactly -50 dBm, and the noise floor has gone up by 6 dB as well. The analog meter shows between S2 and S3 which, for -112 dBm noise power, matches pretty well the “Collins Standard” as shown by K9LA’s S-meter calibration table.

Now, let’s connect an antenna and see what happens:

anan7000-doublet_tuned-post_cal

Now the meter shows -89 dBm and S6 to S7, and again that tracks the Collins standard. The other rigs in Carl’s table would show a bit under S5 to S6. The noise floor shown on the spectrum display has gone from about -130 dBm to about -115 dBm.

Now, here’s the Icom IC-7300:

ic7300_s-meter

It’s showing between S2 and S3. For fun, I did a calibration of the IC-7300 S-Meter and came up with this table:

Meter dBm Meter dBm
1st Seg -98.0 S7 –79.0
S1 -96.0 S8 -75.8
S2 -93.8 S9 -72.7
S3 -91.2 S9+20 -54.0
S4 -88.2 S9+40 -34.6
S5 -85.3 S9+60 -16.6
S6 -82.1

It’s pretty clear that the only thing Icom knows about the Collins Standard is that S9 is -73dBm. Below that point the scale is more like 3 dB per unit than 6 dB, and anything below -98 dBm doesn’t exist. That explains the very low noise levels this radio tends to report.

Leave a Reply

Your email address will not be published. Required fields are marked *

You may use these HTML tags and attributes: <a href="" title=""> <abbr title=""> <acronym title=""> <b> <blockquote cite=""> <cite> <code> <del datetime=""> <em> <i> <q cite=""> <strike> <strong>

This site uses Akismet to reduce spam. Learn how your comment data is processed.

RELATED POST

IC-7300 Power Overshoot?

Many people use HF transceivers in situations where they back the power down significantly from full output. Examples are driving…

Add streaming audio to OP25 RPi scanner

Thanks to Graham Norbury, here is how to set up a Raspberry Pi OP25 scanner to stream audio to an…

Thoughts on a Wideband SDR Recording Tool

As part of the HamSci Solar Eclipse experiment, I recorded wideband data from my SDRs on the theory that capturing…

Update on Update on P25 Scanner

Since my updated post on building a P25 trunking scanner with a Raspberry Pi and an RTL-SDR dongle, I've created…