CQWW WPX Contest, SSB

Call: OH8X
Operator(s): LB3HC, LA7JO, CU2DX, CU2CE
Station: OH8X

Class: M/S HP
QTH: Arcala
Operating Time (hrs): 48

Summary:
 Band  QSOs
------------
  160:   36
   80:  106
   40:  478
   20: 2259
   15: 1082
   10:  178
------------
Total: 4139  Prefixes = 1379  Total Score = 11,906,286

Club: Contest Club Finland

Comments:

Great to be back operating from Arcala now that the SSN is higher! All
operators: LB3HC, LA7JO, CU2DX, CU2CE had a great time and a lot of fun (as
usual from OH8X - Arcala). 

Thanks to OH2BH, OH8NC and OH6KN for hosting us! Also thanks to the rest of the
Arcala team for making this possible!

This time we also had time to take some HD video and wide angle pictures of the
station.

Plusses:
=========
This time we had relatively good conditions up here at 65 degrees north
latitude in the ice and snow.

No significant technical issues were experienced.

This station station is professionally built by the extremely skilled guys in
the Arcala team. Kudos!

The Arcala antenna park is nothing less than extreme.

It was nice running with the new Yaesu FT DX 5000. Yaesu did it again! 

Minuses:
=========
We were likely affected by aurora at several time periods during the contest
that affected rates. We were unable to achieve runs at 40 and 80 to DX
locations and that resulted in that the DX runs was worked on 20 and 15. That
cost us 6-3=3 points per DX QSO and our average QSO points were below target. 

Our target was to beat OH10X from 2011 and we wkd more mults, but somewhat less
QSOs corrected by the QSOs/36*48 factor due to condx and latitude (claimed
score). In fact 40 meter did not give good DX propagation at all.  OH10X is
approx 500 km to the south. 

We lost power due to a power company outage / spike at night and lost control
over all tower rotators and the voice keyer. It took several hours to correct
this.

Summary:
=========
WOW! What a station and what a team. Contesting has got a new meaning.
Updated pictures will be posted at http://www.lb3hc.net

On behalf of the team
LB3HC
Marius

This was a very nice meeting at the Arcala Xtreme Station @ 65 degrees northern latitude. The Arcala team has an approach to amateur radio that is both social, technical, and serious. This time in nice weather with spring temperatures around the corner and snow melting. Check in later. More pictures and video from Arcala will be posted. And also check 3830 for contest results!

The inside details and the chassis can be seen in the above pictures. In the left picture, it can be seen that the designer has used a image sensor that has been designed for the cellphone industry. There is a detachable lens (with threads in some of the sensors used) and the lens is attached to the mainboard via a flexiprint and via a controlled impedance and controlled delay connector. The sensor has the type designation OV9712. It can deliver 1280×800 in 30 fps or 720p WXGA HD format. The sensor has gain control, color balance control, and can even correct distortions caused by optics on die. Here is the datasheet of the sensor: http://www.ovt.com/products/sensor.php?id=29   There is a memory chip and a System On Chip (SOC) on the printed circuit board. The SOC has the designation NT96632BG. This SOC appears to me manufactured by the Taiwanese company Novatek . Their website was slow when I visited it, but here is the link http://www.novatek.com.tw/products/SoCSolutions.asp The manufacturer says this about their chip: “Novatek provides DSC/DV SoC solution, which features high image quality, high performance, excellent digital still image capturing and video streaming capabilities at a cost effective base. It is targeted for the application of VGA to 32M pixel DSC/DV resolutions. It can be easily adapted to many CCD and CMOS sensors with on chip programmable interface timing approach. Novatek’s DSC/DV controller provides sophisticated video processing methods with built-in hardware acceleration pipeline. Hardware H.264 video CODEC is embedded with The HDMI 1.3 Tx.“ A significant feature would be analog low latency video out. Then this camera would be ideal for FPV RC flying.

There is a reliable Ebay source for this camera here: eletoponline365

 
Above the three choke sections can be observed

Above, the measuring setup can be seen. On the right there is a multicore choke that was  tried. It gives a big resistive and inductive peak low in the frequency range. Far more than required. The cost will be high due to the many cores and is not justified. Therefore a 3 + 3 + 2 design was found more optimal.

 
Above the resistive (blue) load to the common mode current, the inductive load (red) to the common mode current and the Q (green) for the choke can be studied. The choke presents around 1000 ohms resistive to HF current in the frequency range of approx 2,5-25 Mhz. Another material could probably have been added to prevent the drop above 25 Mhz. 10 Meter would be a bit marginal for QRO operation with a lot of common mode current.

I wanted to check the load that a ferrite core with a secondary winding presents to the common mode current carrying conductor (the outside of a coax) when set up as a current transformer. The coax runs thru center, the secondary winding could be one or several turns loaded by a R+jø load. 

I did the following S11 measurements with the VNA:

1) No secondary winding is present but the single turn is running thru the core

2) A shorted two turn secondary and an open two turn secondary winding is pulsed on and off to detect a difference

3) Only the primary winding is attached to the calibrated S11 measuring plane. (to measure the self inductance of the single turn in itself)

Above is a similar test setup. The core is an “unknown” Amidon toroid core. The red conductor is the simulated coax common mode current path (a one turn loop). The green conductor is the secondary winding. The load could made by paralleling several resistors in series with the secondary (the blob on the left side, right picture). Note that the measurements below were done with a one turn loop and a short – no resistor. The measurement device is a VNA from DG8SAQ calibrated by O S L  references in the S11 measuring poing (the SMA in the end of the coax from the TX port).  

The left picture shows measurement 1) The mid picture shows measurement 2) the right picture shows measurement 3)

What is interesting to see is that the image to the left shows that this core has some resistive loss as can be seen on the blue trace. The Q is quite low. When there is a secondary winding present, the loss is shorted out but the inductance goes up since the inductance of the secondary is reflected into S11. On the right image it can be seen that there is no resistive loss and a linear inductive reactance caused by the air core inductor (no appreciable drop off or frequency dependent effects, in the measuring frequency range)

What this tells me is that this core probably is not too well suited as a high current measuring setup for frequencies above 160m because it will affect the measuring circuit too much. Not in terms of the R element but because of the +jX element. My analysis says that another core type should be selected. (I may be wrong). Please comment if you have comments or suggestions.

I here describe a wideband HF RF choke design in pictues. The choke covers most of HF from 160m to 10m and will give a resistive part of the impedance R ( R+jX) that should be high enough to not cause overheating of the ferrites. It will also give a significant reacive load, but the resistive load cannot be cancelled by capacitive effects easily. The 9 + 1 core design above will give the resistance shown on the blue trace in the image to the right above. The other traces (red, green, pink) shows  5, 4, 3 turn designs that was first tried. Note that the fewer # of cores in the choke, the higher up in frequency the resistance peak occurs. Note the single external series core with two turns. That single core takes care of extending the resistance up in frequency above the lower peak (the peak that goes out of the graticule to the upper left). The material is the Fair-Rite 2643167851 material.

Today I did some further measurements on the same Fair-Rite material as the other post (Fair-Rite 2643167851). I did the measurements with a calibrated open, short, 50 ohm load S11 measurement. The green trace is the resistive part of the impedance, the red trace is the reactive part of the impedance and the blue trace is the unloaded Q (ratio stored energy in the magnetic field in the core and windings to lost energy in the effective series resitance). As expected, the Q is one when the green and red traces cross each other. This material is not useable as a regular coil for energy storage (high Q, filters and such) over approx 15 Mhz. Below 15 MHz the Q can be quite high, however. This core is probably very good as a dampening material for RFI applications as GM3SEK has indicated. For High power operation when coax common mode current causes problems I think this core may be good. The reason is that the resistive component (real component) of the impedance is dominant. This means that even if a capacitive reactance cancels the inductive reactance, the resistive part of the impedance is still always present. This can be seen from the green trace above. Center of the plot is approx 300Mc/sek. It also rises with QRG up around 450 Mc/sec. At 2 meters and 70 centimeters wavelength it looks like even one turn on a coax (in a low impedance point of the coax!) this choke will do some good. At HF, with more turns it is possible to achieve 1000 ohms over a fairly large range.

Above is a three choke setup

The blue trace above is the real Z ( R ) plotted from 0-30 MHz. The scale is 480 ohms/div. As you can see the material gives a resistance over a fairly large BW well over 1000 ohms peaking around 5K ohms resistive at the low frequency range. However over approx 18 Mhz, the resistive component is not that great. For QRO operation on 15 meter and 10 meter some further measures should be taken if RF currents are high.

Here is a three stage RF-choke setup. First the three element RF-choke, then a one element RF-choke and a two element RF-choke with the material stacked on top.

Note that the scale here is 620 ohms/div. The measurements show that the three in line setup didnt change the resistive part of the choke a lot. This may indicate that for QRGs over 18-20 MHz, a material with more loss in that frequency range could be found. I am later going to experiment with different winding diameters and cable diameters to see if that will change the resistive elements in the upper parts of the HF spectrum.

The procedure I used to find the velocity factor of the balanced transmission line was to first measure a length of the feedline with a tape measure. Then I connected the MFJ-259 and found the frequency where the lowest reactance could be measured. (See pic two from left on the upper row above. You can see that the X is very low). This was done in the mode of the MFJ-259 where it is possible to measure both R and X. This is the quarter wave frequency of the line when the wave propagates in the line – not in the free air (“ether”). Then I calculated that frequency back to the wavelength with  y=300/f. I then divided the tape measure length by the calculated length and came to a velocity factor of 0,89. This is the ratio of the wavelength in free air and the wavelength in the transmission line. This is directly related to the propagation speed of the line when it operates in transmission line mode. From that I calculated the required length of the matching transformer and the approximate tapping point on that transformer to reach 50 ohms. Please note that you cannot use the velocity factor of the transmission line to calculate the required length of the antenna (only the matching section), since the RF currents on the two folded legs on the antenna are in phase and therefore the one lead is coupled to the ether and not to the other lead.

The picture above shows the SWR as measured with my vector network analyzer from DG8SAQ. The markers on the right side shows a 1:2 SWR bandwidth of 118,5 to 128,6 Mc/s which is OK. The reference level is 1:1 SWR. This level is lifted one division for clarity. (I think the Mc/s  is a cool way to express frequency by the way.)

Here my DG8SAQ1 kc/s to 1,3 Gc/s VNA is shown. It is connected to my PC via USB.

Conclusion: a combination of the MFJ-259, the DG8SAQ vector network analyzer, some balanced line and some coax can be used to make a good collinear airband antenna in less than one our at a cost of a few dollars. The antenna was screwed to a wooden section of my roof by a small screw by the way and can be removed in approx 2 minutes.

This is actually a nice amplifier that should be quite easy to build for the experienced engineer and experimenter. The benefit of using lower anode voltages is that the tank circuit capacitors can be of a low cost variable type. The PSU can also be integrated more easily in the same cabinet as the amplifier circuit. You can check out more information over at PA0FRI’s webpages: http://pa0fri.home.xs4all.nl/Lineairs/Frinear150/fri150eng.htm