A model of my 40m Delta Loop

At my QTH it is rather difficult to have dipoles strung up at a decent height. As I have had quite good success with horizontal loops (see my old Lazy-D) I decided to install a slopping Delta Loop at this QTH. From what I can tell the antenna is working quite nicely and I am able to make the radio happy with the internal tuner on the following bands, 40, 20,17,15,12,10 and 6m. Now it is not a WONDER antenna however, it does the job for me (YMMV).

Installation details:

• Feed point is 14m above ground (1.5m hockey stick above roof).
• The end corners are about 5m above the ground.
• Feedline, the first 3m are a commercial Ladderline (labeled 450Ω but it might be closer to 390/400Ω), then 20m of LMR-400, 3m of RG213 and 0.8m of RG8 from the ATU.
• The antenna is strung to face towards the East, at approx 110°.

As I also use this antenna as a RX-antenna for ELF/VLF I have removed the BALUN and only use a few chokes on the coax-feedline. Below is a drawing of the antenna.

40m radiation pattern:

As we can see, nothing really to talk about it. Pretty good for NVIS and with a bit of luck, e.g. very good to excellent propagation I might work a little bit of DX.

20m radiation pattern:

On 20m we can see two lobes. One to the East with a nice bit of low angle gain into the East which would help to work short path into the Americas and long path into Europe. However, the high angle lobe seems to be also quite good.

17m radiation pattern:

Even though the VSWR on 17m is not that great, the inbuilt Auto Transmatch (ATM) manages to get the SWR down enough for the Radio and Amplifier to be happy. Losses due to SWR are low enough and don't cause any issue. Looking at the pattern we can see that we have very similar coverage as for 20m. And, as it is for 20m, there is still a high angle lobe.

15m radiation pattern:

Now on 15m we can see that the high angle lobe has disappeared and that there are quite a few usable lobes. There are East and West lobes, with the East lobe quite low and strong, but also quite narrow. Additionally the North and South ones are quite broad with a nice bit of gain.

12m radiation pattern:

As for 17m, the VSWR on 12m is not that great. However, the ATM is able to keep the Radio or Amplifier happy. SWR losses are nothing to worry about. The radiation pattern is very similar to the 15m pattern with noticeable nulls in the North and South lobes. Again, lots of good gain into the East and reasonable gain into the other hemispheres.

10m radiation pattern:

Unfortunately on 10m the pattern starts to create lots of lobes with good low angle gain lobes into the East and West. However, the coverage for North and South is not that great. Lobes are high and not much gain in them.

6m radiation pattern:

Well 6m, what can I say. We can see quite a lot of narrow lobes albeit with good gain.

And yes, I can use the antenna on 6m and have made contacts into Western Australia (VK6), Northern Territory (VK8), Queensland (VK4), New South Wales (VK2) and Japan (JA) however, they have been far and few.

The antenna has been modeled with real ground (poor) to give me an indication of what I can expect at my QTH. However, it is not a true indication of the actual radiation pattern, there is a House behind the antenna (to the west) which will change the characteristics of the antenna performance especially into the westerly direction.

As with every antenna the impedance (Z) changes with height, soil conductivity and of course surroundings. This will dictate what type of Feedline and or BALUN one would/should/could use, there is no silver bullet. I do use an Antenna Analyser (VNA) to learn what the actual Antenna System (Antenna + Feedline) Z at my installation is, e.g. what my ATM would be presented with. This does help me to use what feedline and/or BALUN etc. I would use to configure the antenna-system to my requirements e.g. adjusting the antenna at a frequency of 7.2MHz to create easier matchable impedances for the additional Bands/Frequencies I would like to operate on.

According to my previous model of a Delta Loop used as a Horizontal Loop (LAZY-D) the Z was approx. 100 +j10Ω at resonance, which would mean that a 2:1 BALUN would be the right choice to get a good 50Ω match. 

Compared against the previous installation, this model tells me that I could except the Z to be > 200Ω which would indicate that a 4:1 BALUN would be needed to get a good 50Ω match. 

If you'd like a bit more information on Delta Loop antennas, a good educational read is the work of W4RNL (SK). His notes on Delta Loops can be found here. 

So to wrap it up, the block does not lend itself for the installation of a multiband dipole type of antenna (G5RV or ZS6BKW) so the next best thing for me was to grab something out of my box of tricks and go back to an old, but proven concept.

I didn't really wanted to add an VSWR prediction chart but due to multiple requests, here is a quick SWR plot of the modeled antenna:

Here are some SWR plots before the removal of the BALUN. And a view of how the antenna performs can be found here.

Excessive Single Side Band Transmission, also know as ESSB or eSSB.

There seems to be an increase in the transmit bandwidth range for SSB communications, which traditionally operates within a narrow-band of approximately 3 kHz. Now if we go with a 3 khz “Voice channel” for Single Side Band (SSB) then the Transmitted Bandwidth, let's call it the TxBW, should fit into the range 0-3000 kHz.

However, I’ve noticed more and more operators use a TxBW of 4 kHz or more. This is often referred to as Extended Single Side Band (ESSB) which I have seen to extend in some instances even to 5 kHz and more. The claim to fame is HiFi Audio.

Now Amateur Radio is an experimental hobby, so this, on the surface, shouldn’t irk anyone, shouldn’t it? However, I frequently encounter ESSB operators on 20 and 40m talking to operators who have not modified their station for ESSB communications, i.e. a station with a TxBW 5 kHz to a station with a 3 kHz Receiver Bandwidth, lets call that RxBW.

So what seems to be the issue?

Let's say a QSO is conducted on 14.229 MHz, one operator uses a TxBW of 2.9 khz and the other uses a TxBW of 2.4 kHz. Signal are good with about S7 both ways. Since this is conducted using the Upper Side Band and, if we apply a Voice Channel spectrum of 3 kHz the used frequency spectrum for that QSO is from 14.229 – 14.231 MHz (not quite but let's stick with 3 kHz). Stations operating on 14.232 MHz should not have any issues operating. However, let's assume one of the operators is operating at a TxBW of 5 kHz. This situation would infringe stations operating on 14.232 MHz quite badly. Another example would be if a DX station is calling on 14.232 MHz and I would like to work that station. However, I will be unable to do so due to the excessive TxBW of the ESSB operator (14.229 - 14.234 MHz). 

Anyone see an issue here? Well, I do! However, the question is does the ESSB operator see the issue? From my experience most ESSB operators do not.

So why use 5 kHz TxBW whilst conducting DX contacts. Aren't we trying to share the limited frequency spectrum between all Amateurs? There is certainly NO benefit to the station receiving the ESSB station. 

Frequency spectrum during “openings” are crowded and transmitting with a 5 kHz TxBW during these opening does not show any courteousey towards other spectrum users.

The above shows an Australian Operators transmission with a TxBW of  5 kHz and the DX station using a  less than 3 kHz “Voice Channel”. I will assume that the DX stations RxBW would not be more than it's TxBW.

NOTE: I’m referring to the TxBW and not the Intermodulation Products (IM) or “splatter”, e.g. the light blue “hair or whiskers” on either side of the signal, which are obvious related but are not discussed here.

This is even more frustrating on the 40m Band, as there are more an more local stations operating with a TxBW of greater than 4 kHz. 

Now Amateur Radio is an experimental hobby and experimenting with a TxBW > 3 kHz does fall under this category. So, yes I believe in experimenting but this is not experimenting, this is not understanding the implication of excessive TxBW. And believe me I’m all for experimenting. However, I am quite happy with a 2.4 kHz well balanced audio TxBW which would influence the use of an appropriate RxBW.

Additionally I believe that these operator would not know how much "real" power they are transmitting. If we talk about 400W PEP, then the average output power would be rather LOW.

NOTE: I also observed that these type of operators seem to drop their TxBW to 3 kHz during Contests!?!  Yet they seem to believe that during crowded DX sessions it is OK to use 5 kHz or more TxBW. Isn't that a bit hypocritical?

Since Amateur Radio is a self regulating hobby it might be about time to add a frequency spectrum for those inclined to use ESSB. I believe this has been done for certain other modulation schemes (AM/FM/DIGITAL).

ICOM IC-7610 S-Meter Tracking

Having been checking the S-Meter for my prefered software solutions  (SDR) I thought it might be a good time to also (re)check the S-Meter in my ICOM IC-7610. The setup is the same as for the previous two checks. Below is the result of my checks for my IC-7610. A quick graph of how well my ICOM IC-7610 S-Meter is tracking using the IARU Standard of 6dB steps (6dB/S-Unit).

Setup:

• Signal generator: XG3
• Level: -34.8dBm @ 13.8V
• Att: HP-355C & HP-355D (38dB for approx. -73dBm level)
• Frequency: 14.175MHz

Result:

Table 1

Graph 1

The graph shows a pretty linear S-Meter for the IC-7610 down to S4 with a 6dB step per S-unit. The above graph is based on the measurements at 14.175 MHz (20m) with the PreAmp off. However, enabling either preamp we can see from Table 1 that the measurements deviate quite a bit. So for the times that I'd use either of the preamps I need to do a bit mental arithmetic. My measurements show a 6dB increase for PreAmp 1 and a 10dB for PreAmp 2. But please note, even though the data in Table 1 looks spot on, the measured values are rounded up or down to the nearest integer. However, we are talking about an Amateur device not a professional Field Strength Meter. So I'm quite happy with the result.

Here are some older 40m graphs.

Graph 2

Graph 3

Graph 4

Below is my cheatsheet for S-Unit vs dBm vs µV.

Graph 4

CLICK on a graph for a better view.

NOTE: Even though the above graph is displayed with 3dB steps, it is 6dB per S-Unit!

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: