Adjusting the S-Meter in HDSDR

Since ICOM has released Firmware v.1.42 for the IC-7610 the I&Q port is working again. This opened up the possibility to use HDSDR (Sampling rate of 1.92MHz with an effective Bandwidth of 1.66MHz) again. Since I still had the S-Meter check setup "set up" from the "Adjusting the S-Meter in Thetis"  I decided to check and adjust, if need be, the HDSDR/IC-7610 combo.

The setup is basically the same as for Thetis, except the SDR in this case is an IC-7610.

Setup:

• Signal generator: XG3
• Level: -34.8dBm @ 13.8V
• Att: HP-355C & HP-355D (38dB for approx. -73dBm level)

In HDSDR under Options [F7] we find Calibration Setting. This opens the HDSDR Calibration Panel.

Selecting the S-Meter Calibration tab:

The current configuration seems to correspond to an S-Meter reading of S9 +10dB on HDSDR:

and an S9 on the ICOM without the Pre-Amp engaged.

So next we add -73dBm to the Correct Level [dBm] field and press the [Calculate] button.

And the result is:

reducing attenuation by 6dB we get:

and, as expected, adding 6dB we see:

So in a Software Defined Radio (SDR) application written by Amateur's we do get the proverbial 6dB per S-Unit. 

Adjusting the S-Meter in Thetis

After about five (5) years I resurrected my ANAN 100D again. Trying a few versions, including a development version, I settled on Thetis v2.10.3.5 x64 u2. Seems to be running fine on my Windows 11 system. Quite a few improvements over the last five years. Going through the Setup/Configuration of the system I stumbled over a Level Cal inside the [Calibration] tab which can be found under the [General] tab. This allows one the ability to "automagically" set the S-Meter to a user provided level, .... sweet ....

I've decided to use my trusty old Elecraft XG3 RF Signal Source which I have checked against a calibrated RF Powermeter. At 20m the output at the -33dBm level measured -34.8dBm @ 13.8V. So using an attenuator with 38dB attenuation  will give me a -72.8dBm level into the ANAN. A short RG58 cable into a MFJ-1700B switch and another 50cm of RG58 should compensate for the missing 0.2dB to make it -73dBm.

Setup:

• Signal generator: XG3
• Level: -34.8dBm @ 13.8V
• Att: HP-355C & HP-355D (38dB)

And this is how it look in real live.

Here is the Thetis setup:

After pressing the Level Cal [Start] button, the system goes and runs an internal calibration routine. A window pops up to inform us about the progress status of the calibration.

Well, the result is quite pleasing. 

And if we add 6dB attenuation we get:

And not to forget if we do subtract 6dB attenuation the result is:

Struth, 6dB steps who would have thought that is a possibility. 

Oh and this is at every SSB Bandwidth we choose. My default is 2K1, however if I choose 2K9 the S-Meter still shows -73dBm. Yikes, it is possible! It is software defined after all.

It would be nice if my IC-7610 would not change the S-Meter reading with the engagement of the Pre-Amp(s).

References:

• A Little History about S-Points
• IARU Standards
• The beginning of the S-Meter revolution
• IARU Technical Recommendation R.1

IM improvements using DPD with a SSPA

The question that a lot of users seem to have on their mind is "What benefits, if any do I get by using ICOMS DPD in conjunction with a Solid State Power Amplifier (SSPA)"

Well, I measured a 6dB improvement. 

Measurement setup:

• SPECAN: SDR-IQ
• TAP: VK5HW (50dB)
• ATT: 20dB
• PWR: 1000W
• ANT: Dummy Load (VSWR 1.08:1)
• Software: SpectraVue V.3.44 Beta 0

DPD off

Two tone test:

Result:

1st Value    -31.311dB

2nd Value    -31.455dB

3rd Value    -52.398dB

4th Value    -53.545dB

IM Max     -22.2dB

IM Avg     -21.6dB

NOTE: 1st and 2nd are the two tones and 3rd and 4th are IM3.

Look at IM3 and IM5, they are nearly the same in strength.

And the below using my Voice Caller calling CQ:

Result:

1st Value    -23.996dB

2nd Value    -31.168dB

3rd Value    -49.526dB

4th Value    -53.689dB

IM Max    -29.7dB

IM Avg    -24.0dB

DPD ON

Two tone test:

Result:

1st Value    -31.168dB

2nd Value    -31.311dB

3rd Value    -58.996dB

4th Value    -59.139dB

IM Max    -28.0dB

IM Avg    -27.8dB

Well, we do see about a 6dB improvement on the two tone test which is better than a Mosquito fart. But I believe the below is quite a good example on how well it improves your VOICE signal!

And below, using my Voice Caller calling CQ:

Result:

1st Value    -20.840dB

2nd Value    -27.582dB

3rd Value    -57.750dB

4th Value    -60.143dB

IM Max    -39.3dB

IM Avg    -34.7dB

On average we see an improvement of 7dB again better then a Mossi fart.

So I'd say any improvement, be it only 6dB is an improvement. As such I would recommend to upgrade the IC-7610 firmware and enable DPD however, YMMV ....

ICOM IC-7610 Firmware Ver. 1.42 DPD IM measurements

A quick update on my IM measurements for the ICOM IC-7610 with the new Version (V1.42). This Version is the third installment for the '7610 and this one has the I&Q output fixed. I've not tested this but I believe that quite a few forum members have done so and are over the moon.

Here are a few IM measurements I made after the Firmware upgrade.

TRX: ICOM IC-7610

SPECAN: SDR-IQ

SOFTWARE: SpectraVue 3.44 Beta 0

TRX Power: 35W

The above shows the output without DPD. About 23dB 

NOTE: This is 6db below PEP. 

Here we see the same two tone signal with DPD enabled, a nice 54dB down on IM3 and all other IM products are below -140dB. Again, this is 6dB below PEP. So pretty darn good if you'll ask me.

And so the question remains, is it worth to enabled DPD even if we would use an amplifier? I'd say definitely. Using an Amplifier with a much cleaner exciter would give you a cleaner signal (yes yes it depends on a few other things but hope prevails ....)!

Remember GIGO (Garbage in = Garbage out)! This is also true for RF amplifiers not only for Computer Systems.

Nice going ICOM.

See the below pictures how my signal looks over the air. Solid state Amp and DPD enabled. 

• 20m
• 40m

Current TX Setup

Currently I do not use the dbx in the audio chain. I use an old HEIL PROSET PLUS (HPP) headset which I purchased second hand. Now the headset itself is just average, normally I'd be using a Sennheiser for its nice fit, excellent sound reproduction and lightweight. However, the HPP headset does have the original HC4 and HC5 microphone inserts and because the dbx in in service for a different radio I opted for the HPP for the time being.

The current setup is:

• HHP (HC5)
• TX Bass: +3
• TX Treble: +4
• TBW: 200-2500
• COMP: 8
• MIC GAIN: 35%

Is my NOISE FLOOR (NF) really worse than yours ?

Well, let's answer that question first so you can move on to better things in life. And the answer is:

No it is not, because I use an S-Value indicator (S-Meter) that follows a Standard! The so called 6dB per S-Point (6dB/S) standard!

And that's it, 73 and catch you on the bands (as they say).

Oh, hello you are still here. So, it looks like you would like to know a bit more about this phenomena. Well, then read the below or maybe this "What is your S-Meter Really Displaying".

As far as I know, most Amateur Radios Transceivers from the three main manufactures, ICOM; YAESU and KENWOOD seem to display a 3dB/S scale below S9 (-73dBm). 

So if I read a Noise Floor (NF) of S3 on my S-Meter, which by using the 6dB/S standard would be -109dBm or -2.0dBμV NF.  And my QSO partner, i.e. you, is stating a NF of S2 which, using the applied 3dB/S scale would be a NF of -94dBm or -13dBμV.  

So is my NOISE FLOOR really worse than yours?

Let's have a look at the below two Tables, the left one is scaled in 6dB per S-Value i.e. my S-Meter and the right in 3dB per S-Value like your S-Meter. 

Received Power (Zin = 50 Ω)	Signal Strength S-Value 6dB step		Received Power (Zin = 50 Ω)	Signal Strength S-Value 3dB step
-121 dBm	1		-97 dBm	1
-115 dBm	2		-94 dBm	2
-109 dBm	3		-91 dBm	3
-103 dBm	4		-88 dBm	4
-97 dBm	5		-85 dBm	5
-91 dBm	6		-82 dBm	6
-85 dBm	7		-79 dBm	7
-79 dBm	8		-76 dBm	8
-73 dBm	9		-73 dBm	9

Doesn't that shed some light on this (issue)?

According to the IARU Handbook (Ver 9.0) Paragraph 4.1.3 S-Meter Standards:

1. One S-point corresponds to a level difference of 6dB.

2. On the bands below 30 MHz a meter deviation of S-9 correspond to an available power of a CW signal generator connected to the receiver input terminals, of -73dBm.

3. On the bands above 30 MHz a meter deviation of S-9 correspond to an available power of a CW signal generator connected to the receiver input terminals, of -93dBm.   

It has been a Standard for quite a while, but it seems that it has not been adapted widely.

Signal Level Strength Meter Calibration and IARU Standards

ICOM IC-7610 Digital Predistortion

Well it was only a matter of time (a long time though) that one of the big three Amateur Radio Suppliers would follow the ANAN "PureSignal" crase. 

So what is this Digital Pre-Distortion or DPD for short anyway.

Well, a tiny winey bit of techo talk first.

Every radio has an RF amplifier. This is a component which does add to the performance, and as such to the communication distance of the radio. Sometimes we use an external amplifiers to increase the performance of our radio and even though we call our amplifiers "Linear-amplifier", the RF amplifiers is quite a non-linear device. This nonlinearity creates spectral growth (IM) which leads to interference of adjacent channels. 

Please note that the above is a very, and I really mean a very simplified view.

DPD is a technique to linearise an amplifier, which is basically a mechanism to improve the cleanliness of one's transmission, i.e. to reduce the spectral growth, also known as intermodulation (IM) products.

If you like to get a better understanding of DPD, checkout this description, an excellent read.

To enable DPD on the IC-7610 we need to update the Firmware of the radio to the latest firmware version, Ver. 1.40 available from ICOM Japan.

And before we go any further I'll answer the most important question first!

 "So is it working?"

Yes!

To show you the difference between DPD and non-DPD I've created a few screenshots using 100W into a RF Dummy Load and using my SDR-IQ as a Spectrum Analyser. The transmitted output power of the radio has been set to 100W for these tests.

Pictures 1 and 2 are using a two tone signal recorded and installed onto the IC-7610 TX Voice memories.

Picture 1: 2-tone audio signal, DPD OFF

Picture 2: 2-tone audio signal, DPD ON

And Pictures 3 and 4 are plain old voice signals.

Picture 3: Voice signal, DPD OFF

Picture 4: Voice signal, DPD ON

As can be seen the "crud" (IM) has been reduced quite a bit. I'd say about 20dB more cleanliness. Quite an improvement. 

So onto how to set this up. But first a note:

Before we can enable DPD we need to add a RF Dummy Load to one of the Antenna Ports of the Radio. 

This Dummy Load needs to have a reasonable low VSWR of at least 1.5:1 across all the bands that we would like to use with DPD.

So if we go into the SET Menu we should see a new Menu entry. The DPD Adjustment Menu as depicted in Picture 5. (Only after the installation of the Firmware Ver. 1.40)

Picture 5

If we select the DPD Adjustment Menu we have the option of selecting three different adjustments. Since I don't have an ICOM PW-2 I did select the IC-7610 Single Adjustment.

Picture 6

If you are the owner of an ICOM PW-2 you would follow the setup/adjustments as per the PW-2 manual. 

NOTE: At this stage I have not found a way to integrate my Amplifier into the DPD loop. It is fairly simple using only a TAP to feed an AC (RF) voltage back to an ANAN radio for DPD (Pure Signal) however, this doesn't seem to be the case with the ICOM. It looks like a little bit more trickery is involved to make the feedback loop work with a non-ICOM amplifier.

However, it is still a worthwhile improvement to utilise DPD only on the Radio. 

Remember: 

Garbage into the Amplifier means a lot of Garbage out of the Amplifier.

So by cleaning up the signal to feed your amplifier you will gain lots of brownie points within the community.

The next step is to run the adjustments per band you'd like to operate and use DPD on.

Picture 7

As you can glean from Picture 7, I have run the DPD adjustments successful on most of the band I will operate on. This is indicated by a tick and pawn icon next to the Band designator. 

And you're done.

Try it and be one of the "cleaner" signals on our bands. 

Additionally, if you don't have DPD the following most likely will help you to become one of the cleaner signals on the band. To reduce this nonlinearity, we could operate our amplifier at a lower power so that the active device in your (Linear)-amplifier (the power transistor or valve) will operate within its linear region.

Who would have thought that that is an option. 

Oh, and if you do not believe me maybe the below quote from the ARRL-LAB will convince you.

Excerpt: (Page 38 - Lab Notes: RF-KIT RF2K-S)

shows that a slight reduction in power makes a significant difference in the cleanliness of the transmitted signal, improving the third-order IMD performance to –45 dB PEP.

Update: 

The below is my signal on 20m:

And on 40m:

Controling the RF-KIT Amplifier via UDP

Having gone through the trials and tribulation of online "shopping for answers" I thought I better write down how I got my amplifier to follow the band/frequency of my radio, an ICOM IC-7610.  

Please note: Many ways lead to Rome, as well to a solution for the amplifier to follow the Radios frequency/band. This is only one of the many.

Since I've already control my radio from my PC via the logging program from DXLAB, it was quite easy to Setup the amplifier to follow the radios frequency/band after some very good information had been passed on from Martinus, CT1IQI.

I first configured the amplifier for network access. I tried using the WiFi Interface but that had intermittent hissifits  so I connected it to my wired network using a STP patch cable (CAT6) and configured the Network interface of the RF2K-S through the menu system.

From the main screen select [MENU] :

and select [Network] [LAN] or [WiFi] :

The default will be DHCP however, I would advise to use a manual IP-Address. It does make it easier in finding the devices IP-address (YMMV). And should the DHCP reservation time out, it might assign a new IP-Address to the amplifier causing future connection issues.

NOTE: If you are using DHCP you'll have to search for the IP-address in your router/dhcp server address table. Make sure to have the address reserved, i.e. map the address as a static address. Consult your manual on how to do so (it would be nice it the amplifier would display its own LAN/WiFi MAC-Address, this would make finding the DHCP assigned IP-address a lot easier)

I've setup my router to act as a Name Server, as such I've also populated the [Name Server] field. (Again YMMV)

To test if the amplifier is reachable from your PC use the ping command. 

hw@rapi4:~ $ ping -c 3 rf2k-s <-- use your amplifiers IP-address (ping 1.2.3.4)

PING rf2k-s (192.168.1.11) 56(84) bytes of data.

64 bytes from rf2k-s (192.168.1.11): icmp_seq=1 ttl=64 time=0.476 ms

64 bytes from rf2k-s (192.168.1.11): icmp_seq=2 ttl=64 time=0.429 ms

64 bytes from rf2k-s (192.168.1.11): icmp_seq=3 ttl=64 time=0.423 ms

--- rf2k-s ping statistics ---

3 packets transmitted, 3 received, 0% packet loss, time 2004ms

rtt min/avg/max/mdev = 0.423/0.442/0.476/0.023 ms

Having finished setting up the Network interface of the amplifier it's time the control Interface.

Select [Interface] and select UDP as the Default operational interface:

Now select [UDP] to select Port 12060 (the default)

and check Listen to active radio.

Now onto the Radio Control Application. In my case that is Commander from the DXLAB suite of applications. 

NOTE: I've been told that Log4OM is capable of the same feat however, I've not tried this.

In Commander open the Configuration Panel and select <Net Serv> from the [General] tab:

which brings us to the UDP Network Service window.

We add our amplifier IP Address and Port number as shown and enable the UDP Network Service. The New transceiver (Xcvr) Delay is set at 10, you might like to experiment here if you are using a WiFi connection.  

That's it for the configuration. For operation you would make sure that you select UDP through the UNIV menu.

Profiling my antenna using WSPRNet

First things first, if you have a beam or more than one, on a mast or tower that nearly reaches the sky you might want to move on as this is more a process for us mere mortals that live in suburbia and have to live with a piece of wire.

 

I've been trying to get a "feel" for "how my current antenna is performing at my current QTH"! The antenna in question is a 40m Delta Loop, which is slopping from the roofline into the backyard. Now I can model the antenna with one of the many Antenna Modeling programs and using the results I can evaluate if the antenna will perform to my satisfaction. However, it is a model and it will show the antenna to work in an environment that is not indicative to the real environment.

So the next best thing I've done in the past use data from my logbook to get an understanding of the performance of my antenna. However, all this can be speed up these days in using WSPR. I'm not here to explain how WSPR works, except I will reuse the description given by the good folk at WSPRNet.

The Weak Signal Propagation Reporter Network is a group of amateur radio operators using K1JT's MEPT_JT digital mode to probe radio frequency propagation conditions using very low power (QRP/QRPp) transmissions. 

So basically I've setup a WSPR receiver over a period and reported the data to WSPRNet. I could also store the data in my own database, but why reinvent the wheel. Having all the received station data available we could now download all of the data and run it through a graphing/data analysing tool like grafana, gnuplot or Octave.

But why if we have a first class tool written by VK7JJ online directly getting the data from WSPRNet so I don't have to bother with anything else but look at WSPR ROCKS!

As I mentioned I setup a WSPR receiver to monitor the Amateur Radio WSPR frequencies from LF (136kHz) to end of HF (28MHz) and send the collected results to the WSPRNet. I then use the WSPR rocks website to filter out the Band of interest, use the biggest amount of data sets (limited at 5000), select unique calls and select an appropriate time frame.

Lets use the above selected dataset. Initially, the data will be displayed as text first. And to graph the dataset I select <charts> and then <SNR compass>. The result can be seen at the below graph. It is the result from all unique calls which my WSPR receiver heard over a  three (3) day period on the 20m WSPR frequency.

 

I can already see that my antenna is favoring only two directions, more than any other direction.

The question is, can I be sure?

It sure is a good start to visualise the real receive pattern but there is another dataset we can check and then compare it to my recorded dataset. That dataset is the <everyone> dataset. We can select that dataset for a comparison check by setting the <RX call> value (currently set to vk5hw) to everyone. And voila we get ...

This tells me that from 0° to 360°, i.e. around the globe stations where reported for the same time period. Comparing this graph with the graph from my dataset confirms my initial observation. It shows that I have two good and one sort of ok direction were the antenna is performing. The directions between 60° - 110° and 270° - 300° are pretty good. 315° - 25°, well I do receive signals but it seems to be a struggle. There are additional single signals around the 240° and 135° mark but they would be the exceptions due to ... maybe enhanced propagation wich I could find out with a propagation tool (Voacap or GWPS). Now there could have been por or no propagation between me and all those other stations. But even so, I'm confident that this is a good profile of my 20m receive capability at my QTH with the current (40m Delta Loop) antenna. 

There might be the ocasion opening that might give me a better path into those regions which I've received no signal from but those are more likely the exceptions and not the rule. 

Since antennas are a reciprocal passive device, meaning they work the same on receive (RX) and transmit (TX) I'll know which areas of the globe I'll be making easy contact to and were I would have a difficult time to work stations. 

So this is the profile for 20m on the 40m delta loop, and since I use the antenna for 40m, 20m, 15m and 10m as a TRX antenna I need to run profiles for at least 40m, 15m and 10m. Of course I'm also interested in the bands that I only use the antenna as a RX antenna so a few more graphs to compare. However, all I wanted to show is how easy and quick it is these days to profile, i.e. get a good feel, for ones antenna installation at ones QTH. 

Well, most of this is not new to me, but it confirms that I could have done this in three (3) days rather then in 24 month. That's how long it took me to to get to the same conclusion by operating FT8 and SSB from this QTH.