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