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, some say they have 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 (the moaning and groaning ones) are being heard (at the other end) 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 as me, 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 more then 3 kHz wide. No I'm talking about stations that are in, or just above our received noise floor. And second, I refer to Single Side Band (SSB) but, through out the following I will show the effects on a CW signal to make it easier for me to show the effects of the used counter measures.

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 with the following software SpectraVue Ver. 3.39 and SBSpectrum Ver. 1.31. And, to have a steady RX signal I'll be tuning the radio to our local NDB (RX via 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 received signal strength will be lowered. However, not only will the signal will be lower but also the received noise will be lower [1]. And, this is the aim of the game,  if we apply our tool-set 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. Most receivers have a basic RX-BW of about 3 kHz. And most Voice transmissions are with a 2.8 kHz transmit bandwidth (TX-BW) (yes yes I did say most). Now if we look at those number we can see that we already have 200 Hz of unused RX-BW and this 200Hz is filling our receiver with noise (RX-BW3000-TX-BW2800=200 Hz of noise) Imagine if the transmitted signal would have a TX-BW of 2.4 kHz and we would receive the signal with a 3 kHz RX-BW. We would now receive 600 Hz of additional noise. 

 

So to improve the quality, aka reduce the excess noise the receiver is hearing, 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 TRX's shine, they use "software" (DSP) to do the filtering and some of those DSP implementations are exceptionally good. 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 received signal.

 

And so, by adjusting our RX-BW to the TX-BW of the received stations, we would improved the SNR by 600 Hz. And contradictory to my earlier statement [1], on a good receiver with a good and accurate S-Meter, we would be able to see that the noise floor has dropped and that the signal has gone up. 

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

The grey area is the noise which we are receiving. Looking at the bottom of that grey area we can see a 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 we get the impression that the signal has become stronger i.e. it is more audible, it is clearer and more intelligible. If we widen the RX-BW again it becomes clearly visible that the signal looses  its intelligibility as its fading back into the grey (noise) again (picture below).

Reducing the RX-BW is one of the most effective ways to improve the received signal quality (SNR). Even if I receive a signal that does not limit its TX-BW to say 2.8 kHz I always run 2.4 or even 2.1 kHz RX-BW on SSB. I even go as low as 1.7 or 1.5 kHz RX-BW if the going gets tough but that has mostly to do with adjacent channel QRM. 

 

If you tune above 7.2 MHz 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/stronger.

 

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 picture below shows the AGC disabled for the first part and then, enabling the AGC the noise disappears and we can see how 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 receivers and the design (Superhet vs DDC) of a receiver. I have the ability to set three different AGC settings per mode on my TRX for different noise events/modes. I.e., I have a slightly faster AGC recovery time for thunderstorm/lightning QRN than for quite band conditions. I also have different AGC timings for different the 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, it speaks for itself. NOISE what NOISE?

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 however, 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 2.4 kHz 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 150 - 2350 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-improvement-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 i.e., 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 Blanker are quite impressive and then there are 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) additional item(s) I would recommend, which 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 environmental 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 the TX antenna and a quieter RX antenna (see above my antenna arsenal).

73 and good DX.

Footnotes:

1. The sensitivity of the receiver is dependent 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 most Amateur Radio equipment, S-Meter markings are from 1 to 9, with marking above 9 in 10dB steps.

To be able to add meaning to the S-Meter report, I believe, an Amateur Radio Operator should know how the S-Meter of his/her radio equipment is tracking against the IARU standard. 

However, 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 to a standard. Statements like "Everyone's S-Meter is correct"  meaning it is a relative only report is meaningless and as such useless. (See below for an alternative, a more "relative" report.

 

Let's consider the below;

• Profiling a couple of antennas by listening to the background noise.  On the first antenna we see a noise level of S4 (-103dBm). Switching to the second antenna we see that the S-Meter indicates a noise level of S6 (-91dBm). We could now conclude that there is a noise difference between ant1 and ant2 of 12dB ! Could that mean that one of the 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 this believable?

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

It should be clear now that without an understanding of how our S-Meter tracks, any of the above would be guess work and will give make believe results. Most of the reports one hears these days could be labeled as Snake Oil reports.

 

So to come back to the question at hand "are S-Point useful"? 

 

My take on this is  that since Amateur Radio is a Technical Hobby it would be nice to provide and receive a S-Value report which is based on a standard e.g., the IARU recommendation.

 

Now there would be an even better report, one that is based on the Signal to Noise Ratio (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.

A little history about S-Points

The evaluation of signal strength using S units in the RST system was developed in 1934 by the Radio Amateur W. Braaten, W2BSR, and adopted in 1938 by the ITU. As receivers in the past often lacked a reception level indicator (S-meter), the RST system was based on a subjective hearing assessment of the received signals. RST stands for Readability, Strength and Tone Quality. And S1 represented a barely audible signal, while S9 represented a very strong signal. 

• In 1981, the International Amateur Radio Union (IARU) assigned shortwave reception up to 30 MHz the following S-levels, starting with the upper reference value of 50 microvolts (-73dBm) for an S9 level. 
• Each S-level below is half the voltage of the previous level, with a level of 0.2 microvolts (-121dBm) assigned to an S1 level. 
• Since a voltage ratio of 1/2 (50% or 0.5) corresponds to a 6dB decrease on a logarithmic scale, the proverbial "6dB per S value" was established.

NOTE: One S-Point really equates to 6dB!

Received Voltage		Received Power (Zin = 50 Ω)	Signal Strength (S-Value)
-14.0 dBμV	0.2 μV	-121 dBm	1
-8.0 dBμV	0.4 μV	-115 dBm	2
-2.0 dBμV	0.8 μV	-109 dBm	3
4.0 dBμV	1.6 μV	-103 dBm	4
10.0 dBμV	3.2 μV	-97 dBm	5
16.0 dBμV	6.3 μV	-91 dBm	6
22.0 dBμV	12.6 μV	-85 dBm	7
28.0 dBμV	25.1 μV	-79 dBm	8
34.0 dBμV	50.1 μV	-73 dBm	9
40.0 dBμV	99.9 μV	-67 dBm	9 +6
44.0 dBμV	158.3 μV	-63 dBm	9 +10
46.0 dBμV	199.3 μV	-61 dBm	9 +12
52.0 dBμV	397.6 μV	-55 dBm	9 +18
54.0 dBμV	500.6 μV	-53 dBm	9 +20
58.0 dBμV	793.4 μV	-49 dBm	9 +24
64.0 dBμV	1.6 mV	-43 dBm	9 +30
74.0 dBμV	5.0 mV	-33 dBm	9 +40
84.0 dBμV	15.8 mV	-23 dBm	9 +50
94.0 dBμV	50.1 mV	-13 dBm	9 +60

As such the S-Meter/indicator should display the receiver input voltage divided into S levels from S1 to S9 based on 6dB per step.

Oh no, there is no S0

Yes, to the surprise of some people, there is no S0. There is no S0 because it represents the absence of a signal, which is not measurable. (Albeit lots of HAMatuers think there is)

An observed on-air signal report: "I have noise on the frequency, so your signal report is R5 by S0 to S1" this can be confusing, as S0 really means I can't hear anything. (see S-Point are they useful) 

On the other end of the scale, input voltages greater than S9 are displayed as "x dB over S9". I have found that most newer HF-Radios are tracking very good above S9 and that S9 also seems to be fairly accurate to the -73dBm/50μV.

The definition of S9 = 50μV (-73dBm) as the reference level for frequencies up to 30 MHz was based on the sensitivity of conventional receivers at the time and the atmospheric background noise typically present at shortwave (a different reference level applies above 30 MHz).

Most S-meters are not exact level indicators but simply display the AGC control voltage. The result is often no more than an estimate of the actual input voltage. However, accurate S-Meters (low-power level meters like a field-strength-meter) are quite possible by tapping the IF and using log-amps as can be seen here (page 21), and of course in software as in Software-Defined Radio (SDR).

Remember that S levels are not a physical quantity, they are but a practical tool for the simple specification of received field strength levels. 

I believe a better choice would be a meter with a scale in dBm or μV, but only if the meter tracks properly.

NOTE: Due to the lower external noise above 30 MHz, a higher receiver sensitivity is required at VHF.

For this reason, the reference level for S9 was set 10 times lower for the frequency range above 30 MHz at an input voltage of 5μV. However, the 6dB step remains the same.

Checking my transmitted radio frequency spectrum

Using an ICOM IC-7610 into an amplifier which is connected to an 800W homebuilt dry dummy-load for testing. Now I could drag one of the Spectrum Analysers up to the shack or bring all the AR-equipment downstairs (fat chance). So I decided to use my trusty old SDR-IQ. As this is not an accuracy test/measurement rather a quick check to see how the signal looks before it goes out into the ether. Using an SDR and a PC makes it easier to snap pictures of the result for later comparison.

Here is a quick view of the setup:

TRX : IC-7610

AMP : SPE

LOAD: 50Ω 800W with 40dB Tap

ATT : 20dB

RX  : SDR-IQ

PC  : Laptop with Spectraview 3.39 connected to RX via USB2

The below picture shows me what my transmitted signal looks like. Instead of using my Elecraft two-tone generator I was using my voice and by creating a rather harmonic rich sound (don't ask, the wife came running in and thought I needed attention) the below spectrum showed up on the "Spectrum Analyser".

And here is my Voice caller, calling CQ ....

And here is a spectrum display using a TX bandwidth of 2800 Hz, 100-2900.

Even running a wide audio setup the spectrum of the signal is well contained.

Here you can see how my ICOM IC-7300 fared when checking the output signal.

Here is a device you could use to monitor your transmission with a cheap SDR receiver, a CRO or a Spectrum Analyser.

And below is a spectrum plot of my signal on 20m: