Friday, November 25, 2016

IFFY STM L7805CV devices from Farnell

This week I started work on my my triband 28V 4/6/2m amplifier using a Kalmus module I got off ebay. It needs a PIC controller which runs off 5V so I ordered twelve STM made L7805CV from Farnell which should give 5V output with up to 35V input.

 I connected up the PCB and LCD and turned it on. The LCD got very bright and the pic refused to work. Remembering the addage "99% of all problems are power supply related" I measured the voltage coming out of the L7805. It was 7.88V!  Replaced the regulator with another one from the same batch. 7.90V. As an experiment I ran the regulator off 13.8V. It gave 5.05V which is fine.
Looking in the component collection i found an old STM L7805. Soldered that in and it gave 5V with both 13.8V and 28V input. The only difference(apart from the date code) between the old and new regulators was that the new one said "STM CHN" the old one said just "STM". Enough said!

I contacted Farnell, who apologised and were persuaded to replace the iffy regulators with the Fairchild LM7805CT. These have now arrived and work fine off 28V

Moral: Measure the output of regulators before applying to circuits!

Sunday, November 6, 2016

LF season approaching

As the winter is approaching it was time to think LF again. When I bought the main parts for the MF amplifier from Dave G0MRF at the HF convention I also ordered one of his preamp kits. I managed to squeeze it into a small pomona box, time to try it out

Initially I connected it to my Alpha Delta DX-EE and ANAN-10 and left it receiving WSPR using K1JT's new1.7.0RC2 WSJT-X software. It seemed to do well:

Time Call dB Loc Power km
18:22 G4FTC -21 IO91pi 2 137
18:36 PA0A -24 JO33de 1 591
18:38 LA8AV -28 JO59cs 5 1151
19:56 G3WCE -29 JO02pt 1 255
23:52 F1AFJ -27 JN06ht 1 625
00:46 DJ0ABR -29 JN68nt 0.2 1148
00:54 G8HUH -19 IO81mg 1 103
01:16 PA3ABK/2 -25 JO21it 0.5 481

The preamp reduced the LOS droitwich 198kHz on my system.

During the evening  I wondered what was on 136kHz. So I dug out my old G0MRF 136khz preamp and let it run for a short period, while, again connected it to my Alpha Delta DX-EE and ANAN-10 receiving WSPR decoded 2 stations

Time Call dB Loc Power km
22:00 G8HUH -20 IO81mg 0.1 103
22:04 2E0ILY -12 IO82qv 0.01 91

Thursday, September 1, 2016

FAKE AD4351 in AD4351 Signal Generator?

Having got the signal generator from ebay seller ayanhu81 running it was time to measure Phase noise. I decided to start at the low frequency end, so 42MHz was chosen. The controller was set to this frequency and the lock light came on. However, looking on the spectrum analyser no signal was found. Winding out the span a signal was found at 2668MHz (42x64), very strange! Next 116MHz was tried. The controller was set to 116MHz and the lock light came on.  No signal was found at 116MHz but a signal was found at 3712MHz (116X32). I next tried 144,432, 1296 and 2320MHz and the output was produced on the expected frequency. Checking further the IC only worked correctly above 137MHz

As a check I used the AD435x software tool to tell me what the register values should be for 42 and 116MHz and modified the arduino software to load the hex values directly, but still got 2668 and 372MHz. Its not the code, its a problem with the chip

Looking ath the Analog Devices datasheet for the AD4351 it has a divide by 64 and divide by 32 circuit in the chip, which my IC apparently didnt have. I checked the markings on the chip and it said AD4351. I did notice from it's datasheet that the AD4350 does not have these dividers, behaving exactly as my AD4351 was doing currently. Obviously my board had an out of specification AD4351 or a mislabelled AD4350

At this point G4JNT made a post on the UK microwave reflector that he was experiencing exactly the same issue with exactly the same module from the same Chinese supplier

I have raised a "not as described" case with ebay against the seller. He was forced to refund the cost of the module!

Moral: You get what you pay for!

Saturday, August 13, 2016

KR600RC Maintenance

A few weeks ago I uncovered the Rotator and the control box for my KR600RC Rotator. Connecting it together and powering it up resulted in a lot of whirring from the rotator and only clockwise movement. Removing the cover the reason for the whirring was obvious; the drive band had perished.  I searched the web for the a replacement there was no obvious source. However there was a hint from the VKL reflector that the rubber nitrile band was a #29. Web Research showed that in the UK this is called a BS029, which were available on EBAY costing  £5 for 10, so 10 were ordered

The reason for no counter clockwise was also investigated. The reason was because the NC contact on the clockwise switch, through which the counterclockwise switch gets its power, was open circuit. Note that the 2 switches are different; the clockwise is DPDT (6 pins) , the anticlockwise is DPST (4 pins). Researching a replacement switch, I found someone was selling refurbished ones in Australia, so it must be possible to take them apart!

The replacement bands arrived last week so it was time to start repairs. First the rubber feet were taken off. The cover was then removed and the front panel detached. The gear train then had to be dismantled, by removing the calibrated bezel screws to get to the screws holding the metal cover holding the gears in place!) to get the band in place. Note that the rubber band goes round 3 axles to maintain tension

Powering up the indicator then worked properly. The broken switch was then taken apart by releasing the 4 lugs. I noticed that the 2 contacts had slightly different profiles. The non contacting contact was then removed and bent into a shape matching the working contact. The switch was then reassembled and was now found to be performing properly. Job done!

My only concern is how robust the controller is for mountaintop operation; I can see building an all digital controller with LCD display coming up!

Saturday, August 6, 2016

ADF4351 signal generator

Although I have a portable signal generator using the SI570 that can get to 200MHz I needed something that goes a bit higher. Looking on ebay I found some modules that cover 35 MHz to 4400MHz using the ADF4531 for 20GBP so I ordered one (auction 172152204149 by ayanhu81)

It took 4 weeks to arrive. The next question was how to control the module. An internet search revealed a design by F1CJN here  using an Arduino UNO and LCD shield with buttons from, which I did not have. However I remembered in my collection I already had a similar LCD/Switch unit from adafruit This would need some code modification, time to remember how arduino's worked. It was not too hard as Adafruit provide the libraries and examples for this unit on their web site. The biggest issue was as my switch reading used SPI not the A/D converter of the original design it was much faster resulting in much keybouncing.  Some strategically placed delays stopped that issue.

I now have it working. Listening to the signal on 144MHz and 432MHz it sounds OK, if a little off frequency due to the cheap on board reference (6kHz low at 432.2MHz) but as the board has an external reference input that is not an issue. Next to take a look at the output spectrum, which is reputed not to be too good at lower frequency, then to put it in a box.


Monday, July 25, 2016

70MHz Trophy

Enthused about 4m from previous outings we decided to visit British (IO81KR) again. We were late starting by 30 minutes by eating cake and coffee before departing to the site!. There was mist/rain/drizzle for the whole contest. Again we used the K3S and the Anglian transverter to drive the I0JXX dualband amplifier. The antenna was the 5 ele Powabeam at 6m,

The only equipment issue was computer related. The K3S just has one USB connection to the computer (no audio leads). For the first 30 minutes on every speech peak the virtual serial port and the K3S soundcards would be removed from the computer and reappear on receive. After a while there was a warning that the device was disabled as it was unstable. Not having had this issue on previous 4m events I took a look at the USB lead. I had taken the first one from the bag; a thin black lead. Looking further I found a thicker lead with clear cover that showed a decent braid. Changing to that cable, the issue went away!
In a change to  normal, there were numerous stations QRV up north, in IO84 and 94. This activity allowed us to confirm that the site is good to the North, we dont normally work much up there as there is no activity! The loudest signal was from GM4ZUK/P in IO86. Although two stations were worked in GU, there was not even a hint of a GJ station or GD. Being called by GI4OPH in the last hour was a welcome surprise/ 98 QSOs were had with the best DX being PA4VHF in JO32 at 640km

Saturday, June 4, 2016

June 70MHz UKAC

After the success during the previous Sunday's 4m contest, thoughts turned to the 4m UKAC the following Tuesday evening. Blorenge is much more hospitable at this time of week and it was much easier to get to directly after work than British Mountain

This time we used Rogers Van to support the 5 ele Powabeam at 20' Again the K3S drove the Anglian transverter then the I0JXX amplifier module, all operated from the Honda Jazz.

There was some DX heard while setting up from EA and IC8, but it disappeared as the contest started. Conditions on tropo were poor, but we ploughed on, listening around between qsos. We found EA6SX who we worked at 1442km as the best DX. After this excitement the search for multipliers continued. No continental DX was worked. Northern English squares were well represented but despite calling a lot that way, there were no sign of GM stations. 109 QSOS were made in total

Nice Sunset

The results have been published very speedily... within 12 hours of the entry deadline, AND the writeup contained more details than "the next contest is on xx/xx/2016! Looks like only our station worked the Sporadic-E





Friday, June 3, 2016

70MHz Cumulative Contest

Having finally  finished integrating my I0JXX dual band 50/70MHz amplifier it needed trying out. The contest calendar showed a 2 hour 4m (2nd cumulative) contest so we decided to give it a try. Blorenge is no place to be on a Bank holiday Sunday so an alternative was needed. Roger suggested British Mountain which was a bit more remote. I had never been there so I went there via his house, so i could follow him. The route was challenging for both vehicles. As we neared the destination we noted a vertical antenna and a tent, which caused concern, Dropping by and introducing ourselves we found they were CBers so we should have no trouble to us on 70MHz. We moved 100m along the road and setup the station. The 5 element Powabeam was put on 25' of pole with guys. The rest of the station was the K3S (on its first outing) and my G4DDK Anglian Transverter. We also got to try the audio boxes I had made which allows the operator and logger to choose any combination of main and sub RX audio

When the antenna was connected the band was full of wideband signals. Sporadic-E was in progress, the band was occupied by FM broadcast stations from Eastern Europe. SQ8EP was worked before the contest, but during the contest, despite the broadcast SP-E signals there was no SP-E dx available, the best dx was PF7M. The Northern English squares were well represented but despite calling a lot that way there were no sign of GM stations. 71 QSOS were made in total.


A friend of a friend stumbled across a youtube video from visitors to the CB station wondering what was going on at the white van up the road from the cb station! The video is here   The marauding sheep timestamp the recording time

Saturday, April 2, 2016

The K3S must be working alright on 475kHz!

Having done the K3S upgrades for 475kHz see here it was time for DX.  I was duly rewarded with my First transatlantic WSPR decodes of the year using the K3S and the PA0RDT whip in the loft:-

Timestamp           Call MHz         SNR Drift Grid          Pwr  km
2016-04-01 23:52 G3XIZ     0.475785 -24 -1 IO92ub 0.5  137
2016-04-02 03:56 DK7FC     0.475682 -26 0 JN49ik 1  827
2016-04-02 04:42 WG2XJM  0.475761 -28 0 EN91wr 5  5732
2016-04-02 05:10 WG2XJM  0.475761 -29 0 EN91wr 5  5732

Not band with the takeoff in that direction!

Worcestershire Beacon

Monday, March 28, 2016

Upgrading the K3S for 475kHz

Having had the initial try of the K3S on 475kHz here It was time to properly implement the low frequency bands on the K3S. The first step was to convert both KBPF3 to KBPF3A (one on the main RX one on the SUBRX). It is a simple process requiring the removal of 2 inductors from the board and adding 3 capacitors in parallel with existing capacitors. To make it look neater I actually replaced the existing capacitors. While the KRX3 was open I also added the electrolytic capacitor specified across the 9V rail. The whole process took 30 minutes

While the box was open I also added the K3EXREF 10MHz lock board and the K144XV (with K144RFLK)

I hooked up the RX antenna port to the PA0RDT active antenna in the loft and was pleased to see some DX:-

 2016-03-28 00:04  G0MRF  0.475770  -13  0  IO91tk  5
 151  300 
 2016-03-28 00:00  DK7FC  0.475682  -20  0  JN49ik  1 827  295 
 2016-03-27 23:50  DH5RAE  0.475755  -28  0  JN68qv  0.5   1161  294 
 2016-03-27 23:16  PA3ABK/2  0.475785  -24  0  JO21it  0.5
 481  277 
 2016-03-27 23:14  F1AFJ  0.475703  -27  0  JN06ht  1
 625  341 
 2016-03-27 22:26  DJ0ABR  0.475665  -30  0  JN68nt  0.2  1148  294

Friday, March 11, 2016

Initial 475kHz use of the K3S

The one big improvement in the K3S, mainly due to the new synthesiser, is the ability to tune it down to 100kHz. The original K3 hardware only went down to 479kHz.  Using the K3S properly at these frequencies requires the installation of a KBPF3A. The original KBPF3 does not go down low enough in frequency, but can be easily modified.

As the filter board was not available we stuck a 40dB amplifier between the low 80m dipole and the RX Ant input, to make up for the loss in the normal K3S 1.5MHz highpass filter. The results on WSPR using the K3S internal soundcard were impressive:-

Date                    Call         SNR   Drift Grid             dbm   km
 2016-03-09 04:56 WH2XND -21      0 DM33xt      +43 1431
 2016-03-09 04:52 WH2XGP -25      0 DN07dg      +40 2499
 2016-03-09 04:50 WG2XIQ       +10      0 EM12mp     +37 60
 2016-03-09 04:48 WG2XXM +0      0 EM15lj      +37 258
 2016-03-09 04:44 WD2XSH/15 -23      1 EM34rt      +33 422

Monday, March 7, 2016

The new K3S arrives

Having had K3 for a while now I was interested to see the arrival of the "upgraded" model the K3S. While it is possible to buy the modules to upgrade a K3 to a K3S having done the calculations it was cheaper to buy a K3S in kit form and transfer the "option" modules across.

The K3S/100 kit, with the new 100W FET PA module was ordered.

It all went together easily enough despite some issues with K3 photos/figures appearing in the K3S manual (eg Figure 91).  It powered up fine and the VCO passed self test, so time to hook up an antenna. Nothing could be heard despite putting the RX on the TX7EU pileup.  As a check an HP signal generator was hooked up to the antenna port. It couldn’t hear -50dBm. Neither could this level be heard through the rx in port or the Xverter port. The radio was dismantled, all connectors checked, EEinit done, no improvement.

Time for more coffee, during which an inspiration. When I put the subrx into the k3 I remembered I had to remove a link in the KRX3 back connector. (J64A) So I searched the K3S manual. It appeared not to need the link as it was not shown in "Figure 31. RF Board Partially Assembled." or on the photo of the main rf board on Page a-14  or on "Figure 94. Installing the KBPF3A Option Board." BUT I noticed a link still shown on the legend on the PCB and its removal is still shown in fig44 of E740126A installing the KRX3A subrx. "Nothing ventured nothing gained", so I stuck a resistor lead in  the W4 link and the K3S burst into life. Sensitivity returned and the K3S was back to full health. Perhaps someone should have checked that when the K3 manual was converted to a K3 it was correct.

The other issue was the top left screw holding the bezel to the font panel would not bind. Close examination revealed that there was insufficient threading in the hole. After talking to Elecraft Support they shipped a replacement front panel, which arrived three days later and resolved the issue.

Saturday, February 13, 2016

Replacing the USB Connector on a Nexus 7 (2013 version)

Getting the charging cable to actually charge my Nexus 7 (2013 model) has been becoming Increasingly difficult. Having to balance the unit on a coffee jar and hang a weight off the USB connector at exactly the right point was a challenge. Searching the Internet I am not the only one to experience this issue. The recommended solution was to change the connector, as it becomes sloppy over time. I managed to find a connector for 1.49 off Ebay. Note the connector on the 2013 version is very different from the 2012 Version.

Guided by a Utube video I managed to get the Tablet apart, at a cost of broken finger nails, revealing the Innards..

The USB connector is on the lower edge. To remove the connector, first, using a sharp scalpel cut the 5 pins sticking out the back of the connector. If you do not,  you run the risk of lifting the tracks in further activities, The four lugs can then be desoldered and the connector removed. It is then a simple task to solder the new connector in place using a fine tipped soldering iron and thin solder. 

The Tablet can then be tested for correct operation before re attaching the cover. Mine charged fine and still produced video. Task completed

Tuesday, January 26, 2016

BARTG RTTY Sprint 2016

Having missed the ARRL RTTY contest earlier I was looking forward to a RTTY contest. The next one was the BARTG Spring Sprint.  The contest times are very civilised; noon start on Saturday, noon finish on Sunday (none of this 2am start of the BARTG March RTTY contest!!). Being a Sprint the contest exchange omits a report, only serial numbers are exchanged.

Looking in the loft I found the two Atom DG945CLF2 computers we last used in RTTY contests which ran Writelog under WinXP. Having now converted to N1MM software under Windows 7 a new computer with a more powerful processor and more memory was needed. I had built a media center in the USA using a DG41MJ motherboard. The case was also tall enough to acommodate the Delta D44 high performance stereo soundcard. Windows 7 32 bit  was installed with N1MM+ and the D44 drivers located. A stereo sound card is needed as the K3 supplies audio from the main receiver on the stereo left channel and audio on the stereo right channel from the sub receiver allowing two instances of MMTTY to be used to decode both frequencies. As usual FSK modulation was used.

The K3, KPA500 and KAT500 were assembled along with the newly established computer. The antennas were a good match so the KAT500 was not needed to match the antenna, but it does provide an easy way of automatically switching between the beam for 20/15/10, the 40m dipole and the 80m dipole.

The only issue experienced was that N1MM would go away and not allow anything to be done for periods up to two minutes,but would complain "K3 not responding" when it did come back and then work normally. This happened a dozen times on the Saturday evening, losing some QSOS. Changes were made, changing K3, closing N1MM windows, ferrite chokes, running without the amplifier but nothing changed, The same issue was also experienced with N1MM and a different K3 on a 432MHz afs a year ago which was never solved.   Then I remembered a similar issue with the TS950 and N1MM, The solution to this was to lower the polling rate in N1MM to 50%. This was tried with the K3 and the issue never happened again.

Conditions were poor for the contest and only 756 QSOs were had. All 6 continents were had for multipliers. At times it was slow that Practical wireless and the CDXC Newsletter were read!