A quick Standing Wave check on my antenna system (baselining)

A quick check of my antenna systems SWR (VSWR) tells me that I should be able to use the antenna system on five AR-Band without to much trouble. However a few quick note before heading of to the actual task.

I'm not going to talk about impedances, reactance or admittance. I'm simply checking the SWR to get a basic overview of the overall antenna-systems ability to be used with with my transceiver and/or being able to use a small ATU (Antenna Tuning Unit) to pretend the SWR is "good". It shouldn't really be known as an ATU as it really isn't tuning the Antenna. It is a device using lumped circuits (L's & C's) to present a match to the transceiver output stage. Which is not a constant 50Ω at any of the AR-Bands either. So this quick check of the SWR is enough information which tells me all I want to know (at this stage). 

An additional note. You might have noticed that I always say check and checking the SWR! Well I've never seen a SWR meter that measures SWR (how would we be able to measure a ratio). SWR is not a measurement it is a calculation! Generalised, a VSWR (Voltage Standing Wave Ratio) check is a Voltage measurement of the forward and reflected voltages at one frequency. From those two values the SWR is being calculated. 

So onto the antenna, it is a 40m horizontal loop, attached to two TV roof standoffs to clear the edge of the roof and than slopping into the backyard to a height of 2.3m 5m above the ground.

It is feed with about 3m commercial 450Ω  ladderline to a 1:1 current balun. The rest of the feedline is about 20m of LMR400 and a short run of RG213 and RG8X for the interconnections between the ATU, AMP and the Transceiver. The feedline is heavily chokes with homebuilt chokes.

Measuring from the 213 I'd say I've got 23m of 50Ω feedline to the balun and about 3-4m of 450Ω feeder. My guess is (but I should really measure it) that I don't have to worry about too much loss through the feedline on the four HF-Bands and even on 6m the line should not be to lossy (not sure about the BALUN though, more checking/measuring required).

So how does the SWR look like. (NOTE: If I talk about the SWR from now on, I'm talking about the antenna-system SWR and not the antenna SWR.)

I do not use an inline SWR meter for this purpose, the inline SWR meter is, and that is my believe, only good for monitoring if a change in the antenna system has occured. 

For this tasks and long term comparisons (baselining) I'm using a RigExpert antenna analyser. 

Basically I'll check from after the ATU, i.e. from the end/beginning of the RG-213 upto the antenna.

Below is a picture of the result.

It only displays the five bands that have a reasonable SWR. So let's zoom in a bit.

1. 40m

Bit low in the band, my aim was 7.100 but I thought this wasn't to bad straight of. It shows the VSWR at 40m is good to very good, with an average SWR below 1.5:1.  

The other bands have their best  VSWR outside our allowed frequency allocations. And experience tells me that I'll be able to use my ATU to present an acceptable SWR to the transceiver for proper operation of the output-stage. But even on 40m I should use an ATU to keep the transceiver/amplifier happy as the above 40m SWR plot clearly shows.

2. 20m

On 20m the situation is not as bad as it looks, best SWR is around 13.9MHz. But we also can see that the SWR is not to bad across 14-14.35MHz. With max SWR of less than 4:1 at 14.35MHz. Yes, looking at the Z, e.g. the impedance, I would be able to see if my ATU would be able to tune that. But for now this is all I need.

3. 15m

On 15m the situation is very much the same.

4. 10m

On 10m however, the SWR bandwidth is quite broad and in most cases I'd not need to use an ATU unless I go into the FM spectrum.

5. 6m

And last but not least the bonus Band, 6m. The spectrum I'm mostly interested in, 50.1-50.4MHz has a VSWR greater than 2:1 and would need an ATU to keep the transceiver happy.

Now all this means is that I should be able to operate on these bands without to much trouble. The ATU's build into the newer type of Radios and Amplifiers with their 3:1 tuning range should find a suitable match without breaking sweat. And, my trusty old YAESU FC-901 ATU is able to tune the four HF bands easily without getting warm at 400W.

So now that I have this data "stored" I can say that I have baselined my antenna system. I can now refer back to this data to see if, over time changes have occurred.  

Last thoughts:

• For an antenna SWR the SWR should be checked at the antenna itself rather than at the end of the feedline. The feedline will load the antenna and create an illusion of having a better antenna SWR.
• To fully understand your antenna-system, feedlines (transmission lines) should have their attenuation (cable loss) measured or calculated (length measurement tape-measure  or TDR).
• Knowing the above, one can calculate the SWR at the antenna feedpoint.
• I would not use an inline SWR Meter for any of the above measurements however, using an inline SWR-meter is good insurance policy because connection problems usually show up as SWR spikes which can quickly be seen on those type of meters during operations.

My transmitted signal analysed

 A quick look at a spectrograph to analyse my transmitted signal.

Setup:

Transceiver : ICOM IC-7610

Power       : 108W

Antenna     : 500W dry dummy-load with 40dB tap

Modulation  : SSB (LSB)

Audio setup : see here

Receiver    : RF-Space SDR-IQ

Software    : SpectraVue Ver.3.39

IF-Gain     : +6dB

RF-Gain     : -20dB

Lets analyse the signal.

The grey section shows the receiver audio bandwidth (BW), i.e. the SSB RX filter bw or the CHANNEL BW. 

The black area is the so called Video BW, in this case a 30kHz view of the spectrum. A frequency spectrum display from 7.160MHz to 7.190MHz .

The green line is the real-time capture and the blue line is the in-time capture, the memory of the previous capture. 

The display also shows some vertical lines with a distance (spacing) between two lines of 10dB and there are also some vertical dotted lines which are 3kHz apart. Additionally I have applied "smoothing" to quieten the real-time capture. (I'll show the same signal without smoothing further down below) 

Now let's look at the BLUE line (the Sideband envelope), as that line dipics my previous SSB transmission. The top of the signal is about -59dB (S9+14) a reasonable strong signal. We can also see that the width at the top of that line fits into the grey, the 3kHz bandwidth marker, and is about 2.9kHz wide (100-3000Hz). We can also see that the signal slowly spreads out towards the bottom, down to the about -90dB from were it then spreads between a bit more quickly to 7167.8kHz and 7182.8kHz. Since the carrier frequency is at 7175kHz, we can deduce that the signal is spreading -7.2kHz and +7.8. 

Struth, what a crappy wide signal ! 😇

BUT, wait! The WIDENING of the signal starts at approximately at -91dB (S6). Which would mean that from the peak of the transmitted channel BW the signal is "clean" for about 32dB. Now that is a pretty good NON pre-distorted signal. 

The following table shows how the signal from about the -90dB mark spread very quickly, but also drops very quickly in signal strength. 

Frequency	Signal Strength		Frequency	Signal Strength
7169kHz	-100dB	S4.5	7169kHz	-100dB	S4.5
7166kHz	-114dB	S2.2	7181kHz	-114dB	S2.2
7163kHz	-124dB	S0.5	7184kHz	-124dB	S0.5

NOTE: S-Value steps are in 6dB

This does help me to understand how wide my signal really is and when and how I would cause channel interference based on a 3kHz channel spacing. 

Below is the same signal without smoothing.

As we can see it is very easy to check our own transmitted signal. The requirements are not that strenuous. A  tap, dummy load and a SD-Receiver is all that is required to not only check our transmitted audio, but also our transmitted signal. Here are a couple of tap's that are easy to replicate, a 40dB and a 50dB tap.

A Splitter/Combiner

A while back I build a combiner for some two tone tests on some older type transceivers. Well the transceivers have now gone and so I found new use for the combiner as a splitter. 

The combiner has pretty good port isolation of over 50dB and an insertion loss of about 6dB. To test some of my SD-Receivers I use the splitter to divide the receive signal from the antenna and feed two SDR's so I can compare rx-prowess. 

The toroid I used is my trusty old workhorse, a Jaycar Model LO1230 (with the dimensions of 18x10x6mm) which has very similar characteristics as Mix 43. A FT50(A)-43 might do a slightly better job (maybe), but the LO1230 is available locally at a reasonable price and does the trick nicely. The resistors are 50Ω resistors (green gold white white yellow) (I have a few left overs from other projects) but a 49.9Ω 1% resistor should do the trick as well. 

Now, the 100nF capacitor is more or less an insurance policy, it is used as a DC blocker. You could leave it out if you so desire. I've put 12 bifilar windings around the toroid and that's it. Nothing to elaborate. 

Here is a quick sketch of the unit:

And here are some measurements of the unit.

1. Attenuation:

2. Port isolation:

As can be seen the isolation is very good from 80-6m (3.4MHz - 50MHz) but is still good enough for rx testing below 3.4MHz and above 50MHz. I might test again to see what the specs are for below and above frequencies. Anyway as it is it works for me at the current use, which is being used as a splitter and not a combiner.

3. Photo of build unit:

I currently have the unit setup for my SDR-IQ and RSPdx to compare rx prowess at ELF, VLF and HF using SDRConsole, SpectraVUE, SDRuno and HDSDR. The 6dB attenuation is only a problem at the higher end of the spectrum which I can compensate with an assortment of low noise amplifiers (LNA's) from Minicircuit and homebrewed units.

Listen to the Music

Listen to the music, but not on SSB with a 3kHz bandwidth. What I mean is, listen to the Amateur Radio Bands, and you will quickly understand what I'm talking about. Some of the audio signals on our bands are appalling. Even worse are some of the reports that people are relaying back to these poor operators.

It's worth noting that many amateur radio operators strive to have a clean and pleasant signal. However, both the amateur radio community and society, in general, have become non-constructive regarding any form of insights or criticism. Therefore, the information below may help some operators check their transmission quality.

A little bit of research on the internet reveals that the human voice contains frequencies ranging from about 100Hz to 8000Hz. However, only the energy between about 300Hz and 3800Hz contributes to the intelligibility of speech. Vocal content below 400Hz provides "body" to the voice, which is great for singers and radio announcers. Speech content above 3000Hz provides presence and can aid communication, to some extent. However, the added bandwidth can introduce noise and other complications.

In my opinion, in a Single Side Band (SSB) communication system, it's crucial to achieve the highest Signal-to-Noise Ratio (SNR) at the receiving station under strenuous propagation conditions to get the message across. To achieve this goal, we should transmit the portion of the human speech that affects articulation the most, which research has shown to be the spectrum between 300Hz and 3300Hz.

These bandwidth limits have been established in the days of long distance telephone systems and have served the telecom industry of our world quite well.

The standard SSB TX filter in most SSB transceivers is 2.7kHz wide, and a well-adjusted SSB transceiver has this filter aligned so that it will pass audio between 300Hz and 3000Hz. Since SSB transmitters are peak power-limited, transmitted energy below approximately 250 Hz will show power on the power meter but will not contribute to the articulation at the receiving station. However, these days we often see signals with a "power-grab" dominating the bands. Many operators focus solely on increasing their power output, resulting in signals that are difficult to copy and interfering with other spectrum users on either side of the selected channel. These bass-heavy signals can swamp the AGC in a receiver, creating a low-frequency rumble that is unintelligible and potentially causing issues for other spectrum users.

Fortunately, with the availability of publicly accessible Web-SDR systems, it's now possible to monitor one's own transmissions quite easily. 

The way I do this is however, slightly different as described below. 

To set up a transmission check, I first record a test transmission and play it back through the transceiver which is connected to a dummy load/antenna. While transmitting the recording, I listen to the signal using a second receiver (in my case, an SDR-IQ) to adjust the TX-audio profile, including the TX Bass and TX Treble on the ICOM, MIC gain, and compression.

When adjusting compression, I make sure to adjust the MIC gain so as to avoid the compressor pumping up background noise during speech breaks. By listening to my own transmission, I can tailor the audio characteristics to ensure that all transmitted power remains inside the available SSB channel. This is particularly important for QRP stations or foundation license holders, as losing just 3dB to either side of the channel means that only a quarter of the peak power is transmitted inside the wanted SSB channel, potentially making it difficult for the receiving station to copy the signal.

Below is a display of a test I conducted to get a more balanced audio profile. The LSB signal within the top of the waterfall in the below picture is showing emphasis on the low end of the audio spectrum. Visible on the bright red right hand area. Below this signal we can clearly see that I have selected/created a more balanced audio profile.

Analysing those signals, we can see that the first signal has quite a lot of emphasis on the lows, at around 100-400Hz (on the right the big red line). This makes the signal sound rather bassy, and although it shows a lot of power on the power meter, it is not overdriven (like most of the signals on the bands today). 

Operators who prefer to use wide-open audio filter might find this sounds okay. But for longer distances, were the receiving station only has a bit better than marginal reception, say S5, it would be difficult to copy.
The second signal shows much better-balanced audio and I would classify this as very good communication audio. However, the bandwidth of both signals is approximately 2.9kHz (100-3000Hz) which is still in the 3kHz channel bandwidth. I believe that the bottom signal would still sound rather nice at a 2.6, 2.4kHz bandwidth even in 2.1kHz with a lot less noise bandwidth this signal would still sound Q5.

Oh and ESSB enthusiast find my view of the use of narrow band audio for SSB harrowing. However, it would be nice if these OM's would find a space in our limited spectrum were they would NOT interfere with low power stations that they might not hear.

I've been seeing quite a few ESSB operators on 40m clobbering small signals due to their inability to hear those stations and make it difficult for others to make the contact with those stations. 

Also, I don't believe that ESSB should be used during a contest where bandwidth is limited, not even by a contest station.

Receiver gain setup

I always setup my receiver(s) with just enough attenuation/gain to make sure that the AGC only acts on the signal I'm listening too. 

I have the preamps switched off on all band from 20m and above (14MHz and below). Depending on the band conditions I either use the build in attenuator or the RF-gain. Below are the steps that I use to achieve receiver bliss.

1. Record the S-meter reading of the band noise. I tune off the signal I'm listening to and note the S-meter reading on band noise alone, for example the S-meter is reading S5 (a noisy day).
2. I now apply attenuation until the S-meter reads as little as possible. On the IC-7610 I can select the attenuation in steps of 3dB. If you don't have that ability you can achieve a similar outcome with the RF-gain knob as well. 
3. Next I tune the desired signal in again. The result is that now the band noise will not stimulate the AGC into action, i.e. the AGC will now only operate on the desired signal.
4. I now have selected the sweet point for the receiver for the current band conditions.

The result is a very quite receiver which is very pleasant to listen to.

NOISE COUNTER MEASURES, or how to make sure we can hear those new QRP stations!

I did live in a fairly, Amateur Radio Operator populated area (Canberra ACT) with quite a few Amateur Radio Operators close by. Some of them with the same transceiver outfit as me. There were of course slight differences. For instance, my antenna arsenal then comprised of a Multiband Vertical (Cushcraft R8), 40m horizontal loop, non-resonant dipole (ZS6BKW), a 1/2λ 80m inverted L, (RX/TX 80m and RX down to 200kHz) and then a few RX only E-Field and H-Field antennas (MiniWip clone and a Hermes Loop). Whereas most had rotary dipoles on 40m and some even had 2 element beam (Yagi/Uda) antennas. 

And yes, my QTH was on a small suburban block surrounded by houses, which were positioned higher than my Antennas at the back and to the right. To the left they started to climb up gradually and the only real take off was into the NNW at about 280 to 320 degree.

Yes, I've been lucky to be able to get these antennas into the air (I do do dishes and other chores around the house which does give me AR-brownie-points). 

Anyway, what I've noticed is that some of my local Amateur Radio colleagues don't seem to hear as well as I do. The complaint is about NOISE i.e., a noisy receiver.  I do understand that there are differences in antennas, antenna patters, antenna angle of radiation etc. but, most of the time those stations are being heard a lot better than me. However, when it comes to receiving, I seem to be able to hear station on the end of the contact a lot better. Well, It can't be the radio, as some actually have the same radio, an ICOM IC-7610. 

So what could it be? Why would I be able to hear stations a lot better? And I mean most often a lot better. (It could be that I have a better HSP with more HIPS 😏)

Maybe it is the way I use my receivers reception improvement arsenal and so I thought I'll share the way I use the tools my receiver provides to improve my listening pleasure.

So lets have a quick look at the way I conquer some of the noise.

Please note, that these are some of the things I do to help me overcome QRN and even some QRM. This is not a blurb about technical specs, even though I might throw some into the mix. This is more a HOWTO get the best SIGNAL to NOISE (SNR) performance out of your system, i.e. the system made up of the receiver/transceiver, the antenna and not to forget the antenna cable. Being able to receive and understand a station that does not move the S-meter up to the S9 point but still has reasonable good recovered audio quality even if the signal strength is as high as the band noise floor.

First up a disclaimer, I do not talk about the "OH NICE SIGNAL 59+20", sounding like John Laws and are > 3 kHz wide, no I'm talking about stations that are in or just above your received noise floor. And second, I refer to Single Side Band (SSB) but will show the effects on a CW signal to make it easier for me to show the effects.

We know that our receivers have BIG EARS. For instance the Minimum Discernible Signal (MDS) of my ICOM IC-7610 starts at about -122dBm and goes to over -140dBm [1]. Basically what that means is, that the radio is capable of hearing the proverbial fly fart. 

I would like to see the ambient noise floor at my QTH go that low but according to ITU P.372-12 the noise floor at my QTH should be about -91 dBm at 7 MHz (S6) (Note: an accurate S-Meter is required to confirm this). At the new QTH, here in VK5 land it is slightly better, by about 9dB.

Which is still a far cry away from -122 or even -140 dBm of which the IC-7610 is capable of achieving (sorry about the technical digression).

To show you what I'm talking about I've been taking some screen shots which show what can be achieved by applying the following, let's call them receiver-improvement-tools, to improve our receiving pleasure. The setup for the demonstration comprises a SDR-IQ withand the following software SpectraVue Ver. 3.39 and SBSpectrum Ver. 1.31. 

To have a steady signal I'll be tuning the radio to our local NDB (ground wave) at this frequency the noise is still high and the signal will be at a constant strength for the duration of the test. This makes it easier to show the effects of the applied countermeasure. 

So here is a list of the Tool Set I've been talking about.

• RF-GAIN control
• RX-Attenuator
• AGC
• RX-filter bandwidth

If we apply any or all of the above appropriately we'll be able to dig out signals that are difficult/marginal to hear/understand. What we are doing is what is know in professional circles as the improvement of the Signal to Noise Ratio (SNR). It does not mean that the signal strength will increase, most likely the signal strength will be lowered. However, not only the signal strength will be lower but also the received noise. And, this is the aim of the game,  if we apply our toolset appropriately we will reduce the noise level more than the received signal! And as such we will have improved our SNR.

Let's start with our receiver bandwidth (RX-BW), some call it the channel bandwidth, e.g. the frequency span the receiver is listening too. Receivers have a basic RX-BW of about 3 kHz. And most Voice transmissions are with a 2.8kHz transmit bandwidth (TX-BW) (yes, yes I did say most).

Now if we look at those number we can see the we already have 200Hz unused RX-BW and this 200Hz is filling our receiver with noise (RX-BW3000-TX-BW2800=200Hz of noise) Imagine if the transmitted signal would have a TX-BW of 2.4kHz and we would receive the signal with a 3 kHz RX-BW. We would now receive 600Hz of additional noise. To improve the quality of the signal we would need to get rid of the 600Hz of noise. 

In the olden (Golden?) day's we added X-Tal filters to limit the ingress of additional noise (a quite expensive exercise let me tell you). However, this is were the new breed of SDR's shine, they use "software" to do the filtering and some of those software filters are exceptionally good. Additionally they are very flexible, with soft or hard skirts etc. You'll be able to adjust the RX-BW quite easily to adapt to the transmitted signal.

So by adjusting the RX-BW to the TX-BW we would improved the SNR by 600Hz.

On a good receiver S-Meter, one would be able to see that the noise floor has dropped and the signal has gone up. 

Let's have a look how that would look in real life.

The grey area is the noise that we are receiving. Looking at the bottom CW signal we see that we can see (hear) it but it is quite buried in the noise. Taking away the noise by limiting the RX-BW we are able to see that the signal becomes more darker, almost black. It is now popping out of the noise and listening to the signal it is more audible, e.g. clearer and more intelligible. If we widen the RX-BW again it becomes clearly visible that the signal loose's  its intelligibility, as it is fading back into the grey again (picture below).

For me reducing the RX-BW is one of the most effective ways to improve the received signal quality. Even if I receive a signal that does not limit its TX-BW to say 2.8kHz I always run 2.7 or even 2.1kHz RX-BW on SSB. I even go as low as 1.7 or 1.5kHz RX-BW if the going gets tough but that has mostly to do with adjacent channel QRM. 

If you tune above 7.2MHz at night you will find some US Amateur Radio Operators there between the big AM BC stations. And those narrow filters make it possible to hear those station without to much interference from those potent signals.

What we have done is we have limited the receivers SIGNAL+NOISE ingress e.g. we've improved the SNR. The net effect is that the SIGNAL we are interested in, SOUNDS clearer/louder.

 

Another tool in our receiver-improvement-tool is the Automatic Gain Control, the AGC. Most modern Amateur Radios have the ability to adjust the TIME CONSTANT (ATTACK TIME) of the AGC.

The below picture shows the AGC disabled and then enabling the AGC, the noise disappears and the signal pops up. It is worth while playing around with the AGC time constant. This is a bit of an art form and it is quite different between radios and the design of a radio. I have three different settings on my radio for different noise events/modes. I have a slightly faster AGC recovery time for thunderstorm/lightning QRN then I have for quite band conditions on 10m. Also I have different timing setups for different modes (SSB, CW, DIGI).

Switching the AGC off and riding the RF-gain can also improve our listening pleasure. Below you can see me adjusting the RF-gain manually (this is called riding the RF-Gain) to bring the signal out of the noise. However, as you can see from the above picture, a proper adjusted AGC does do a better job than I can do.

The next picture show a combination of AGC and manually adjusting the RF-gain.

I wish it would always be that easy.

Instead of ridding the RF-gain, most radios have the ability to add predefined attenuation. The below picture show similar results as using RX-BW limiting and predefined attenuation switched in and out.

Below is a good view of the AGC in action. As soon as there is no signal, the AGC increases the gain (darker grey), but as soon as the signal shows up the AGC reduces the gain enough for the signal to pop out of the noise.

So, as you can see we have a great arsenal of tools available to BETTER our receivers ability to get the desired signal out of the noise, or to phrase it more appropriately, to ease the HSP between our ears to only work on the SIGNAL and not needing to apply filters to remove the noise (remember the HSP has limited HIPS).

Please remember that I used a CW signal for display purposes only, this will work equally well for SSB and even for some DIGITAL modes.

On 7 MHz (40m) and below I use between 9dB and 24dB attenuation as atmospheric noise levels are high on these bands. Start with whatever you feel comfortable with. Next I'd setup the filter bandwidth to remove the higher pitched noises, the noise above 2.4kHz and then I adjust the filter to cut out the low rumbles, the noise below 100 kHz. My RX filters are set at 2.7 kHz, 2.1 kHz and 1.7 kHz for SSB, low cut at around 100 - 200 Hz for example, my 2.1 kHz filter bandwidth is setup as 200 - 2300 kHz. And last but not least, adjust the AGC to your liking. My preference SSB AGC settings are Fast 1.2, Mid 2.0 and Slow 6.0.

The AGC, RX-gain and RX-attenuation are basically controlling the overall system gain, which does includes the gain from your Antenna System (Antenna, Cable, ATT, LNA etc.).

The RX-gain/attenuation values will be different for a lot of situation it depends on a lot of factors i.e. the mode of operation, what antenna is being used, the frequency of operations, the operator mood, the time of day, band conditions etc. etc.

However, as you get more and more familiar with your radios rx-tool-set you will not only get more and more pleasure out of your receiver (station), you will also manage to finish more contacts with ease.

Remember, you will need to play around with the setting until you find a setting that sounds/feels right to you. The above are setting that work for me and should only be seen as a guide. Your environment, radio, antenna, HPS and HIPS are different. 

Let me mention a few more tools that some of the radios provide or are external items that would improve our listening pleasures. An additional AF filter (Equaliser) can help in reducing noise, Digital Noise Reduction Systems (NR), which most newer radios have built in. 

Note however, that some noise should be removed before it hits the AF stage of your receiver. Some of the digital (DSP) Noise Blankers are quite impressive and then there are the Notch Filters, either the automagic ones or the manual ones (the manual dual notch filter in the IC-7000 is quite amazing).

 

There is one (two) more thing(s) I would recommend and that is using a decent speaker or two if your transceiver has two receivers. And lets not forget a good set of headphones, which will bring the recovered signal directly, without any additional noise to the HPS. 

There are of course additional measures we could apply. Like the use of a low noise receiving antenna or the use of antenna diversity.

I worked my best DX with a noisy vertical as a TX antenna and a quieter RX antenna (see above my antenna arsenal).

73 and good DX.

Footnotes:

1. The sensitivity of the receiver is dependend on the size of it ears, e.g. the RX Channel Bandwidth. The smaller that bandwidth the higher the sensitivity, the better the SNR!

HSP  = Human Signal Processor (normally found between the ears)
HIPS = Human Instructions Per Second (it has been said that a man can only do one HIPS) 

DX   = Normally used to refer to a station on another continent. From the old telegraphy  abbreviation for Distance eXchange.

SBSpectrum V.1.31 by Peter Martinez G3PLX
SpectraVue V. 3.39 by RFSPACE Inc.
SDR-IQ by RFSPACE Inc.
DXing

NOTE: This has been reposted from my old VK1HW web page and was initially written in 2018.
© ¼ ½ ¾ ⅜ ⅝ @ π ω µ Ω ε η λ °

What is your S-Meter actually displaying!

To check the S-Meter on a HF transceiver against the IARU 6 dB standard, you will need to follow a few steps:

1. Connect a known RF signal source, such as an RF signal generator, to the transceivers' antenna input.
   
2. Set the RF signal generator to output a signal at a frequency and power level that is appropriate for the transceivers' band and mode of operation.
   
3. Use an attenuator to reduce the RF signal level in 6 dB steps. You can use a set of switchable attenuators, a variable attenuator or individual attenuators to achieve this.
   
4. Connect a device that can read either power or voltage, such as a digital voltmeter (DVM), digital multimeter (DMM), power meter (PM), or cathode-ray oscilloscope (CRO), to the output of the attenuator.
   
5. Adjust the attenuator to reduce the RF signal level in 6 dB steps and record the corresponding S-Meter readings on the transceiver.
   
6. Compare the S-Meter readings to the IARU 6 dB per S-Unit/point standard to determine if the S-Meter is tracking correctly.
   
7. If necessary, adjust the S-Meter calibration on the transceiver to match the IARU standard.

It's important to note that the accuracy of the check will depend on the accuracy of the RF signal generator, attenuator and the measuring device. Which mean that to get the most accurate results it would be advisable if ones equipment had been checked against calibrated equipment.

In the past, I have used an Elecraft XG3, which I checked against a NIST calibrated LP-100A. Which in turn helped to characterise a set of switchable attenuators.

Below, you will see some photos depicting an array of attenuators and the XG3 with a step attenuator in action.

The picture on the left is showing the test setup using the Elecraft XG3 and a switchable attenuator to check S-meter tracking on my radio. As long as the test equipment has been checked against a know standard we can make fairly accurate checks using basic test equipment.

And here to the right, an assortment of attenuators.

Below is a pictorial/sketch of the current test setup I use to check the accuracy of a Radios S-meter.

Staring on the left is the signal-generator, followed by two attenuators, one in steps of 1dB and the next in steps of 10dB. The next device is a 6dB splitter which splits the signal from the signal-generator in two reduced signals. One signal going to a calibrated power-meter and the second signal to the test subject i.e. our receiver. We could replace the power-meter with a Voltmeter.

However, if the signal-generator has an accurate signal output display this can be simplified by removing the splitter and the power-meter. Using this test setup it is very easy to make sure that the check of the S-Meter is accurate. As the above picture shows, to compensate for the losses of the test setup, the signal generator is set to provide a -66 dBm signal. This is about 7 dB higher than the -73 dBm level to compensate for the additional losses, 0.7 dB from the interconnections and attenuators, and about 6.3 dB from the splitter.

Equipment used:

• Signal-generator    :HP 8656
• Attenuators         :HP-355C and HP-355D
• Splitter            :VK5HW
• Powermeter          :VK3AQZ RFPM1

NOTE: Whatever signal source or attenuator you use, make sure that its accuracy has been checked against a known reference.

The equipment I've used has been checked and aligned where necessary against NIST-certified instruments including an LP-100A RF power-meter, a Boonton RF power-meter with a 51011-4B sensor, a Fluke 8842A DMM, and a Brymen BM-869s DMM.

S-Points, are they useful

The S-Meter in an Amateur Radio Receiver/Transceiver is an indicator for the received signal strength (Strength Meter). On HF, signal strength 9 (S9) has been defined to be an input power of -73dBm @ 50Ω (dBm is power expressed as decibels relative to 1mW). This is a level of 50µV (microvolts) measured at the antenna input port. And each step between S-Units corresponds to a difference of 6dB as recommended in the IARU Technical Recommendation R.1. 6dB is equivalent to a power ratio of four and a voltage ratio of two (S-Point History).

The term S-Unit/point is used to refer to the amount of signal strength that move the S-Meter indicator from one marking to the next, i.e. it moves by one S-Point/unit. On Amateur Radio equipment, most S-Meter markings are from S1 to S9, with marking above S9 in 10dB steps.

To be able to add meaning to the S-Meter report, I believe, Amateur Radio Operators should know how the S-Meter of the radio equipment is tracking against the IARU standard. Quite a few Amateur Radio Operators either don't seem to care or don't understand the value of having an instrument that can track precise. Let's consider the below;

• Profiling a couple of antennas by listening to the background noise.  On antenna one we see a noise level of S4 (-103dBm). Switching to the second antenna we see that the S-Meter indicates S6 (-91dBm). We could now conclude that there is a noise difference between ant1 and ant2 of 12dB or that one antenna has a gain of 12dB over the other.

• Checking the front to back ratio of a Beam (Yagi/Uda) Antenna. Receiving the signal from the front of the antenna the meter reads S9. Turning the antenna 180 degree, i.e. pointing the back of the beam to the signal source, the meter reads S5. This would indicate a nice 24dB(4 S-point = 4*6dB = 24dB) front to back ratio of the Antenna, but is it true?

• Comparing receiver prowess, i.e. using a receive splitter to split the receive signal equally to compare receivers. If receiver-1 is displaying S3 on the S-Meter and receiver-2 is displaying S7 on the same signal, is receiver-2 the better receiver?

We can clearly see that if we do not know how our S-Meter is tracking, i.e. are the steps between S-Points are really equal and at the 6dB step size. We can't be sure what is being displayed. Any of the above scenarios become guess work and as such would most likely lead us astray.

 

So to come back to the question at hand, I'd say since Amateur Radio is a Technical Hobby it would be nice to provide and receive a correct S-Value report, one that is trackable to a standard. An even better report would be SNR (one for the future).

However, if one uses the Radio for NET chats and contesting, then who cares if the S-value is S9 or S9+20dB or S5 for that matter.

Would it then not be more appropriate to say the quality of your signal at my station is Q5 or Q4, i.e. going back to the old Q(SA) system. One can always ask for an S-value, but what would be the usefulness in a value that does not track to a standard.