My sark100 antenna analyzer

In september 2016 I ordered a balun and a linked dipole kit from sotabeams with the idea to make a lightweight dipole antenna for outdoor use. But there is one very important ingredient to making a dipole: you need an antenna analyzer to get the dimensions right to have optimal reception and transmission into a resonant antenna.

I could borrow the antenna analyzer from the club just like I did for measuring my 2m/70cm portable coax antenna but after reading about the (cheap) SARK100 antenna analyzer I decided to buy one myself. One good review I found is It finally arrived! My SARK100 from China. This analyzer seems to be a serious case of an 'open source' design being picked up by the Chinese electronics manufacturers and sold in high numbers. I bought one for a reasonable price at an aliexpress seller that had good reviews and orders before.

It arrived today and the first tests look really good. First I measured my dummy load (to get an idea of how it was doing as an analyzer) and after that the 10m/20m/40m endfed antenna that was hanging outside anyway for the EU PSK DX Contest 2017 that I participated in. This antenna isn't perfect (as visible in the picture) but it does the job.

So now I have to find the time to design a linked dipole as I want it and to go outside and make it all happen.

I noted the EU PSK DX Contest in the contestcalendar and decided to participate. Conditions did not cooperate very well and I found some issues with my setup during the contest. But in the end I made 57 contacts. Not very good given my scores earlier this year but I think the big issues with local HF noise started after the previous contest.

Total number of QSO in your log is 57, Including 0 QSO with errors, Valid QSO - 57
Band  QSOs Dupes Points Mults
160      0     0      0     0
80       0     0      0     0
40       0     0      0     0
20      57     0    117    64
15       0     0      0     0
10       0     0      0     0
======================================
Total   57     0    117    64
Claimed score is 7488 points

I was looking at on-line offers of shielded/foiled network cable and found out it's not that expensive anymore. And with the 'keystone' connectors it looks like it's not that complicated to make neat and very well shielded connections.

But it's always a good plan to check the local electronics hobby shop. We still have one in the center of Utrecht: radio centrum where they had 1 meter and 2 meter patchcables for a very nice price (competitive with on-line shops) right up for grabs. So the first set of short cables that are always in use for gigabit are now s/ftp category 6 cables. I hope this improves radio reception.

I still think I will order longer cable and keystone connectors and holders for the longer cables.

Usernames seen in ssh attempts: 0 1 a a0 adm admin admln agnes ajay apache ask bin byte cactiuser CarpeDiem cisco cs daniel data db2inst1 debian D-Link erp ezrena faxadmin ftp ftpuser glassfish gpadmin guest help jesus lancer maile mailers marifer maronique media mis mysql nodeclient ooooooooo opuser oracle perl personnel pi pig PlcmSpIp postmaster postpone remote root roote rppt sales shop student support test testing ts ts3 turbo ubnt ubuntu user vnc wildfly willy xbmc And the '' username (empty string). By numbers root has the highest number of attempts.

Today I had planned to dig deep into the sources of the HF interference by switching off the electricity in the whole house and seeing what difference that would make and if it did, search for sources.

I used the 10-20-40 meter band endfed outside, and the 10-20 meter dipole inside. The conclusions are mixed:

• The 40 meter band (that I can only use on the endfed) is not influenced at all by switching off the power.
• The 20 meter band on the dipole gets somewhat less noise when the power is down.
• The 20 meter band on the endfed gets the same amount of noise when the power is down.
• The 10 meter band on the dipole gets no noise at all when the power is down. Change from S8 noise to S0 noise.
• The 10 meter band on the endfed gets 2-3 points less noise when the power is down.

So for the 10 meter band and less for the 20 meter band it was good to search in the house for sources of the noise. Found:

• The lights in the attic
• The UPS for the server
• The netgear switch downstairs when ports become active. The switch upstairs probably too, but it's behind the UPS, so interference from the UPS showed up first
• The wireless accesspoint downstairs

So the problem sources that I can't switch off easily are all part of the home network. My current theory is that 10 meter seems to be affected by gigabit network. My experience is that transmitting on 10 meter indoors causes a network outage.

The home network is all Cat-5E at the moment, unshielded twisted pair. It seems an upgrade to s/ftp is in order (with foil and braided wire, the same I do for antenna cable).

The thing is that with the current solar cycle 10 meter use is very rare. I haven't made a contact yet in that band in 2017.

Interesting error message today:

Jan  1 01:01:02 ritchie CRON[1834]: pam_unix(cron:account): account koos has password changed in future

But it is caused by the system realtimeclock being completely wrong and assuming the date is 1 January 1990 or something. It probably needs a new battery. Or maybe a whole new system, this is from the system ritchie that started life as the wardriving box which was bought in 2008.

This evening the only amateur satellite pass at a reasonable time was by the XW-2A satellite, part of CAMSAT XW-2 Satellites - amsat UK and I only heard weak signals which sounded like other radio amateurs tuning their transmitters/receivers but I never heard something like a voice. Or my own signal when I tried transmitting.

Passes of amateur satellites aren't always at times that are compatible with other things happening. But the discussion about AO-85 on the amsat-bb mailing list also had some details about the satellite and I also found AO-85 Twist Trick and Other Hints - Spacecomms which explains:

Apparently the epoxy caused a change in impedance which essentially “detuned” the antenna. It makes the bird appear deaf. A workaround is to twist the Arrow antenna 90 degrees when you transmit. That is, rotate the antenna until the receive signal is “peaked” and then rotate it 90 degrees when you transmit and back again to receive.

The downside to this is if you’re working full duplex when you rotate the antenna 90 degrees to transmit you will often lose the downlink signal and not be able to hear yourself. In my experience I only have to do the twist trick in the beginning and end of the pass when the bird is farthest away.

Another fix is to just use more power, but if you only have an HT that’s usually not an option.

This, combined with the frequencies up and down being slightly different from the planned frequencies explains the weak signals I hear upon receiving and the difficulty I had getting into the satellite.

This evening had a pass of AO-85 which did not leave me time to drag out the whole setup, but I was able to bring the arrow antenna and a handheld radio to check reception to see if the frequency was correct, including doppler correction. It was correct, but reception is indeed quite sensitive to the orientation of the arrow antenna.

We zijn verzekerd bij Unive, en daarover ontvang ik een mailtje:

Subject: Document(en) bij uw pakket xxxxxxxx

Geachte heer ..

Hierbij ontvangt u het overzicht van uw verzekeringspakket. Wilt u
controleren of de gegevens juist zijn?

Mijn eerste gedachte was om het attachment direct naar een analysestraat voor malware te sturen, maar we zijn inderdaad bij hun verzekerd en het mailtje was gericht aan het adres wat ik gebruik om met Unive te communiceren. Alleen lijkt het subject wel erg op de mailtjes die ik zie met de nieuwste ransomware.

Dus toch maar eens de pdf geopend en daar bleek ook een 'acceptgiro' in te zitten. Dus het was nogal vitaal om dat bestand te openen en door te lezen.

Ik wilde dus Unive op de hoogte stellen van het feit dat ze nogal onhandig communiceren. In het e-mail bericht staat:

Heeft u nog vragen of opmerkingen, neem dan gerust [2]contact met ons op.

Met een verwijzing naar https://www.unive.nl/klantenservice. Alleen als ik daar mijn verbetersuggestie probeer in te voeren moet ik om het bericht te mogen versturen ook perse een adres en een geboortedatum geven, en is het optioneel om zelfs mijn burgerservicenummer te geven.

Voor het verwerken van mijn suggestie zijn die gegevens niet nodig en het zou dus heel handig zijn als er een contactoptie was waarbij die gegevens niet gevraagd worden. Dit is geen privacy by design.

Vandaag in de spambox:

Weet je nog dat ik je een tijdje geleden vertelde dat ik op zoek was naar een date via internet? Jeetje, wat was dat moeilijk, ofwel kwam ik uit op een of andere vrouw die zichzelf voor iemand anders uitgaf, ofwel stond ik daar op een date voor niks! Vorige week dan uiteindelijk via via nog een laatste keer geprobeerd en me aangemeld op deze http://track.trqq.us/index.php/campaigns/wl1097ca0152e/track-url/zo129aq31z3j1/12ba15d9a417e1723e8f4327c6cd1e9a3ea34c18 gratis datingsite

Leuke poging tot aan de tracking-url...

I decided to share my woes of the receive side going deaf (receiving nothing) when I transmit with the amsat-bb mailing list, together with a description of the whole setup. The suggestion came from Eduardo PY2RN to not use a preamp and have filtering so the transmitted signal cannot get into the receiving side.

I pondered this for a while and realised I already have a filter: the diplexer on the arrow antenna. So to receive on 2 meter and transmit on 70cm I connect the transmitting radio to the 70cm antenna and connect the receiving radio (the rtl-sdr) to the 2 meter antenna via the diplexer, and put a 50 ohms terminating resistor on the 70cm connector of the diplexer to make sure it still shows the right impedance.

In a simple test this works, transmitting now has a lot less influence on the rtl-sdr (it's not completely gone yet). I haven't had a good satellite pass yet to try this out.

In my project to receive amateur satellites with the rtl-sdr I noticed the sdr itself has quite a frequency error as noted in Going full duplex with amateur satellites, part 5 : first test of the amplifier with RTL-SDR.

Using the PI2NOS output frequency I ended up at an error of 54 ppm so I entered that in gqrx. But to be really sure there is a program named kalibrate-rtl available via GitHub - steve-m/kalibrate-rtl: fork of http://thre.at/kalibrate/ for use with rtl-sdr devices.

I had some trouble finding the right way to use this program so I am sharing my steps here. First try to guess the error by using a known frequency such as a local repeater (especially when they mention using GPS to maintain frequency) or a broadcast FM station.

First step with kalibrate-sdr is to scan for GSM channels which are strong enough. I noticed in later runs that I really need to add the first guessed frequency error, otherwise it will not find the GSM channels at all.

koos@kernighan:~/radiowork/kalibrate-rtl/src$ ./kal -s GSM900 -e 54
Found 1 device(s):
  0:  Generic RTL2832U OEM

Using device 0: Generic RTL2832U OEM
Found Rafael Micro R820T tuner
Exact sample rate is: 270833.002142 Hz
[R82XX] PLL not locked!
kal: Scanning for GSM-900 base stations.
GSM-900:
        chan: 8 (936.6MHz + 724Hz)      power: 67277.85
        chan: 17 (938.4MHz + 606Hz)     power: 36428.54

Second step with kalibrate-sdr is to select a GSM channel to use for the calibration run. I selected channel 8 which looks quite active.

koos@kernighan:~/radiowork/kalibrate-rtl/src$ ./kal -e 54 -c 8
Found 1 device(s):
  0:  Generic RTL2832U OEM

Using device 0: Generic RTL2832U OEM
Found Rafael Micro R820T tuner
Exact sample rate is: 270833.002142 Hz
[R82XX] PLL not locked!
kal: Calculating clock frequency offset.
Using GSM-900 channel 8 (936.6MHz)
average         [min, max]      (range, stddev)
+ 169Hz         [85, 251]       (166, 49.119198)
overruns: 0
not found: 0
average absolute error: 53.820 ppm

And only in that step you get the output with the calculated frequency error.

Update: Doing this calibration is also a good idea for the stick running the ads-b receiver. That came out to -30 ppm and using that factor makes dump1090 receive signals from greater distances.

This evening had a Fox-1A (AO-85) pass at a reasonable time so I decided to drag the entire setup outside and try my luck at a qso. Reception of Fox-1A was bad (maybe I'm somewhat off-frequency) and the major dissapointment was that the receiving side on 2 meter via sdr got deaf when I was transmitting on 70 centimeter. That's not supposed to happen, the whole reason for the full-duplex setup was to be able to hear myself on the downlink.

Anyway, the recording of downlink audio went fine this time so there is a full recording of what I heard. It was a Northwest-Southeast pass which means it took a while before I heard anything because northwest is over the houses. Callsigns heard in this pass: DO3EXE, IZ5ILX, 9A2EY, IZ3KLF, Something with F2D I completely can't decode and "Mr Olla".

My best guess would be a retry on SO-50, FO-29 or AO-73.