News items for tag electronics - Koos van den Hout

2018-08-12 Making the HP DPS-700GB power supply less noisy 1 month ago
The HP DPS-700 GB power supply adapted to feed the linear amplifier has no own internal fans so I connected a recycled 50mm PC fan. Which runs at full speed which is a lot of noise. I ordered a 12 volt fan control module on-line so it can run slower and keep the noise down a bit.

I'll probably replace the current fan with an 80mm PC fan and set a low minimum speed. The air has to move as the power supply has no internal fans and is quite good at a thermal shutdown. But as long as things don't get warm it would be nice to reduce the noise as this was very noisy.
Read the rest of Making the HP DPS-700GB power supply less noisy

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2018-08-06 Rich chunky amps from a HP DPS-700 GB server power supply 1 month ago
At a hamfest a scouting group was offering a HP DPS-700 GB power supply for the nice sum of 5 euro. A quick search with google found information about the pinout so I bought it. This is a power supply that can deliver 56 Ampere at 12 Volts, and the 12 Volts can be adjusted upwards somewhat.

As usual with projects like this the power supply lived in the stack of projects for a while, but today I got around to testing it. Finding the pinout again was a bit hard, but I found the pins again at HP DPS-700GB 80mm fan shroud - Thingiverse which includes the simple modification to make the output voltage go up.

As this power supply has no internal fans and will stop fast due to internal overheating if not cooled, I set it up with a recycled computer fan. Power supplies like this will always be active in systems with enough fans to push air through the whole chassis.

The first test gave me 12.1 Volt. After adding a 1.5 kOhm resistor it went to 13.27 Volt. In theory the maximum current may have dropped as a result of this modification, but my best guess is that it can still deliver 50 Ampere.

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2018-04-24 Building my own balun, part 7: Better measurements of the result 5 months ago
Homemade balun version 2 SWR scan 1-60 MHz
Homemade balun version 2 SWR scan 1-60 MHz 20180424
Homemade balun version 2 SWR scan 10 meter band
Homemade balun version 2 SWR scan 10 meter band 20180424
Homemade balun version 2 SWR scan 20 meter band
Homemade balun version 2 SWR scan 20 meter band 20180424
Time to do measurements of the revised attic antenna. And now with a voltage balun with more windings the balun is working better, showing ok SWR values. A nice optimum in the middle of the 20 meter band (although I originally wanted that optimum near the digital mode part) and a nice optimum in the 10 meter band (also somewhat higher than originally planned). Comparing them to the original measurements show an increase in frequency in both SWR curves.

So I consider this a good result! Time to get it on the air and make contacts again.

Next step, working on an outside dipole with the Fritzel balun.
Read the rest of Building my own balun, part 7: Better measurements of the result

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2018-04-23 Building my own balun, part 6: Redo and some success: a working antenna again 5 months ago
After the previous measurements showed the balun and dipole under the roof weren't acting as a perfect combination. So time to do a few things better: more windings, less leftover wire and a switch to a voltage balun. Yes, other sources indicate a current balun is better, but I decided otherwise. The Fritzel balun turned out to be a voltage balun after I removed it from the dipole antenna.

Balun project version 2 in case So I used the instructions at 1:1 voltage balun by VK6YSF to rebuild it as a voltage balun and I made sure the wires were shorter in the end. Getting the shorter wires in the right places in the case did get me some slightly burned fingers!

Success is currently defined as "I can transmit a carrier on the 20 meter or 10 meter band and the SWR meter of my radio only goes up a few segments" which isn't very scientific, I will need to do the rest of the measurements with the SWR meter to be sure.
Read the rest of Building my own balun, part 6: Redo and some success: a working antenna again

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2018-04-16 Building my own balun, part 5: First tests of the result 5 months ago
Homemade balun SWR scan 1-60 MHz
Homemade balun SWR scan 1-60 MHz 20180415
Homemade balun SWR scan 10 meter band
Homemade balun SWR scan 10 meter band 20180415
Homemade balun SWR scan 20 meter band
Homemade balun SWR scan 20 meter band 20180415
So I removed the old balun and installed the one I made. Removing the old one wasn't easy: the Fritzel balun has a cover over the SO239 connector which makes the heavy duty connector I used very hard to unscrew. So I had to break bits of that cover to get the needed access. And the connector ended with a lot more scratches from my attempts to get access to it.

But now the balun is replaced, and measured. And it looks like some things have changed now causing the antenna to be 'mistuned'.

Update: Just some measurements and thinking: adding the big common mode choke in the mix makes the combination show better SWR curves (still not what I want) but with the frequency with the best SWR still too low. This suggests (to me) two things: I need more windings on the ferrite core and less extra wire length from the core to the connectors. Time for a rebuild.
Read the rest of Building my own balun, part 5: First tests of the result

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2018-04-15 Building my own balun, part 4: Deciding on where to put dipole ends and finishing it 5 months ago
Balun, case and ferrite core Balun in open case I finally decided where to put the holes in the case for the dipole ends of the balun. This took some serious pondering!

I made those holes, put screws through them and wound the ferrite core with enamelled copper wire. To guess the needed length of wire I first wound it with packing rope, made a small knot at the point where it was enough and unwound the rope to measure the length I used and took a bit longer wire.

Using sanding paper I removed the enamel isolation from the ends of the wires and used soldering tin on it.

Other parts of this project:

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2018-04-04 Building my own balun, part 3: First work on the case 5 months ago
Balun project case Balun project case The first work on the balun case was placing the SO239 socket. This included drilling a hole in the case of the right size and at the right position. Figuring out where to put it was mostly influenced by the fact that the ferrite core has to be placed inside the case and I wanted the SO239 socket, the ferrite core and the output terminals not all jammed together. So the SO239 socket was not going to be in the center. For this my new caliper was a useful tool and I measured the inside size and the wanted location of the socket. And I figured out I could drill a 16mm hole and the SO239 socket would fit inside while leaving enough room for the mounting flange.

Holes were drilled and things worked out fine, so the SO239 socket is now mounted. After checking the future location I realized I will have to mount the balun with the SO239 socket facing downwards because the antenna cable is quite heavy. This has to be taken into account with the next steps.

Other parts of this project:

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2018-04-04 Building my own balun, part 2: measuring the 'old' balun 5 months ago
Fritzel balun SWR scan 1-60 MHz 20180325
Fritzel balun SWR scan 1-60 MHz 20180325
Fritzel balun SWR scan 10 meter band 20180325
Fritzel balun SWR scan 10 meter band 20180325
Fritzel balun SWR scan 20 meter band 20180325
Fritzel balun SWR scan 20 meter band 20180325
Since I want to replace a balun that has been up there for ages I want to be able to compare the two. So I used the antenna analyzer to get graphs of the SWR over the whole possible range (1-60 MHz) and on the amateur bands it was built for: the 10 meter band and the 20 meter band.

There was a very interesting difference with the earlier results on the 10 meter band when I first tested the SARK100 antenna analyzer from Linux. The 10 meter band dipole probably moved a bit or something else changed.
Read the rest of Building my own balun, part 2: measuring the 'old' balun

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2018-03-19 Building my own balun, part 1: idea and parts needed 6 months ago
I was considering hanging a dipole antenna outside. This would need a balun and I realized that I have a good outdoor-capable balun hanging in the attic. It's a Fritzel 1005 1:1 current balun which is good up to 300 watts power.

I am not going to use 300 watts under the roof close to other equipment and the balun there does not need to be rain proof. So the idea was born to build a smaller balun for use under the roof and have the Fritzel balun available for outdoor use.

And last Saturday was a hamfest (radio onderdelenmarkt Rosmalen) so I had an idea of things I wanted for this project.

Parts needed for a current balun:
  • A ferrite core with the right specifications
  • Wire with enamel coating
  • An SO239 socket
  • Terminals for connecting the dipole wires
  • A case
The various collections of electronics parts only missed the SO239 socket and a case. Those were found at the hamfest for a nice price.

The choice of design is a current balun or a voltage balun. I had to do some searching to find a good comparison between the two, and DX engineering has one at Baluns: Choosing the Correct Balun - DX Engineering which has:
Current baluns, rather than voltage baluns, should be used whenever possible. Current baluns provide better balance and often have lower loss. Current baluns, especially 1:1 ratio baluns, tolerate load impedance and balance variations much better than voltage baluns.
Some searches found good explanations of building your own baluns, I found a very clear explanation at VK6YSF project page.

So I'm building a current balun, and when it's finished enough to test it I will measure how it is doing. I have the tools like the SARK100 antenna analyzer that I can control from Linux and a dummy load so I can check everything.
Read the rest of Building my own balun, part 1: idea and parts needed

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2017-09-08 I built a common mode choke 1 year ago
After the problems with the laptop controlling the radio when I participated in the SCC RTTY contest 2017 I decided to build a common mode choke. This is a filter that should keep the radio frequency signals at the side of the antenna.

Based on the simple design with a piece of PVC pipe with 8 windings of Aircell-7 coax I still had lying around. The PVC pipe was donated by a fellow radio amateur who had it in his junkbox.

I drew a pencil line on the pipe, decided where to drill holes for the coax cable (using a 16 millimeter drill) and where to drill holes for tiewraps to hold the coax. After drilling the holes it was a matter of winding the coax correctly, mounting the cable with tiewraps and soldering the connectors to the cable.

In the first testing the filter worked fine, completely stopping the interference to the keyboard of my "shack computer" and even reducing incoming noise on the 10 meter band.
Common mode choke: materials - KvdHout on FlickrCommon mode choke: materials
Common mode choke: finding where to drill holes - KvdHout on FlickrCommon mode choke: finding where to drill holes
Common mode choke: holes drilled - KvdHout on FlickrCommon mode choke: holes drilled
Common mode choke: cable mounted - KvdHout on FlickrCommon mode choke: cable mounted
Common mode choke: connectors done - KvdHout on FlickrCommon mode choke: connectors done

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2017-09-08 I finished the linked dipole and tested it 1 year ago
I realized today I never wrote an article about finishing the linked dipole kit I bought a year ago and started making my own dipole from Linked dipole portable HF antenna kit.

I used the SARK100 antenna analyzer to test it on each band: first 15 meter, after that 20 meter and I finished with 40 meter. I did 15 and 20 meter on two separate meetings at my radio club and 40 meter in a park near our home. As mentioned by others you need to take the time to tune this antenna to the right length. Each band took me about 2 hours which turned out to be what I could do in one evening at the radio club.

The proof is always the first contact and that happened when I brought it on our holiday to Germany and Austria. The tree behind our tent at the campsite in Austria was not high enough to support the 40 meter length of the antenna but I just set it up for 20 meters and that worked fine. It's remarkable how forgiving this antenna is after tuning. I just set up something resembling an inverted V and my radio found it near perfect, very little reading on the SWR meter.

First completed contact was with a radio amateur at the same campsite so that wasn't very hard. I did hear a Dutch radio amateur using a serious amplifier to try to reach me but lacking output power he did not hear my answer.

Anyway, project officially finished.

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2017-07-03 Reboots of the FT-857 radio 1 year ago
The last week I had a problem with the FT-857 radio rebooting when I started transmitting in digital radio modes (PSK31 or JT65). The reboot showed as the radio giving the standard beep and the display and backlight switching off and on. Searching for clues suggested that some form of radio frequency interference would probably be the source.

So I wondered what I changed recently around the radio and remembered I changed something in the power distribution to have connectors available for powering my SARK100 antenna analyzer with a 12 volt battery.

Reseating all those power connectors and fixing some wires seems to have stopped the problem.

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2017-05-22 I bought a SARK100 antenna analyzer 1 year ago
My sark100 antenna analyzer
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, build it and measure / adjust it until it does what I want.

It's a good thing I can easily calculate linked dipoles at Various tools for SOTA purposes. My plan is to build a 15-20-40 meter band dipole. The selection of bands is because outdoors I will use less digital modes and 40 meters is the longest size for a dipole that is usable to set up. The angle of the dipole and therefore the height of the centerpoint also has an influence on the antenna. But I don't know how high the tree will be, so I will have to make a guess.

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2017-05-14 Upgrading the home network to shielded/foiled cable (s/ftp) 1 year ago
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.

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2017-04-29 Using kalibrate-rtl to calibrate the rtl-sdr frequency 1 year ago
In my project to receive amateur satellites with the rtl-sdr I noticed the sdr itself has a considerable 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.

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2017-04-14 Going full duplex with amateur satellites, part 4 : amplifier built into the case 1 year ago
Today I had some time to work on the metal case for the amplifier I bought for receiving amateur satellites. I've never been good at metalwork but I think I did ok. First I made sure the place I wanted to put the holes was chosen correctly, taking the size of connectors into account. Especially with metalwork it's "measure twice, cut once". Next I drilled holes with a drill for metalwork (HSS) and used a file for metalwork to make the holes bigger. I visited the local electronics shop to get a small switch for switching the battery power on and off and added a hole for the switch. In the end the amplifier and the cables are mounted inside the case and there is a bnc connector for the Arrow antenna on one side and an SMA connector for the cable to the RTL-SDR stick on the other side.

Battery added for amplifier in metal case - KvdHout on FlickrBattery added for amplifier in metal case

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2017-04-12 Trying the mini-whip as reception antenna 1 year ago
Recently I talked to a fellow radio amateur about my HF reception woes at home and he suggested trying the mini-whip antenna I built a few years ago as reception antenna, using an automatic switch to switch between the transmission and reception antenna.

For the first test I used the mini-whip antenna with the HF downconvertor and an RTL-SDR stick that I bought to receive amateur satellites to check the signal on the computer. The further I move away from the house the better signal I get (less noise, more signals sounding like the amateur radio signals I want). I do notice that when I turn the gain on the RTL-SDR up (or set it to automatic gain) that there is a repeating 'ticking' signal which sounds just like the ticking interference from my own PLC tests.

This could mean that a nearby neighbour has a PLC network without the notches for amateur radio. Or this is just an artefact of the high gain.

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2017-03-29 Going full duplex with amateur satellites, part 3 : metal cases 1 year ago
I was looking for a metal case to put the low(ish) noise amplifier in and maybe the RTL-SDR. The RTL-SDR should also be shielded from the amplifier and from the computer as both RTL-SDR and computer cause their own signals.

The first cheap source of metal cases I could think of was old cigar boxes. Altoid tins are not available here. So I asked someone who I know who smokes cigars who had a number of old metal cigar boxes. Next step, finding the way to get the right holes in the boxes for the SMA and BNC connectors, and for the USB connection to the computer. Ideal would be to lend / find a punch for those holes.

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2017-03-26 Going full-duplex with amateur satellites, part 1: introduction and I bought the hardware 1 year ago
I still want to get active on amateur satellites again, but the main reason is that the amount of work per contact is a lot more than for example in a digimode contest. But I still want to make those 'special' contacts, especially when the amount of local radio noise on HF is bothering me.

One of the most important improvements in making contacts on amateur satellites is working 'full duplex', meaning receiving signals while transmitting. The expensive way to reach that goal is buying a second amateur radio capable of receiving in FM and SSB modes in the 2 meter and 70 centimeter amateur bands and having computer aided tuning so gpredict can control the receiving frequency.

The less expensive way to reach that goal is using software defined radio. The good news is that Gqrx SDR can be controlled by other software which as the page shows is intended for remote control by Gpredict. All I needed now was reception hardware. Since the first RTL-SDR device I bought is always in use for receiving ADS-B signals from airplanes I decided to buy another cheap one to get me started. So it was on the shopping list for a recent visit to a hamfest.

At the hamfest I found a RTL-SDR stick with mcx connector and an mcx to bnc cable. But the same guy also sold cheap low(ish) noise amplifiers with SMA connectors and a 9V battery connector for power. So at one of the booths selling cable assemblies I found an mcx to male sma cable and a female sma to bnc cable, and a male to male sma cable.

The plan is to put this all together in some metal case to shield the lna from the outside world. Maybe also shield the amplifier from the RTL-SDR stick so it won't pick up any extra noise.

Should this work it would be possible to think of an upgrade with better SDR hardware and/or a pre-amplifier at the antenna side.
RTL-SDR stick and BNC cable - KvdHout on FlickrRTL-SDR stick and BNC cable
LNA and extra cables - KvdHout on FlickrLNA and extra cables
Read the rest of Going full-duplex with amateur satellites, part 1: introduction and I bought the hardware

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2017-03-17 Soldeerstift vervangen van soldeerstation 1 year ago
Een tijd geleden heb ik een soldeerstation gekocht van Velleman, een Soldeerstation keramisch 48W VTSSC30. Die gebruik ik ook regelmatig naar alle tevredenheid.

Tot recent het steeds meer moeite ging kosten. De conclusie was uiteindelijk dat de stift aan het verslijten is, wat heel logisch is. Ik was even bang dat ik niet zomaar een losse stift kon krijgen, maar na dat ik deze gekocht had via Conrad blijkt die ook via Radio Centrum verkrijgbaar: Soldeerpunt 1,6mm Velleman VTSSC10/20/30/40 soldeerstation.

Stift vervangen, probleem opgelost. Grappig is dat volgens de Radio Centrum website de originele meegeleverde stift 1.6mm is terwijl ik in het overzicht van Velleman soldeerstiften bij Radio Centrum zie dat ik de 2mm versie had. Misschien moet ik nog eens een 0.8mm punt er bij kopen voor klein soldeerwerk.

Update: Radio Centrum zit dicht bij de winkel waar ik koffie haal, dus ik kwam er langs en heb gelijk een 0.8mm punt aangeschaft. Gelukkig hebben we nog een echte electronica winkel in Utrecht.

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