Monday, December 11, 2017

Making the K3 internal Transverter more External Transverter proof

Having suffered with the K144XV internal transverter's lack of useful output adjustment range, I finally decided to do something about it. The issue is that with the power control fully clockwise the 144 MHz output power is 9W. With the power control fully anticlockwise the output is 1W. This is the only band you cannot turn the output down to 0W!.  If you set the the IF level to -10dbm, fully anticlockwise is still 1W, as is every other setting of the knob.

The issue was raised with Elecraft over 3 years ago, but they said there was no software solution. They did point out that there is a drive pot in the module that could be adjusted to make the maximum level suit my transverter. After blowing up the pin diodes in my DB6NT transverters on more than one occasion, it was time to investigate.

Reference to the circuit of the K144XV revealed the pot was labelled R87

After removing the K3 top cover and the Transverter top cover, R87 was physically located between L3 and L4. It is shown in the following picture:-

Next a small hole was drilled to allow a trimming tool to adjust VR4 with the lid still on the transverter, as shown below:-

I set VR4 to give 1.2W with the drive level set in the menus to 0dBm. The adjustment range is similar, but now there is no risk of overdriving and destroying the transverter.

Another advantage of the new configuration is that the positive  voltage on transmit present on the XV connector centre pin is retained for transverter switching. Previously with an external attenuator the DC component was dissipated and an external Bias-T was needed to switch the Transverter.

Wednesday, October 11, 2017

1296MHz Trophy 2017

Having been to Dorstone two weeks previously for the UKAC with poor results to the North, I wondered whether it was conditions or if there was not just enough time to set up skeds on ON4KST. to work them.  Six hours of operation in the 1296MHz should provide an answer, especially as for the first time i could use the SCC M2I.

As there are no power classes in this contest the full 350W from the 4 x MRF286 amplifier could be deployed (as opposed to the 2 x mrf9060 in the UKAC) to the 44 ele Wimo. 48QSOS were made  with the best DX being DK2MN at 684km Some other noteable dx was PI4GN, PA0S, OT5A/P GD8EXI, GU6EFB and GI6ATZ. The only failure was with G4ALY who by the time i found him on CW my keying paddle springs had fallen apart. The only escapee on ON4KST was G8PNN, who admitted at the RSGB convention had been replying to M21 not M2I 

The conclusion of the operation was that with the extra time some of the weaker northern stations were workable, the site was alright

Things got so quiet towards the end i spent the last hour trying to receive the GB3ZZ DATV repeater. The 46km proved not possible (and having plotted the path on my return home I can see why!)

I also took along the 13cm system with the KX3 which although it could receive beacons produced no power, which turned out to be the KX3 not being able to produce sufficient voltage (~3.5V) on the antenna connector to switch the transverter to transmit.

Saturday, September 30, 2017

RSGB National Hamfest 2017

This years visit was made on Friday as usual. There was heavy rain as the outside area opened, so much so that the inside hall was opened early. A used Tonna 50MHz five element  yagi for £20 was purchased from the flea market with the intent of converting it to a lightweight 4m Yagi. Indoors a four section 20' swaged mast was finally bought (I thought about getting one last year!) from Moonraker

The usual big traders were in attendance, although some on a smaller scale than last year, for example Waters and Stanton. It was impossible to get near the QRPLABS stand as G0UPL had to queue of people placing orders. I have still to finally meet him after having previously had many transactions with him from Texas

The highlight of the trip was non transactional! A few months ago I assembled the BATC minituone receiver, but it failed to receive the DATV signal generated by the RPI, even though it passed self test so I put it aside. The BATC would be at Newark and I guessed would have real DATV signals, so I took the receiver along. Noel G8GTZ was only too pleased to try it out and it passed testing with flying colours. Now I can move onto assembling my Portsdown Transmitter modules

Monday, August 28, 2017

5760MHz UK Microwave contest August 2017

Having previously finished encapsulating my 6cm amplifier, I was eager to try for some QSOs. The UK microwave groups 5/10GHz activity contest on July 27, G4DDK had given me a 5Ghz patch antenna which would be easier to use than my 0.6m dish. I ended up packing the 5760 EME transverter, the amplifier , and the KX3. As it was a 12V system everything could be run from the car battery

As the local site at the tump at IO82UA had a good takeoff to many directions North through southwest, it made an ideal starting point; if anything didnt work I would be close to home to get it fixed

The first attempt was with GW3TKH/p operating from the Blorenge IO81LS. Signals were easily exchanged, but holding the antenna in one hand, writing the log entries and tuning the rig was quite tiring!Signals were also exchanged with GW4HQX/p at the same location

The path SW to GW3TKH/P
 The next attempt was with M0HNA/p in IO91GI. He had linearity issues so no SSB, so we tried NBFM. No problems in exchanging signals, and the best DX at 94km. I next tried with G4ODA. Signals could be seen on spectran in both directions, but not loud enough for a QSO.

The Path  SE to M0HNA/p

I wanted to try with G3XDY and G4JNT, but both were too busy setting up skeds on ON4KST. Hanging around was not possible as I needed to move to the other side of the malverns to work G3ZME/p in IO82QL before the contest ended. I left the Tump and went searching for a suitable location. I found a couple of locations but it is amazing how big the field hedges are on the west of the Malverns which precluded their use. I ended up again going to Ankerdine Hill IO82TF, where despite pointing through dense foliage a qso with G3ZME/P was completed, again handholding the patch antenna.  By this time G4JNT was free, but the Malverns caused a major path obstruction.

A very interesting trip out and some interesting points learnt for future operations

Sunday, August 13, 2017

432MHz UKAC August 2017

Time for the annual 432MHz UKAC outing, mainly to try out some new equipment locally before taking it further afield. The new all digital KR400 rotator needed testing, as did the recently rediscovered DEMI ex TV transponder amplifier. Both worked fine. Heavy rain delayed going to site, so only operated 2 hours. However 77 QSOS were made as G4NXO/P, best one being 390km into Paris. Equipment ran a K3S into DEMI Xverter, TV Transponder PA module running 100W into a 21 ele F9FT. The HA8ET mast head preamp was mounted at the base of the mast due to the length of feeder on the Yagi

Saturday, May 27, 2017

ADF4351 Signal generator revisited

My previous attempt at building a 35MHz to 4.4GHz signal generator here had been thwarted by  a fake chinese chip recorded  here. From consumer feedback it appeared that much less trouble was being had with the black ADF4351 chinese board with the 2x5 pin header. I also noticed that BATC were using one in their Portdsown DATV Transmitter. So I bought one from "alicehappy858" on ebay

It took 15 days to arrive, and ten minutes to rewire the header. One very important point to note is that the header pin marked "3.3V" is a 3.3V OUTPUT from  from the 3.3V onboard regulator, NOT a 3.3V INPUT.  5-9V needs to be applied through the tiny barrel connector on the edge of the board of the black version.

Having taken care of that issue I again used my modified F1CJN software published here , modified to use the Adafruit RGBLCD shield that I had. The unit locked all the way from 35MHz to 4.4GHz and the Frequency counter agreed. Success at last!

Friday, March 31, 2017

Homebrew PiHPSDR

Having seen the Apache-labs version of the PIHPSDR I wanted to customise it to fill my needs, so I needed to assemble my own

All the needed information , with the software,  is at John Melton's github site  The hardware shopping list includes. RaspberryPi 3, 7" Official Raspberry Pi LCD,  8 push buttons, 4 rotary encoders, case and power supply.

All the items were mounted in a 12x7x2" aluminium case obtained from Mouser, The display was held in place with plastic channel finishing strips from B&Q.

Front Panel View

Inner View
Initially I used a $30 rotary encoder that I got off ebay, but being designed for attaching to a motor it was a bit big to go in the box. I replaced it with an HP  HRPG-ASCA # 14F which cost $5 off ebay which fitted nicely into the box.

When first built, I used a 5V 3A regulator bolted to the Aluminium case. However this was dissipating around 8.3V at 2A and was too hot too touch. I tried a series of diodes, each with 0.6V drop on the regulator input, but that also got hot.  The regulator was replaced with a DC-DC switching converter from ebay which kept cool. The negative lead of the power supply, and the negative lead of the RPI were both grounded to the case to avoid negative lead voltage drop issues which caused RPI brownouts

I also included a USB soundcard in the box so i could listen to both audio channels when remote from the ANAN. The audio connections were extended to sockets mounted on the Aluminium box. Due to the close spacing of the USB ports on the RPI, and to allow plugging other items into them, the plastic case on the USB soundcard was removed.

The total cost of the homebrew PIHPSDR was around £120

Thursday, March 30, 2017

AQRP VIA Power Source Improvement

Running the VIA from the rechargeable Eneloop cells from the VIA was tolerable for a while, but the batteries had to be extracted from the battery holders in the unit every time a recharge was needed.

The VIA documents mentions using a "2600mAH power bank". These provide a regulated 5V output from a USB connector and can be charged from a phone charger with microUSB plug.  Ebay had them for 99 pence (shipped) so a couple were bought.

Testing them to power the VIA externally proved they would work fine. The BIG issue was that  power bank box was too big to squeeze into the VIA so the power bank contents would have to be extracted from the package. This was done but it was quickly discovered the controller boards are destroyed if 5V from a charger is applied without the battery connected. The LIPO cell still worked. Time to look for a more robust charger for my growing LIPO cell collection

Adafruit had a Powerboost 500 charger/booster which looked to be well suited. It also had the advantage that the VIA could be powered at the same time as the cell was being charged. One was obtained for $15 and squeezed into VIA with the LIPO cell, as shown below.

Controller  shown top Left, just above the LIPO cylindrical cell
The system powers the VIA for well over an hour, which is very acceptable. A hole was made in the case to allow the charged and charging LEDs to be viewed with the case lid on.

Tuesday, March 21, 2017

Austin QRP Club VIA Finally Built

I had seen the specifications for this Austin QRP Club Vector Impedance Analyser kit when it was first announced. It covered 1 to 150MHz or 8kHz to 1.17MHz (good for LF) and offered a range of different format results display on it's TFT Display; no need for a computer to drive this one!  I bought the kit from K5BCQ's web page about a year ago and recently decided it was time to build it. The microprocessor board is prebuilt, the TFT display is prebuilt, the only board which needed building is the RF board which also connects the other two boards together. The RF board took about 2 hours to build

The recommended enclosure was obtained; not cheap at around 20 pounds, but makes for a neat unit. I used an SMA connector for the antenna port.

Not surprisingly the software had been updated since I bought the kit, but it didnt take long to do the upgrade following the instructions provided.

Initially the unit was powered by six Eneloop AA cells mounted in the supplied battery holders connected via the regulator board supplied with the kit providing regulated 5V

The flash screen came up immediately and following the instructions in the manual a 2 MHz to 30 MHz open/short/load calibration was done. My Alpha-delta DXCC antenna was connected and the VSWR, Return Loss and even a smith chart plot were obtained


Return Loss

Smith Chart

It is possible to export the data to a computer and process it in any way you want. 
 Another useful display is the Alphanumeric display which shows the parameters as numbers. One use of this is to measure capacitors and inductors at RF Frequencies 
Alpha Display
Very impressed with the unit, especially as it cost under 100 pounds. Cannot wait until the transmission measurement add on becomes available

Sunday, January 22, 2017

Triband 6/4/2m Amplifier finally finished

Last Summer, browsing ebay, I found a Kalmus 172F wideband amplifier. "Kalmus broad band vhf power amp model 172F High gain 200 watts rf output <1w @ 50-100mhz <4w @ 144mHz, on the tin it does say 80-160Mhz but it does cover 50-70MHz, supply required 28 volts dc 14 amps" Looked interesting so I bought one

In the last few weeks finally got around to using it. I wanted it to be smaller than it's bigger 400W brothers so i managed to squeeze it into a 12x7x3" box. No room for low pass filters so they have to be plugged in externally. A PIC oversees the amplifier and displays status on a front panel 20x4 LCD.

The kalmus amplifier already has a bridged T input attenuator, so I increased it by 3dB so I can drive it with the 7W from the Anglian / Nacton XV on 4/2m and 8W from the K3 on 6m. On all bands it produces over 200W