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.

 

A Multi Frequency WSPRing (whispering) System using KA9Q-Radio

The "KA9Q Radio software suit" is a an ingenious sort of a SDR program suite. It is capable of receiving a huge number of frequencies simultaneously. I believe that this is a unique feature of this applications. It seems to go back to the original *nix philosophy of "small is beautiful" e.g. small well written applications that do one job and do this one job very well. Because there is no graphical ballast, it will perform its task on the most modest comput-hardware. Meaning it will run on a Raspberry Pi system starting with the Pi3. Note, that there is no need for an expensive GPU nor the need to use virtual audio cables or a Soundcard for that matter.

Because of the "multiple frequencies simultaneously" capability I've set up a WSPR receiver for my QTH so that during times that I do not operate I can at least monitor band activity and/or propagation. Initially I will monitor from LF (136kHz) to the end of HF (28MHz). If this is going to workout well I will also start building a system for VHF/UHF.  

Depending on the SDR one is going to use there is a requirement for a fast to really fast USB port. In my case I'm going to use the RX888M2, which needs a really fast USB3 port to stream 32 MHz of bandwidth in one go across the port. However, if I would use my Pluto or RSPdx and any of the TV-Dongles I can get away with a speedy USB2 port and for the SDR-IQ with it max 192kHz a slow USB port will do.

I can't stress this enough, the use of good usb cables is a requirement (not to long and it should have good shielding). Additionally, even though all my cables come with a molded choke, I do add additional choke(s) to all of my cables. I've had good success with that however, if that doesn't help reducing the noise from the USB/PC connection then "these" are apparently very good in suppressing CMC noise (EMI).

Below are the steps that I used to get the system up and running. And I believe that if you follow those steps you will be able to get a working "Multi Frequency WSPR receiving System" up and running in no time.

I've had a spare little PC (NUC) lying around (I7-4765) with 8GB of memory and a 250GB SSD which I bought second hand for about A$250. My installation is based on Debian Version 11.7 (Bullseye) and all following steps are based on this OS. The reason to use the NUC was to have both the SDR and the WSPR decoder running on a single host. The WSPR decoder is chewing up all the available CPU resources. 

If you go with the Pi solution I recommend at least a Pi4-4GB and to install Debian Bullseye.

WARNING: If you are going to use a Raspberry PI as the compute resource make absolutely sure that you have enough current available to support the Pi and the RX888! I use a home made 5V 10A Power-supply which is feed of the shacks 12V rail. I've tried with a powered USB-HUB to no avail!

INFO: I have highlighted text in bold, this is so one can copy and then paste the copied text into a terminal instead of typing everything into the terminal. Don't forget to press <Enter> at the end. Command returns are displayed in courier.

NOTE: sudo didn't work for me out of the box.

There are many ways to fix this issue however, I did it this way:

$ su -

#  echo "$(who am i | awk '{print $1}') ALL=(ALL) NOPASSWD: ALL" > /etc/sudoers.d/$(who am i | awk '{print $1}')

# chmod 440 /etc/sudoers.d/$(who am i | awk '{print $1}')

# ls /etc/sudoers.d/$(who am i | awk '{print $1}')

 -r--r----- 1 root root 27 May 28 20:21 /etc/sudoers.d/<your username>

So with that out of the way we can now get and install required libraries.

$ echo "

build-essential

libusb-1.0-0-dev

libusb-dev

libncurses5-dev

libfftw3-dev

libbsd-dev

libhackrf-dev

libopus-dev

libairspy-dev

libairspyhf-dev

librtlsdr-dev

libiniparser-dev

libavahi-client-dev

portaudio19-dev

libopus-dev" > /tmp/required

$ for _required in $(cat /tmp/required); do sudo apt install $_required -y; done

If you like to run the system for a while it helps if the stupid hibernation is switched off.

 $ sudo systemctl mask sleep.target suspend.target hibernate.target hybrid-sleep.target

I find it much easier to work with names rather then with ip-addresses and port-numbers, as such I'd use the Multicast DNS function of the AVAHI Daemon. Your mileage may vary though! 

$ sudo systemctl start avahi-daemon.service

$ sudo systemctl status avahi-daemon.service

 avahi-daemon.service - Avahi mDNS/DNS-SD Stack

     Loaded: loaded (/lib/systemd/system/avahi-daemon.service; enabled; vendor preset: enabled)

     Active: active (running) since Sun 2023-06-11 22:16:53 ACST; 3 days ago

TriggeredBy: ● avahi-daemon.socket

   Main PID: 548 (avahi-daemon)

     Status: "avahi-daemon 0.8 starting up."

      Tasks: 2 (limit: 9342)

     Memory: 1.3M

        CPU: 15.899s

     CGroup: /system.slice/avahi-daemon.service

             ├─548 avahi-daemon: running [sun.local]

             └─566 avahi-daemon: chroot helper

Not needed in the use case.

Check if en_US.UTF-8 language is installed.
First check:

$ locale -a

C

C.UTF-8

en_AU.utf8

POSIX

And if it is missing, run:

$ sudo dpkg-reconfigure locales

This will bring up a graphical-ui (ncurses) selection display. Scroll down until you see en_US_UTF-8, press spacebar to select and then <ok>

Generating locales (this might take a while...)

  en_AU.UTF-8... done

  en_US.UTF-8... done

Generation complete. 

 

$ locale -a

C

C.UTF-8

en_AU.utf8

en_US.utf8 <-- required

POSIX

Now download the source files for the KA9Q radio suit:

$ mkdir tmp

$ cd tmp

$ wget https://github.com/ka9q/ka9q-radio/archive/refs/heads/main.zip

Extract the downloaded file (main.zip):

$ unzip main.zip

$ ls -l

total 2.4M

drwxr-xr-x 4 hw hw 4.0K May 28 16:15 ka9q-radio-main

-rw-r--r-- 1 hw hw 2.4M May 28 18:16 main.zip

Compile and install KA9Q-Radio applications:

$ export LANG=en_US.UTF-8

$ cd ka9q-radio-main

NOTE: There are two (2) Makefiles, Makefile.linux and Makefile.pi. If you use a RaPi you need to link Makefile.pi to Makefile 

$ ln -s Makefile.linux Makefile 

$ sudo make install

Next we create a "wisdom" file. 

NOTE: Depending on your system this can take a while. Creating a wisdom file on a RaPi took a while. I cooked a meal, ate the meal, check the RaPi .... not yet .... went and watch a movie ... check again and voila done! So be patience grasshopper.

$ fftwf-wisdom -v -T 1 -o /tmp/wisdom rof500000 cof36480 cob1920 cob1200 cob960 cob800 cob600 cob480 cob320 cob300 cob200 cob160

Or if you are keen and like to know how long it took to create your wisdom file you could run the below.

$ time fftwf-wisdom -v -T 1 -o /tmp/wisdom rof500000 cof36480 cob1920 cob1200 cob960 cob800 cob600 cob480 cob320 cob300 cob200 cob160

fftw-wisdom: system-wisdom import failed

Planning transform: cob160

Planning transform: cob200

Planning transform: cob300

Planning transform: cob320

Planning transform: cob480

Planning transform: cob600

Planning transform: cob800

Planning transform: cob960

Planning transform: cob1200

Planning transform: cob1920

Planning transform: cof36480

Planning transform: rof500000

real    4m14.131s

user    4m8.088s

sys     0m0.048s

Move the generated wisdom file in to its rightful place.

$ test -s /var/lib/ka9q-radio/wisdom && sudo mv /var/lib/ka9q-radio/wisdom /var/lib/ka9q-radio/wisdom.old

$ sudo mv /tmp/wisdom /var/lib/ka9q-radio/wisdom

$ sudo chown $(who am i | awk '{print $1}').radio /var/lib/ka9q-radio/wisdom

Now its time to install the K1JT's WSPR Application.

$ sudo apt install wsjtx -y

After that is finished it's time ....  to configure/setup KA9Q-Radio for our intended purpose.

There are lots of config files and to work through all off them you'll want/need to read the documentation from here however, since I'm going to use the RX888 to do WSPR only as such I've created a new rx888.conf config file. The # and ; a comment markers. You can either modify this file with a text editor like vi or nano.

Before you copy and paste the next configuration item (below, you need to establish what the active network interface is being named! In the rx888.conf file we has a statement starting with iface. This value is system dependent and you need to find that name before you can progress any further.

On a RaPi it is most likely eth0, but on other systems it could be something else. E.g. on my system it is eno1. 

You'll be able to check using the following:

$ ip a | grep "mtu 1500" | grep UP | awk '{print $2}'

eno1: <- This is what the NIC is called on my system

Whatever the above command output shows, you'll might need to change the iface value in the below script. E.g. if it shows eth0 your iface line should read iface = eth0.

The below will create a backup of the /etc/radio/rx888d.conf file first, before creating a new /etc/radio/rx888d.conf file. 

$ sudo mv /etc/radio/rx888d.conf /etc/radio/rx888d.conf.bck

$ sudo cat << __EOF__ > /etc/radio/rx888d.conf

[rx888-loop]

# VK5HW customized

description = "RX888 40m Delta-Loop"

firmware = SDDC_FX3.img

samprate = 64800000    ;  2^8 * 3^4 * 5^5

iface = eth0               ; replace this with your iface name

status = rx888-status.local

data = rx888-pcm.local

ssrc = 10

;gain = 1.5 ; dB

gain = 10 ;dB - close to the Noise Floor, might have to increase

gainmode = high ; higher gain range

__EOF__

Next we need to configure the virtual receivers. These we do with the radiod@wspr.conf file. 

$ sudo mv /etc/radio/radiod@wspr.conf /etc/radio/radiod@wspr.conf.old

$ sudo cat << __EOF__ > /etc/radio/radiod@wspr.conf

[global]

overlap = 5

blocktime = 20

input = rx888-status.local

samprate = 12000

mode = usb

status = hf.local

fft-threads = 2

[WSPR]

# Bottom of 200 Hz WSPR segments on each band. Center is 1500 Hz higher

# sample rate must be 12 kHz as required by wsprd

data = wspr-pcm.local

freq = "136k000 474k200 1m836600 3m568600 5m287200 7m038600 10m138700 14m095600 18m104600 21m094600 24m924600 28m124600"

__EOF__

That's it folks, we are ready to start KA9Q-Radio! Make sure the RX888 is plug into the correct USB Port and then to be sure to be sure REBOOT the system.

$ sudo reboot

After the reboot, login to the system and start the rx888d(river) using the rx888-loop configuration.

$ /usr/local/sbin/rx888d rx888-loop &

NOTE: The & indicates that we would like the program (job) to run in the background.

If everything is OK the following output can be seen:

$ Using config file /etc/radio/rx888d.conf

Loading firmware file /usr/local/share/ka9q-radio//SDDC_FX3.img

Firmware already loaded

USB speed: 4

Successfully claimed interface

Samprate 64,800,000, Gain 10.0 dB, Attenuation 0.0 dB, Dithering 0, Randomizer 0, USB Queue depth 16, USB Request size 8 * pktsize 16384 = 131,072 bytes

service 'RX888 40m Delta-Loop._ka9q-ctl._udp' -> rx888-status.local (239.132.105.12) established

service 'RX888 40m Delta-Loop._rtp._udp' -> rx888-pcm.local (239.10.102.92) established

RX888 40m Delta-Loop: iface eno1; status -> 239.132.105.12:5006, data -> 239.10.102.92:5004 (TTL 0, TOS 48, 24576 samples/packet)

If this all looks ok the PC is talking to the SDR and it is time to start the demodulators.

$ /usr/local/sbin/radiod /etc/radio/radiod@wspr.conf &

$ KA9Q Multichannel SDR

Copyright 2018-2022 by Phil Karn, KA9Q; may be used under the terms of the GNU General Public License

Loading config file /etc/radio/radiod@wspr.conf...

Acquired front end control stream rx888-status.local (239.132.105.12)

Acquired front end data stream 239.10.102.92:5004 (239.10.102.92)

Front end sample rate 64,800,000 Hz, real; block time 20.0 ms, 50.0 Hz

fftwf_import_system_wisdom() failed

fftwf_import_wisdom_from_filename(/var/lib/ka9q-radio/wisdom) succeeded

service 'wspr._ka9q-ctl._udp' -> hf.local (239.83.95.156) established

Processing [wspr]

service 'wspr._rtp._udp' -> wspr-pcm.local (239.72.24.12) established

12 demodulators started

12 total demodulators started

Next start start the wspr-decoder:

$ wspr-decoded wspr-pcm.local

And voila we are starting to see decodes:

$ <DecodeFinished>

<DecodeFinished>

<DecodeFinished>

<DecodeFinished>

<DecodeFinished>

<DecodeFinished>

1518 -19  0.7   0.475683  0  VK6LX OF88 30

<DecodeFinished>

<DecodeFinished>

<DecodeFinished>

1518 -17  0.3   7.040113  0  RU0LL PN53 33

<DecodeFinished>

1518 -27  0.4  14.096975  0  WS5L EM13 37

1518 -12  0.2  14.096984  0  WB7AJP CN87 33

1518 -23  0.3  14.097017  0  <KR6RG> DM13EM 23

<DecodeFinished>

<DecodeFinished>

Looking at our home directory we can see that we have a few new directories. These are the directories of the individual virtual receivers where all the WSPR files go.

$ ls -l

total 104K

drwxr-xr-x 2 hw hw 4.0K May 29 00:54 10138700

drwxr-xr-x 2 hw hw 4.0K May 29 00:54 136000

drwxr-xr-x 2 hw hw 4.0K May 29 00:54 14095600

drwxr-xr-x 2 hw hw 4.0K May 29 00:54 18104600

drwxr-xr-x 2 hw hw 4.0K May 29 00:54 1836600

drwxr-xr-x 2 hw hw 4.0K May 29 00:54 21094600

drwxr-xr-x 2 hw hw 4.0K May 29 00:54 24924600

drwxr-xr-x 2 hw hw 4.0K May 29 00:54 28124600

drwxr-xr-x 2 hw hw 4.0K May 29 00:54 3568600

drwxr-xr-x 2 hw hw 4.0K May 29 00:54 474200

drwxr-xr-x 2 hw hw 4.0K May 29 00:54 5287200

drwxr-xr-x 2 hw hw 4.0K May 29 00:54 7038600

Lets have a look what's inside these directories:

$ ls -l 5287200

total 8.7M

-rwxr-xr-x 1 hw hw 2.1M May 28 00:01 230527_1430.wav

-rwxr-xr-x 1 hw hw 1.9M May 28 01:17 230527_1546.wav

-rwxr-xr-x 1 hw hw 1.4M May 28 09:05 230527_2334.wav

-rwxr-xr-x 1 hw hw 2.6M May 29 00:47 230528_1516.wav

-rwxr-xr-x 1 hw hw 2.1M May 29 00:57 230528_1526.wav

-rw-r--r-- 1 hw hw    0 May 28 00:33 ALL_WSPR.TXT

-rw-r--r-- 1 hw hw    0 May 29 00:55 hashtable.txt

-rw-r--r-- 1 hw hw    0 May 29 00:55 wspr_spots.txt

-rw-r--r-- 1 hw hw  452 May 29 00:55 wspr_timer.out

-rw-r--r-- 1 hw hw 2.0K May 29 00:55 wspr_wisdom.dat

$ ls -l 14095600

total 8.8M

-rwxr-xr-x 1 hw hw 2.1M May 28 00:01 230527_1430.wav

-rwxr-xr-x 1 hw hw 1.9M May 28 01:17 230527_1546.wav

-rwxr-xr-x 1 hw hw 1.4M May 28 09:05 230527_2334.wav

-rwxr-xr-x 1 hw hw 2.6M May 29 00:47 230528_1516.wav

-rwxr-xr-x 1 hw hw 2.1M May 29 00:59 230528_1528.wav

-rw-r--r-- 1 hw hw  36K May 28 23:34 all_wspr.bck

-rw-r--r-- 1 hw hw 3.0K May 29 00:57 ALL_WSPR.TXT

-rw-r--r-- 1 hw hw 3.6K May 29 00:57 hashtable.txt

-rw-r--r-- 1 hw hw  45K May 28 23:34 upload.log

-rw-r--r-- 1 hw hw   74 May 29 00:57 wspr_spots.txt

-rw-r--r-- 1 hw hw  452 May 29 00:57 wspr_timer.out

-rw-r--r-- 1 hw hw 2.0K May 29 00:57 wspr_wisdom.dat

In the 14095600 directory we find two additional files, all_wspr.bck and upload.log. These are files that my upload script is producing. The .bck file is an archive of ALL_WSPR.TXT and the .log file is for error checking.

And here is a snapshot view of a decoded dataset:

$ cat 14095600/ALL_WSPR.TXT

230528 1508 -18 -0.91  14.0969794  DP0POL JQ26 37          0  0.12  3  1    0  0  34    33  -120

230528 1508 -15  0.19  14.0969838  WB7AJP CN87 33          1  0.28  1  1    0  0  39    20    16

As it stands you now have a MULTI BAND WSPR DECODING SYSTEM. 

And now to upload the results to WSPRNet, that is also quite easy. It is  done with a one-liner:

$ curl -F allmept=@ALL_WSPR.TXT  -F call=<your call>  -F grid=<your grid>  http://wsprnet.org/meptspots.php

There is a very similar site, PSKREPORTER which not only has a database for WSPR but for a lot of other digital modes. However, I've not (yet) found a way how to upload my results to that repository.

I have automated this on my system using the *nix cron facility. I first created a script to archive the reports and create a log file for error checking. If you like to use the script, it can be found here. 

And here is my crontab: (copy the below to your crontab)

1,7,13,19,25,31,37,43,49,55 * * * * ~/scripts/upload_wspr_data.sh VK5HW PF94hk

It basically runs every 6 minutes, a minute after or before a WSPR decode.

Oh, and if you like to see if I received you go to WSPR rocks, which is an excellent tool for mapping, charting and other visualisation. 

So that's basically it. 

PLEASE NOTE, that this is NOT a how to use KA9Q-Radio, rather a quick way to show how easy it is to setup a multiple frequency WSPR receiving system using parts of the KA9Q-Radio suite. 

There are other modes that can be setup and monitored,  if you like to use other modes or even would like to manually tune through the bands and listen you'd need either a sound card or understand how to use "MULTICAST" streaming. The options are not quite endless but ...

Next on the list, get some horizontal antenna for a 2m/70cm/23cm installed and setup a WSPR VHF/UHF receive system. 

Oh and a little bragging ...

Appendix:

https://github.com/ka9q/ka9q-radio/blob/main/INSTALL.txt

https://github.com/ka9q/ka9q-radio

https://github.com/ka9q/ka9q-radio/issues

https://www.sdrutah.org/info/using_ka9q_radio.html

http://wspr.rocks/

https://www.wsprnet.org/

https://sites.google.com/view/vk1hw/antennas/vhf/2m-horizontal-phased-dipole

Why I chose to use an Audio Processor

I have been asked several times why I have chosen an external microphone processor. So, I thought it was time to put my reasons down on paper.

Some new amateur radio transceivers come with a reasonably good microphone and sound quite good when set up correctly. However, I'm not a hand-mic type of guy, and I'm also not a desktop kind of guy. When using a desktop mic, I either end up needing to go to the physio more often to get the knots out of my neck or it ends up becoming a "hand-mic".

Throughout my pursuit for a well-balanced SSB transmit audio, I have learned a little bit about audio bandwidth and how to squeeze my dulcet tones into less than a 3.3kHz audio bandwidth.

But I digress. To answer the question, I went with a dynamic studio microphone, and for that, I needed outbound amplification to drive the microphone. I also wanted/needed a bit of equalizing and compression to the audio signal. Additionally, I wanted to restrict some of the background noise that we all seem to endure at odd occasions. Therefore, my requirements became the following:

1. It needed amplification.
2. I also wanted rudimentary filtering (EQ).
3. It needed noise gating.
4. It required compression that is smooth.
5. It should fit my hobby purse.

With my wishlist sorted, I looked at what was available at a reasonable price. There are a lot of processors available, but most of them break my hobby purse. However, I finally found that the dbx286s ticked all my requirements, including requirement #5, the cost.

Here is a quick rundown of how the dbx286s fulfills my requirements:

1. Amplification: The pre-amplifier gain control runs from 0dB to 60dB, has 48V PHANTOM POWER if a condenser microphone is being used, and an 80Hz High Pass Filter (rumble filter) to take care of any rumbling at low frequencies. This is a very steep 18dB/octave high-pass filter. This filter will also, to some extent, reduce the proximity effect one gets with directional microphones.

 

2. Filtering: The dbx286s has a two-stage enhancer, the LF DETAIL and the HF DETAIL. Most enhancers work by adding a controlled amount of distortion to the audio signal. However, the dbx286s functions like an equalizer. One interesting aspect is that the LF DETAIL control applies a boost at 80Hz and a cut at 250Hz simultaneously. Many of us are aware that boosting low frequencies will often make the sound quite muddy. However, this "muddiness" is usually due to boosting frequencies other than those that would subjectively add bottom end to the signal.

You might be wondering why the 80Hz boost frequency is the same as the frequency to cut in the mic preamp stage. Well, the preamp comes before the compressor, and by removing the 80Hz before the compressor, we eliminate the compressor acting on the low (rumble) of the audio signal. This is quite different from the way AR transceivers are using MIC-GAIN and COMPRESSION.

3.Expander/Gate: Gating the audio signal to reduce background noise is a bit of an art form, and it took me quite a while to get it right. On the 286, there are two adjustments we can apply: THRESHOLD and RATIO. The ratio is adjustable up to a level of 10:1, and the threshold is variable from OFF to +15dBu. This allows me to reduce low-level clutter in the audio signal, such as breaths, without affecting the vocal itself. It's important to remember that compression raises the noise floor of the audio signal. The expander has two LEDs, one red (-) and one green (+), indicating when the audio signal is below or above the threshold. However, I found setting the gate was easier by listening to my transmitted signal on a second receiver.

4.Compressor: The compressor has two adjustments: DRIVE and DENSITY. The compression is of the over-easy type, which means the ratio increases as the audio level gets higher. This means that the Drive control controls the degree of compression. With just these two controls, I can get a very smooth compression and apply it carefully to avoid sounding over-compressed. Additionally, the 8-stage LED bar-graph shows the amount of gain reduction occurring during compression. This is quite different from the compression used in AR transceivers.

5.Cost: Yes, I achieved this requirement. The microphone and microphone processor, at the time of purchase, set me back slightly over $0.6K.

 

Here you find my current Audio Processor setup and configuration, 

and here is a very good description of all of the above.

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.