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. 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 https://github.com/g0orx/pihpsdr  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

VSWR Plot

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 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 anglians / nactons on 4/2m and 8W from the K3 on 6m. On all bands it produces over 200W


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. Not surprisingly they say "STM"!

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