Posts Tagged ‘homebrew’
Do You Have ‘It’ ?
May 31st, 2015 | 
Author: As a kid, I always loved to take things apart to see how they worked. Although building wasn't the driving-force to get my ticket as a teenager, I soon became an ardent homebrewer and have loved building radio gear all of my life. When in high school my favorite classes, and teachers, were the shop courses which led me to become a Tech-Ed teacher at 21 years of age. I think it all started with an early case of the ' knack'.
49’er & Fake Transistors
A recent posting to Yahoo's 'GQRP' reflector spurred discussion of the growing number of fake transistors being seen on e-bay. A builder enquired about the low efficiency noted in his recently built Chinese '49er' kit.I recently bought one of the Chinese Forty-9er transceiver kits off ebay and on receive it works well. It certainly transmits, but the power is down to 800mW and the driver transistor is getting very hot. I'm not expecting a lot of power from it, but power claims are 1.8W to 3W. I'm more concerned about the hot driver transistor. The following link shows the circuit diagram.
http://www.ebay.com/itm/DIY-kits-Frog-Sounds-HAM-Radio-QRP1-8W-CW-Transceiver-Receiver-7-023MHz-/121507448525
I've checked for spurious oscillation (a problem I've had before), but can find nothing. Does anyone have any ideas for why the transistor is getting hot?
It was suggested that the transistor in the PA may not be up to specs and even be a 'fake' as these types are commonly noted on e-bay, selling for prices that are too good to be true.
The problem was eventually sorted out by exchanging transistors:
Firstly, thanks for all your help. Initially, I replaced the Chinese PA transistor with a BD139 and that increased power output to 1.2W and reduced the heating of the driver. Key down and it took perhaps 20s to get "finger hot", rather than 10s. Tonight I changed the driver transistor to a 2N3904 as used in the original Forty-9er and the driver heating seems to have gone away. A small heatsink on the PA transistor allows it to run at 1.4W output for 30s of keydown without any drop in power or the heatsink getting any more than warm.
Thanks for all your help and I hope this helps someone else.
A search of Youtube videos shows several builders that have split some of the RF devices open in order to compare die sizes of suspected fakes with the real thing:
Earl Andrews, VE3GTC, has gone to considerable effort to test and compare many of his transistor purchases and indicates that there are a lot of devices coming out of China that are outright fakes and have no hope of meeting the specs that you might expect. His interesting website has a lot of details about testing as well as a very comprehensive 'for sale' list of reliable devices. Earl also suggests using caution when buying e-bay Chinese electrolytics as his measurements of ESR values indicate that many do not pass specs.
If you have purchased fakes or have found a Chinese source of the real thing, please let us know ... I'm sure there are plenty of dealers selling the real thing out there.
Stealthy Roof Mast
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| courtesy: https://openclipart.org/ |
This time it's his stealthy mast to support some small VHF utility antennas. If you're interested in a simple stealthy mast for the roof-top, you may find some worthwhile hints here. His system would make a very nice stealthy support for a PAØRDT mini-whip which would put your antenna well above the house and its associated noise fields ... have a look.
Inexpensive Kit From China
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| courtesy: http://www.banggood.com/ |
A recent posting to the GQRP Yahoo Group brought my attention to another inexpensive offering from China. This time it's Bangood's complete "Pixie" type 40m QRP transceiver for the incredible sum of $4.16 (U.S.)! The price includes all components, a nicely silk-screened PCB and free shipping. One really wonders how it is possible to make any profit with such an offering but it obviously is. However, all may not be what it seems. One purchaser, IK1ZYW (Paolo) who built the kit, described his findings in a recent blog posting of his building experience.
In spite of the problems noted above (with some now corrected), the kit still seems a bargain, if one takes the necessary care with construction.
Playing with QRP can often provide ham radio's best "fun for the money" as DX- capable transmitters can often be built for just a few dollars. I vividly recall the fun I had one winter while pursuing the first-ever Tuna Tin W.A.S. endeavour on 7040kHz.
I made many new friends on 7040 that winter and every weekend many of them would listen-in or call to see how my progress was going. The highlight of the adventure was late one Saturday night when I had three New England stations all answer the same CQ ... what amazing fun for a handful of parts at less than $10 ... not including the cost of a can of Tuna!
The little Pixie kit offered above has a power level fully capable of W.A.S. on 40m and with the decrease in solar conditions, 40m will just keep improving. If you purchase and build one of these kits, please let us know how your experience went. The 'interesting' construction notes may be found here.
Some PMR fun
One is a Tait T535 2-Channel Mobile PMR which can be converted to amateur 2m operation relatively easily. Details are available on the internet including David Pye's website. I intend to use this unit to set up a permanent APRS internet gateway/digipeater.
While walking around with the Tait I attracted the attention of another seller who had some PYE MX294 units for sale. One was already converted to work on the 25kHz spaced simplex and repeater channels with CTCSS. The other was only partly converted and they came with a box full of spare boards and mounting plates and an original microphone and speaker. I wasn't really looking for any more units but seemed a bargain for £20.
The PYE MX294 was indeed converted and seemed to work fine on the simplex channels, and while it was receiving and transmitting on the repeater channels it wasn't transmitting the CTCSS sub-tone. With some sage information from Ian MW0IAN on twitter it was a simple issue to solve, using the oscilloscope I confirmed the tone was being generated it was the pot controlling the level that was set too low.
The Tait is proving a little more involved. It has a diode matrix board to set the Tx/Rx frequencies which has been set incorrectly. It also had a CTCSS board that was hard-wired in rather than socketed which I have now removed. The information of which diodes to link/unlink is freely available, however I decided to create a small windows utility to simplify the calculation. This is available for download from my website, it is supplied as is and with no warranty.
There are a number of modifications to add multi-channel to this radio by the use of eproms, but I am considering devising an Arduino solution to allow setting of frequencies and possibly selection of CTCSS.
First 475 kHz WSPR decoding
Tonight I made the first successful decoding of WSPR on the 630 m band. What inspired me was all the talk on the Elecraft reflector on the new synthesizer which in addition to having less phase noise, also allows the K3 to go below 500 kHz. I don’t have that synthesizer, but the discussion reminded me of the low frequency converter I built many years ago. It converts 0-1 MHz to 14-15 MHz. Using the KXV3 transverter interface of the K3 it was easy to interface and get up and running.
The first signals I decoded are shown in the water fall above, and their origin in Germany and the Netherlands is shown in the next figure.
According to WSPRnet, PA0A’s 2 Watt transmitter is 784 km away from me, and DK7FC’s 1 Watt is 1164 km away.
The converter is based on a 74HC4053 switch used as a mixer with a 74HC04 for a 14 MHz oscillator. It is based on SM6LKM’s design, but with a different oscillator frequency and a simplified output filter. It is one of many small projects that I have built in Altoids tins. The antenna used was my trusty old 80 meter horizontal loop with a 4:1 Elecraft balun.
Perhaps the next step is to finish the 475 kHz filter of my Ultimate 3 WSPR transmitter and see if others can receive me? That is going to be more of a challenge antenna-wise.
First 475 kHz WSPR decoding
Tonight I made the first successful decoding of WSPR on the 630 m band. What inspired me was all the talk on the Elecraft reflector on the new synthesizer which in addition to having less phase noise, also allows the K3 to go below 500 kHz. I don’t have that synthesizer, but the discussion reminded me of the low frequency converter I built many years ago. It converts 0-1 MHz to 14-15 MHz. Using the KXV3 transverter interface of the K3 it was easy to interface and get up and running.
The first signals I decoded are shown in the water fall above, and their origin in Germany and the Netherlands is shown in the next figure.
According to WSPRnet, PA0A’s 2 Watt transmitter is 784 km away from me, and DK7FC’s 1 Watt is 1164 km away.
The converter is quite simple and is based on a 74HC4053 switch used as a mixer with a 74HC04 for a 14 MHz oscillator. It is the design of SM6LKM, but with a different oscillator frequency and a simplified output filter compared to his. It is one of many small projects that I have built in Altoids tins.
The antenna used was my trusty old 80 meter horizontal loop which has been the main work horse for making my 8-band DXCC (more than 100 countries on all bands 3.5 – 28 MHz) possible. It is fed with ladderline into a 4:1 Elecraft balun in the shack.
Perhaps the next step is to finish the 475 kHz filter of my Ultimate 3 WSPR transmitter and see if others can receive me? That is going to be more of a challenge antenna-wise.
