Coax Trap dipole for 12m/17m/30m/40m/80m — 30 April 2021

Coax Trap dipole for 12m/17m/30m/40m/80m

This story should begin with “when I was young” 🙂

Well, about 20 years ago, when I lived in a building with a small roof and I couldn’t install log wire antennas, I decided to build a coax trap dipole for HF bands, based on a project reported in a well known italiank book named “Costruiamo le Antenne Filari” (let’s build wire antenna) by Nerio Neri I4NE and Rinaldo Briatta I1UW.

I was attending high school and I was at the firs experience with my hamradio activity, so I didn’t have a grid dip meter, which was highly reccomended also by the authors to verfy the exact trap resonance.

I wanted to build this antenna anyway, so I tried to replicate exactly the project respecting every measure with millimetric precision, with the hope to do only little adjustment on the dipole arms lenght. But everyone who have worked with RF, knows that in practice it’s very difficult to do a trap dipole with a SWR meter only!

I built the antenna using 2,5mmq electric cable, a 1:1 balun, and built the traps using 40mm diameter plastic pipes for hydraulic systems and RG58 cable.

The coax traps were assembled in the classic configuration of the picture below:

The construction details of the trap were not published for copyright reasons.

Since the plastic pipe was not too strong, I decided to insert a small piece of 16mm pvc pipe inside the trap, and to fix the dipole to this pipe, avoiding the stress or break of the trap (see pictures later in the article).

I installed the dipole on top of a 10m pole and kept 120 degrees as arms aperture. As usual, with trap dipole the tuning should start from the higher band, which corresponds to the lenght between the traps closest to the feeding point, and then go on to the lower bands. I spent a lot of time searching for the first resonance, without any success. With much disappointment, I uninstalled the dipole and left it in a bag in my garage.

When I moved to my actual home, I went in the old garage and… I saw this old project and I remembered how much time I spent trying to let it work! But in the meantime I gained theoretical and practical experience. I don’t have a grid dip meter, but I have a NanoVNA, sto…I decided to begin another battle with this dipole!

I mad some serarch on the internet and I decided to try the following setup for searching the trap resonance frequency:

The coax trap act as parallel resonance circuit, so it looks like an open circuit at resonance frequency, while its impedance decreases at other frequencies. If the VNA channel is loaded on a 50 Ohm load and the trap is connected in parallel to this load, the return loss should show a minimum (optimal) at resonance frequency.

I did the setup as reported in the figure, with SMA to BNC transition, a BNC “T” connector and a BNC 50Ohm load. I soldered the trap terminal to a BNC male connector, and I put this connector to the free terminal of the “T” connector.

I measured all the trap resonance and I immediately understood why the dipole was not working. The 24MHz trap was resonating at about 28MHz!! All the other traps where resonating quite near the expected frequencies, but the 24MHz was completely wrong.

After different tests, I came to the conclusion that I misunderstood (or it was not clear in the book) how to wrap the trap. The plastic pipe lenght is actually too long compared to the coil, if it’s wrapped with no spacing between the turns. So I gradually started to add space between the turns and the resonance started to decrease rapidly. At the end, I reached 24MHz with all the turns spaced to the entire plastic tube, as shown below.

Then I slightly tuned all the other traps, adding some more spacing between turns and fixing the trap with plastic tape at the end. For the 24MHz trap, I decided to add some bi-component epossidic glue for fixing the turns, because the spacing was critical.

I was happy and almost sure to have found the reason the missing resonance when I was a pretty new OM, so I installed the new dipole and started to analize it with my VNA.

As soon as I did the first scan 0-30MHz with my VNA, I saw the first resonance at 24MHz! I just shortened some cm every arm, because I added some centimeters (it’s easy to cut, but not so easy to add lenght…). I was very happy for this first comfroting result which I never had during first experiments, and this told me that I was on the right way because the traps were really “isolating” the arms after the traps themselves.

Although I respected the lenght declared on my book, the resonance at 18MHz was too high, so I had to extend the wires between the 1st and the 2nd trap in order to move the resonance in the range 18.098-18.118MHz.

I had to spend a lot of time an patience to tune and optimize all the resonances, but at the end, I got good VSWR an all the bands except 40meters, on which I never get less than 1.8:1 . I tried to slightly change the spacing between the turns of the trap, but I never got values better than 1.8:1.

Here below, I attach all the measurements done with my NanoVNA on all the design bands.

In the center of the grpahs, there is a windows which shows the results of the bandwidth analysis.

Another behaviour that can be observed, is that the bandwidth drops with frequency. This probabily happens because at lower bands, the RF pass through more traps, and the “Q” factor of the traps affects the dipole bandwidth.

Here below, some picture attached.

In the picture below, I reported the original project lenghts and my experimental lenghts written by hand.

I also write some conclusions here below:

  • A 1:1 balun is always advisable. I used a commercial ferrite balun.
  • The project is quite “time-consuming” and need a lot of patience for the tuning. If you have not enough time and you need something “plug&play”, you should be better to buy a commercial trap dipole.
  • Considering the previuous point, I understand why the multiband trap dipole are quite expensive compared to the material costs 🙂
  • Always leave more wire length than the project. I suggest 30cm minimum. It’s easy to cut but difficult to add wire (I had to solder the wire and cover the soldering joint with heat-shrink tube)
  • During the tuning, always care about the simmetry between the lenght of the two arms
  • Last but not the least: the resonance of the traps shall be verified in lab before dipole installation!

73’s

Alfredo IZ7BOJ

Building the Lightweight V/U Yagi kit by Tino’S Funkshop — 24 January 2021

Building the Lightweight V/U Yagi kit by Tino’S Funkshop

I wanted to build a lightweight yagi for portable operation with my SATNOGS Az/El rotator. I surfed on the web and I found the reference site for yagi builders: DK7ZB. In the 2m/70cm-Yagis ultralight session, I found a lot of pictures of very interesting home-made yagis. I discovered that some pieces like central dipole insulator and elements supports are available on Tino’s Funkshop online store (former NUXOCOM.de) and I also discovered that, besides single yagi parts, also complete antenna kits are available.

The material for lightweight yagis is very common, so I tried to compare the price of the Tino’s Kit for 2m/70cm 13 elements Lightweight Yagi kit with the price of the same parts available on my local or online shops. I made a Bill of Material in excel with prices and… the Kit wins! Moreover, I would spent much less time for collecting all the parts and I would have the custom central dipole insulator, which is the most difficult part in my opinion.

I ordered the kit for only 21,49€ (!), payed with PayPal and I got it in a week . The shipment expenses outside Germany are about 15€ and the courier is DHL. In case of small purchases, the shipment is not negligible. Anyway, The packaging was perfect and tha materials inside were unharmed. The kit content is shown below:

The kit is composed by the following parts:

  • PVC tubes for Boom, 20mm diameter
  • 20mm PVC Clips, for elements support
  • 3,2mm aluminum rods, for all elements except radiator
  • 4mm aliminum rod, for radiator element
  • 7.5 x 4.5 x 4 cm PVC box, for feeding point
  • N panel connector
  • Small piece of 16mm PVC tube for RF choke
  • Small Piece of RG188 cable for RF choke
  • 2 metal lugs to be soldered to RG188
  • brass terminal strip with screws, 4mm inner diameter
  • All needed screws
  • Detailed instructions and datasheet

I’m going to describe main steps for building the antenna

  1. Cut all the elements to the lenght indicated on the datasheet. Be precise at mm! After the cut, remove the aluminum burrs using a flat lime.

Since the VHF reflector is longer than 1meter and the aluminum rods are 1m long, it’s necessary to lengthen it with one rest of piece from other reflectors and using the mammut connector, as the image below:

2. Drill holes in the PVC clips using 3,2mm tip. You can also try to use a 3mm tip and enlarge the hole moving slighthly the drill back and forth. In any case, you can use some glue if the element will not stay in its position. I used a stand for the drill, in order to to perpendicular holes. Anyway, don’t care if you don’t have a stand and the holes are not perfectly parallel to the clip edge, you can do small rotation once the clip is mounted on the boom.

3. Let’s insert the elements in the clamps and mark the element name in order to make the positioning easier.

4. Now, let’s proceed to the most particular part, the feeding point of the dipole.

First of all, the central hole of the insulator shall be enlarged with a 4mm tip:

Then, 2 holes of 4mm diameter shall be made on the sides of the PVC box. The caliper helped me for calculating the exact position. The, the two half dipoles can be pushed inside the insulator, passing through the box walls:

4. Now, two holes of 2,5mm diameter shall be made in the aluminum, using the insulator as guide. Don’t push too much the drill, otherwise the insulator will be ruined!

Now, the two metal lugs can be fixed on the dipole halves by two 2,9x9mm screws:

5. Now le’ts install the N socket connector to the other short side of the box. The connector has two flat notches in the threaded part in order to avoid rotations, so I suggest to drill a 11mm hole first, than work with patience and files (flat and round) as long as the connector fits inside the hole.

6. Now it’s the time to build the RF choke. Let’s drill two 3mm holes in the 16mm PVC tube and do at least 5 windings of coax cable. In my case, I did 6 windings.

Now we have to solder the coax on the dipole lugs and to the N connector. Be patient, because there is not too space inside the box. Nose pliers help in this case. Keep the unshielded part of the cable as short as possible. No matter which conductor you solder on left and right side.

7. Now let’s mark the position of the elements on the boom

This is the final result. The antenna is laying on the table of my Lunchroom. Not too bad 🙂

Since the antenna has an insulating boom, also the supporting tube should be not conductive. I had a 40mm PVC pipe in my garage, so I built this simple 90 degrees support using a small piece of plexiglass, a couple of clips for 20mm tube and a couple of clips for 40mm tube:

Then I started the first tests of my antenna. I put the antenna in my garage (it would be better to work in open space..):

Then I started my measurements with NANOVNA V2 and nanovna-saver software installed on my PC:

The first check, using default design dimensions, showed this situation for 2m and 70cm:

As you can see, it’s not too worth for the beginning, so it means that I did a good job.

For both bands, I placed three markers: red at the beginning of ham band, green at center and blue at the end. The span is greater than the usable bandwidth in order to have a better understanding of the antenna behaviour.

As suggested on the manual, I started to tune the VHF resonance, so I started to cut 2 or 3 mm at time on both ends of VHF radiator. The resonance vary quickly with the lenghts, so be patient and don’t exceed with the cut lenghts!

At the end of the tuning, I got 980mm. The starting design lenghts was 995, so I cut 15mm. The resonance is shown below. It’s not perfectly centered at 145, but the SWR is <1:1.3 across the whole 2m band, so it’s ok for me:

As suggested by Nuxocom, I started to move the Open Sleeve radiator of 70cm for UHF tuning. The open sleeve is the passive element which is very near to the 2m radiator, and it’s a passively coupled radiator excited by the 2m radiator. I didn’t lower the resonance as much as I wanted in this way, so I started to cut the open sleeve (it’s allowed by nuxocom). At the end of tuning, the open sleeve was 320mm. The desing length was 329mm. The final situation is shown below:

The VSWR response is very flat and it’s <1.3:1 anyway. Good!

Now I’m waiting for real tests/comparison in open air, but i have to wait for better weather condition to go on my roof.

Concluding, the kit is highly suggested for OMs that have a minimum of manual skills and like to build antennas, but at the same time don’t have too much time for collecting material and want to start from a well tested configuration in order to have guarantee of success!

The kit is very complete and nothing else is necessary to build the antenna. The quality of the materials is very high and the price is very cheap compared to local shops.

Building instrunctions are also very detailed and easy to understand.

Everyone can customize the antenna and follow different solutions, but the suggestions, in my opinion, are the best way for good and quick results.

The only modification that I would consider, is to replace the steel screw and nut at the center of the dipole insulator (not visible in the previous pictures) with a nylon equivalent, since the screw is very near to the radiator parts (the center gap is only 10mm).

I didn’t have a 4mm nylon screw during the assembly, otherwise I would have changed it.

I hope this could help next OMs that want to build a twinband yagi and would consider a kit.

73′

Alfredo IZ7BOJ.

Refurbishment of an old TONNA F9FT Antenna — 9 January 2021

Refurbishment of an old TONNA F9FT Antenna

In the early 2000’s I bought an F9FT 21 elements antenna. I used it during the golden age of packet radio and I enjoyed the beautiful performances of this yagi for establishing links across long distances. The datasheet and manual can be found here below.

When I moved out of my city for work, I uninstalled the antenna from the roof and I stored it without any maintenance. Recently, I needed this antenna for experimenting a link with New Packet Radio. I recovered the antenna from my garage and I found it in very bad conditions. Consider that the antenna was installed very near to the coast, so the sea salt increased the corrosion.

As you can see, the aluminum parts were full of oxide and the feeding point of the folded dipole was completely broken. I didn’t use more than 25Watts, so I think the plastic was broken due to atmospheric and thermal stress. The inox screws are still perfect, but the clamps are rusty.

I have been tempted to buy a new antenna, but the OM should be patient, should save money and love repairing so… let’s repair!

I started from the more boring job: cleaning the aluminum parts. I decided to avoid acids and use only WD-40 and an inox sponge.

It took about 2 hours but the results are good.

Then, I cleaned all the isolators with a brush and Chanteclair. I also cleaned the inox screws with WD-40:

Now it’s the turn of clamps. I used the circular metallic brush mounted on the drill, and a bench vise to hold the pieces during the operations and work in safety. Here below the pieces before the cleaning

And after the cure:

The final step is the painting with spray Zinc. I used the following, a good quality one:

The clamps looks like new after painting. I preferred to pur 2 coats of paint for a better results.

The last but very important operation is the restoration of the feeding point. I found the complete and original TONNA dipole as replacement part, but it’s not very cheap (about 30$ + shipment expenses). So I decided to build it by myself. I decided to use an ABS 10cmx10cm electric box, an SO-239 flange connector (I didn’t have N type in my drawers, but it would have been better…) and two brass electric terminals for contacting the aluminum elements, which are not weldable. The pictures below explains better my idea.

I installed and tested my antenna and it works perfectly. The ROS is 1.2:1 at 431 MHz. The resonance frequency is slightly shifted down compared to the design (432MHz), but the bandwidth is still good.

Here below some pictures of the installation.

73’s

Alfredo IZ7BOJ

A simple Web interface for APRX — 2 August 2019

A simple Web interface for APRX

I use Aprx from many years and I think it’s one of the most complete and flexible APRS Software available. Nevertheless, every time that a sysop wants to check his aprx node, he has to check the log and try to analyze it. Even simple operations, like check if a certain callsign has been heard by the node, could be cumbersome.

In case of monitoring or troubleshooting, I usually download the log file and then import it in excel and then analyze it by filters and other useful functions.

Before Aprx, I used for many years the aprsd daemon, and it implemented a simple but very useful web interface with simple reports. While I was remembering that interface, I thought that a web interface could be useful for aprx too, and I started to google for this kind of software, hoping to find a plug&play solution.
I was very surprised to find something. I tried just a pair of interfaces, then I choosed “aprx simple webstat“, written by Peter, SQ8VPS.

This is a simple statistics and information generator for APRX software, which allows to monitor load, frames, stations details, statistics from selected time window and more.

I quickly downloaded and installed it. I got it working after few minutes, because I already had lighttpd server installed on my raspberry, so just did a quick configurazion of the log file path and other few things.

I started to use it and I liked it very much. I contacted Peter by email, and I congrats with him for his nice work. Peter is a young OM from Poland, he still attends school but he’s very clever and has very good programming skills and know-how about aprs.
He was very surprised and happy that someone was using his interface!
We had a nice opinions exchange and he asked me for new ideas for improving the interface.

Thanks to this renewed enthusiasm, I started to propose the improvements and he started to implement my ideas and releasing new versions.
I always intend hamradio hobby like an opportunity to explore and learn new things, so I decided to take this occasion to learn php.
I already developed something in jsp, but php was a quite new language for me, and it was a challenging activity.
In the meantime, Peter became very busy with school, driving license and other things, so, in the last period, I developed some new features and bug fix by myself and Peter did the “merge” on github.
Hereafter, I breafly explain the main functions of the Software:

  • Polish and English language
  • Possibility to monitor multiple radio interfaces
  • Possibility to show cusom info and custom logo file on the bottom of the page (edit “custom.php” file, which can contain HTML and PHP code)
  • Management of SSnN “State” abbreviations aliases;
  • Counters of:
    – total frames in log
    – frames received by radio
    – frames transmitted on radio
    – frames received from APRS-IS
    – received frames/sec (calculated on last 20 frames)
    – transmitted frames/sec (calculated on last 20 frames)

aprxsw_home1
Figure 1 : homepage – first part with custom.php

 

  • System status table (reads parameters directly from OS):
    – OS version
    – kernel version
    – Aprx version
    – System uptime
    – CPU temperature
    – CPU frequency
  • Aprx config table (read parameters directlty from aprx.conf):
    – Beacon interval
    – APRS-IS server
    – Location coordinates
    – Tx active/not-active
    – Number of radio ports
    – Digipeater active/not-active

 

aprxsw_home2
Figure 2 : Home page – tables view

 

  • Heard station list table (observation period selectable by the user in a drop-down list)
    – Heard Callsign
    – N. of packets heard for callsign
    – Direct link for showing the station on aprs.fi
    – Static/moving indicator
    – Via indicator (digi/direct/digi+direct)
    – Raw packet view for each callsign

aprxsw_stationlist
Figure 3 : home page – station list view


 

  • Station details page:
    – N. of frames totally heard
    – Last position frame heard
    – Station position (lat,long, distance and bearing from your location)
    – Frame comment
    – Frame type (normal/Mic-e)
    – Station symbol
    – Frame digipeating path
    – Transmitting device (device list can be updated by dedicated file. Both new and  legacy Mic-e devices are included)
    – Last status frame heard
    – Status field

aprxsw_details
Figure 4 : station details page


 

  • RAW FRAMES page: log of raw frames received from a specific station

aprxsw_rawframes
Figure 5 : RAW packets page


 

  • Possibility to sort the table in ascending or descending order on each colum.
  • Live monitor page: ajax page for watching ax25 traffic in realtime. Fields are coloured for better readings

aprxsw_live
Figure 6 : AX25 Live traffic page


 

You can see my APRX Simple Webstat interface at work here: http://iz7boj.ampr.org/aprx.html

The github repository with SW installation instruction is here: https://github.com/sq8vps/aprx-simplewebstat

Note1: This is a BETA software. It can contain some bugs and may be written in non-efficient way. Please contact authors if you find any bug.

Note2: Project is free for non-commercial use. You can modify and publish this software, but you have to put an information about original authors.

I hope that aprx users could install and enjoy this interface.

For any further details or questions, don’t hesitate to contact me!

I would like to say thanks to my colleague Peter SQ8VPS, which thought, developed and mantained this beautiful interface.

73’s

Alfreo IZ7BOJ

Python script for Raspberry thermal control and MCP3008 ADC — 5 June 2019

Python script for Raspberry thermal control and MCP3008 ADC

When I built a telemetry system for DMR repeater, I observed high temperatures of the transmitting radio, especially during summer and hot periods of the year.
I realized that a cooling system could be helpful to dissipate the heat produced by Motorola radio.
The acquisition system was already done, so only the actuation system was needed.
I searched on the internet, and I found some scripts used to control a fan installed on the microprocessor of the raspberry Pi.
I took one python script and modified to acquire the temperature of the external sensor connected to the MCP3008.

The original script was here (reads the System CPU temperature) and the customized version is here.

Some notes for the correct script configuration:

  • Script Cycle time must be configured. Default value of 30sec is good for starting;
  • Log file name must be declared.
  • Output pin to be used for fan switch on;
  • Both upper and lower thresholds must be declared, as for every hysterical control;
  • The logging function can be useful during the first tuning period. Once the thresholds have been found, the function can be eliminated;
  • Value, beta and pull-up resistor of NTC must be declared inside the script for a correct temperature conversion. The NTC, in series with the pull-up resistor, must be connected to the the same 5V coming from the Raspberry and powering the MCP3008.

    NTCbias

  • ADC channel connected to the NTC sensor must be specified.
  • Adafruit library for MCP3008 must be installed before running the script.
  • A compensation variable is useful to align the temperature reading to a reference thermometer.

I used two small 12V PC fans, which fits well to the Motorola heatsink:

img_8634.jpg

The Raspberry output pin cannot directly drive the fan, so a small BJT driver is needed. I built one with a 2N2222 NPN transistor and a 1KOhm resistor, 1/4W on the base.
Here below the schematic is reported:

Circuit-using-2N222-NPN-transistor

This is the prototype board of the fan driver:

IMG_8631

The general block diagram is the following:

schema

Once the hardware is ready, we can try to manually switch on pin 25 and see if the fans start, using “GPIO” library from shell:

gpio mode 25 out
gpio write 25 1

The above commands set pin 25 as an output and then sets the pin to a logic 1.

If the fans starts, we can try to configure and launch the script. Remember to give the execution permission (sudo chmod +x MCP3008_raspy_thermostat.py).

In the logfile, we can read the temperature acquired by the NTC and eventually tune the “compensation” variable to align the temperature reading with a reference thermometer.

Then, we can tune the thresholds for best results.

I hope this project could be useful.
73’s
Alfredo IZ7BOJ

SPF5189Z LNA measurements on VNA — 11 April 2019

SPF5189Z LNA measurements on VNA

Since January 2019, I’m sharing a simple satellite receiving station on SATNOGS network, based on a RTL2832 USB SDR dongle and a home-made turnstile antenna.

The RTL2832 Noise Figure is not so good (on the internet I read about 7dB), so one way to increase the receiver performance is to place a LNA as near as possible to the antenna.

I searched on the internet, and I’ve found the LNA4ALL a very good  solution. It also has an internal bias tee in order to be powered directly on the coax cable.

Nevertheless, it’s not very cheap and the shipment expenses are too high, then I decided to try first a SPF1589Z LNA for few euros from ebay, then decide if throw it away or keep it.

foto

It arrived in about three weeks from China, then I wanted to test it on a Vector Network Analyzer, in order to compare the real gain with the datasheet.

Once the LNA has been powered at 5V, the current absorption is 90mA, perfectly aligned with the datasheet range.

Here below, the S21, S11 and S22 plots are reported between 50MHz and 3GHz (the LNA reaches 4GHz but the VNA not).

I palced these 4 markers:

  • 144MHz
  • 435MHz
  • 1GHz
  • 2GHz

S11
Out

S21
Gain 50MHz-3GHz

S22
Output Return Loss 50MHz-3GHz

When I downloaded the datahseet, I saw that the SPF5189Z has two possible configurazion:

  • Optimized matching at 900MHz
  • Optimized matching at 1900MHz

From ebay description and board P/N, it’s not possible to understand the frequency optimization.

Here below, I reported a comparison the datasheet (green line) and the measurement (red line) data, for both configurations. The frequency range of the datasheet is smaller than my measurements, sto the comparison is only on the datasheet frequencies and not wide-band.

900MHz_measured_vs_datasheet1900MHz_measured_vs_datasheet

The gain seems to be 1dB less than the datasheet on both configurations, while the input matching shows better results on 900MHz range.

At the end, the LNA is quite wide-band and is a compromise between the 900MHz and 1900MHz configurations.

In the next days, I will install the LNA near the antenna and I’ll let you know the improvements on the receiver.

Best 73′

Alfredo IZ7BOJ

APRS: how to automatically monitor a group of Digipeaters and I-Gate — 4 March 2019

APRS: how to automatically monitor a group of Digipeaters and I-Gate

In the early 2000’s , together with Piero I7IGX, an APRS digipeater was installed in Trani, my Town. For about an entire decade, the Digipeater IZ7BOJ-11 was almost alone in the region, but..starting from 2016, thanks to my dear friend Luigi IZ0YAY (now back in zone 7 for QRL), the interest for APRS increased again!

Luigi involved other OMs and other digipeaters were installed. A beautiful technical exchange started between the sysops, and sometime we had to announce temporary down-time of our nodes on a whatsapp group.

Most of us are very busy for QRL, so it’s not easy to constantly monitor the state of our node, then I thought to an automatic monitoring system, whit these two simple purposes:

  1. Gather information of all nodes of the group and show the situation in a simple (possibly graphical way)
  2. Sends alerts on whatsapp or telegram in case of technical problems on the nodes.

The first concern was: how it’s possible to determine the status of a Digipeater or I-gate, in terms of vitality? Well, the first idea is to use the most powerful database in order to see the “last heard” time. This is possible thanks to aprs.fi and its API, which allow the direct connection of a custumer application directly to the database.

The second concern was: given that the method to determine the vitality is the “last heard time”, which is the right timeout before declare a problem on a station? Well, this parameters has been tuned experimentally.

I then developed a simple web interface in php, and emedded a view of all apulian station in APRSdirect (I had some problem trying to enclose aprs.fi into a view).

Here below a picture with a tipical situation.

The website is hosted at http://iz7boj.dyndns.org/aprsdash/aprsdash.php

schermata-2019-03-04-alle-11.59.53.png

The main query is the following:

https://api.aprs.fi/api/get?name=.$stationsquery.&what=loc&apikey=.$apikey.&format=json

which returns, for every station declared in $stationsquery,  its basic location and other basic data, including “last heard” in JSON format (see aprs.fi api help for furher details)

The variable “$stationsquery” is declared inside the config.php file.

The output of the query is then parsed and the last time converted from Unix Time to a human readable format, then compared to the timeout.

The source of the packet (TCP-IP or RF) is also showed. This information is useful in order to understand if a compound station Digi+Igate has problem on RF side.

The sources are available at: https://github.com/IZ7BOJ/APRS_dashboard .

If you want to use the dashboard, you must have php libraries and a web server installed. Copy the content from Github to your web server folder, then edit config.php file with the following informations:

  1. stations to observe
  2. aprs.fi APIkey (you must have an account or aprs.fi)
  3. timeout (default is 30min)

Well, now we have gathered all the necessary information to a dashboard. This is helpful, but you will never now that your node has a problem, unless you open the dashboard. For this reason, I thought to an automatic systems which sends alerts to our smartphones. Telegram is the easiest choise, since is an open-source  and well documented Application.

Preferrably, the criteria for the vitality should be the same of the dashboard (last heard) and the database should be aprs.fi again.

After some researches on telegram BOTs under python, I found a very useful library to install to my raspberry for sending notification: the library is “telegram-send“.

You can install telegram-send with pip:

sudo pip3 install telegram-send

then, depending by the destination of your messages, you can choose:

  • telegram-send –configure if you want to send to your account
  • telegram-send –configure-group to send to a group
  • telegram-send –configure-channel to send to a channel

The source code can be found here:

https://github.com/IZ7BOJ/aprs_station_monitor

Note that the daemon should continuously run in background, since it stores the status of the nodes (in terms of “dead/alive”) and sends messages only when a state change is triggered (from dead to alive and viceversa).

This daemon runs and sends notifications since summer 2018 and no problems are detected.

Here below, a screenshot of some messages received on telegram is reported, for example only:

telegram_screen_aprs

Best 73’s

Alfredo IZ7BOJ

Brief history of my Packet Radio and Wi-Fi activities — 3 March 2019

Brief history of my Packet Radio and Wi-Fi activities

I’m going to describe my hamradio activities in the early 2000’s, particularly in area of packet radio, which was my preferred.

I became a member of local ARI (Associazione Radioamatori Italiani) club in 1997, when I was only 17 years old and I was attending the school (Technical Institute for electronics and telecommunication). In that period I knew Piero I7IGX,  one of the first packet radio experimenter in my zone, who managed the local packet node IR7BA. In those years, internet was weakly entering in people houses by slow telephone modems (33Kbps or 56Kpbs).

When I became familiar with packet radio, thanks to I7IGX, I helped the local ARI club to improve and add features to the packet node IR7BA, and I learned with I7IGX how to work with TCP/IP over AX25, with the famous Softwares JNOS (DOS).

A lot of TCP/IP routing experiments  were conducted together with Raffaello Di Martino (ex IW7CHV, now IZ0QWM), and his brother Raffaello (ex IW7EAS, now IW2OHX), between IR7BA and Bari Nodes.

Also and a FTP, HTTP and mail servers were activated and a simple website with basic information was developed for IR7BA.

The increasing number of users of BBS, the frequent file downloads through YAPP protocol and the curiosity for packet radio, highlighted the real bottleneck of the packet network: the speed.
IR7BA had two main access ports: VHF@1200baud and UHF@9600baud and there was no internet connection in the first period.

In 1990, Dr, Matjaz Vidmar S53MV (a true idol among packet enthusiasts) published on “CQ Elettronica” Magazine some projects for home-made Wide-Band FM Radios and Modems, capable of 38400baud packet traffic at 430MHz. They were very innovative projects: even stripline technology was used for the RF sections!

In Italy and Slovenia, a fast network called “Supervozelji” was growing thanks to these 38400baud radios. Some years later, Matjaz Vidmar published a project for 1,2Mbps radio and the Italian Backbone was consequently upgraded. The early 2000’s represented, for me, the golden age of the Italian packet radio.

Here below, a picture of me, IW7BNO, IW7DWL, IW8DDV and other Apulian packet radio enthusiast at the bottom of IR7GRA node (Gargano, Apulia):

ir7gra

I7IGX proposed to me to build a couple of radios and modems, at 435MHz and 1,2GHz. In those years, I was attending the University (Electronic Engineering) and the free time for the hobbies was very limited. I started to build the radios, although I didn’t have all the necessary theory and practice.

Thanks to the help of Lorenzo IW6OCM, the UHF radio was successfully built and tuned, together with the Manchester modem and a SCC (Serial Communication Controller) PCI card, which was necessary for an efficient serial flow control between the modem and the PC.

Here below, a picture of 70cm radio is reported:

dsc_0127.jpg

Thanks to this radio, IR7BA was successfully linked at 38400bps to IR7GRA, owned by Angelo IW7BNO, another packet-radio enthusiast who managed several packet nodes in my region.

I built another UHF radio on the same frequency of IR7BA, and I reached another important milestone:

The first audo/video-call, using Microsoft Netmeeting, was done from my house Piero I7IGX, which was connected via ethernet on IR7BA. It represented the fulfillment of an old dream.

Here below, you can find a picture of IRBA equipment. I built all the equipments in the aluminum boxes 🙂

ir7ba

Being very proud of these first results, together with Fabio IW7DWL, I finalized the 1,2GHz radio. In those years, the RF instruments were very expensive and were difficult to find for a ham use. With courtesy of one my professors, I was able to use, only for few hours, the spectrum analyzer of my Technical School, and finally me and IW7DWL got our radios working. The link was established at few Kilometers, from me to Fabio’s house, but the link was good.

Here below, a picture of 23cm WBFM radio is reported:

dsc_0120.jpg

I was very satisfied, because in those years I was studying electronics and telecommunication at university, I could do practice on the hardware! I spent a lot of time and a lot of nights soldering, building and making tests in my lab.

In the 2003/2004, IR7BA was equipped with an internet connection and became an internet-gateway.

After some years of experiments with these radios, the Wi-Fi started to spread among the ham world, and the packet network was slowly upgraded with wifi links, especially the backbone links.

In the same years, together with Piero I7IGX, Nicola IK7SMY and Mauro IW7AVY, we developed a Bi-quad antenna for 2,4GHz and we enclosed a D-Link DWL-900AP+ access point in an outdoor box with a home-made power-over-ethernet system. Another important success was reached in 2003: the first local link upgraded to Wi-Fi!

Here below, some pictures of the home-made wifi outdoor box:

For furher details of the outdoor box project, see this website (italian, developed in 2003)

In the next years, other antennas were developed, built and installed on IR7BA: a vertical collinear, and a 3D-corner reflector, for longer links.

Here below, some pictures of 3D home-made corner reflector antenna (thanks to Mauro, IW7AVY for the nice manufacturing of copper parts):

In the next years, domestic access to internet became very fast and cheap, thanks to the ADSL connection. The interest for packet radio started to decrease and I had to move to Rome for work. IR7BA continued to live until 2010, when a thunderstorm and other technical problems on the equipment arised and there were not enough users to justify the effort for the system maintenance.

I continued my experiences with hamradio TCP-IP on 5,7GHz. I experimented mesh-networks and OLSRD protocol, joining ninux group (one of th world’s most active mesh neworks group) end applying hamradio IP numbering (44.x.x.x) on the nodes.

Here below, me after succesfully installing a Wifi link between me and IZ7YDL (about 20km distance):

wifi

Nowadays, the packet radio is limited to aprs and other simple applications, but while I wrote this article I felt very nostalgic of this beautiful period of my life, when every information was not so easy so find because it was not ready on google, when it was necessary to keep in touch with other colleagues much more than today in order to increase the technical knowledge and to find solution to the technical problems, when I spent entire nights just to see packets decoded on my CRT screen and, yes..it had the taste of a fantastic conquest. yes, I know that I’m getting old 🙂

Alfredo IZ7BOJ

ESEO GNURadio decoder optimization — 7 February 2019

ESEO GNURadio decoder optimization

After the launch of ESEO, at the end of 2018, Daniel Estevez released his beautiful GNURadio decoder: https://destevez.net/2018/12/decoding-eseo/

I started to use it and tried to do some optimization.

After some hours spent in “trial and error” I’ve found this two tricks to improve the success of decoding satnogs recording files:

1) Decrease the “Multiply Const” from 1 to 0,7 (Daniel Estevez already talked about the big gain of satnogs recording)

2) Increase the cutoff frequency of Lowpass Filter from original 4,8KHz to 5,2KHz (sometimes 5,3KHz)

Moreover, Dr. Chris Bridges suggested me to add a HighPass filter with a cutoff-frequency of 50Hz.

Cattura

I tried this modifications with this satnogs observation: https://network.satnogs.org/observations/439335/ and the decoded packets increased from 235 (original configuration) to 322 .

I hope this suggestions can be useful to other people who want to use eseo decoder.

73’s

Alfredo IZ7BOJ