VE7BPO's Junk Box
This web page contains ideas, photographs, links and
potentially upcoming web site additions. The schematics on this page may contain
bugs.
Mouse over the images on the left to view a full size version.
RF attenuation has never been studied at VE7BPO. Shown in the photo are a couple of commercial 50 ohms step attenuators. Attenuation will be explored on the second installment of the RF workbench series. This is a critical tool.
First ever 50.0 MHz crystal oscillator. This is for the case study on the upcoming RF workbench page. There is enough material for 2 related web pages. The first RF Workbench page was published Feb 18.
Studying attenuation networks and filter theory.
The prototype popcorn variable attenuator. This was the first one built. It works well and analysis indicates a reasonably good input/ output match @50 ohms. Variation with the pot is >=20 dB. A shielded "keeper" version with an additional DPDT switched network was developed and is shown below. This was a contribution and I am very grateful to have received it. For the upcoming RF Workbench 2 installment.
Feb 27, 2010. Serebriakova Attenuator. This is my formal bench version. This Russian design is a contribution and is both fabulous and versatile. I envision that it will be used for multiple applications in experimenter circuits. My personal version has a switchable 4 or 10 dB pad on the front end and turning the pot from CCW to CW yields a variation of almost 23 dB at 50 ohms@ 14 MHz. The match is good. This thing is crazy cool. классно!
The schematic of a spectrum analyzer calibrator (W7ZOI design). It is rich in harmonics for analysis. To calibrate the output power to -27 dBm, the output was low-pass filtered and measured with a 50 ohm terminated oscilloscope. The trimmer resistor adjusts to get the required AC voltage. I am devoting all of Feb-March to learning more about RF measurement and building simple gear to do this. This will pave the way for exciting future projects.
Inside the 5 MHz Spectrum Analyzer calibration oscillator shown above. The power jack is connected via a rectifier diode to prevent a reverse polarity power supply mistake.
Not much can keep us off the QRP workbench; well Team Canada in the Olympic hockey finals does! Its our national sport.
An email question asked several times over the years is "what is the output of a diode ring mixer supposed to look like?" A new web page addition addresses this question and also points out that how invaluable a spectrum analyzer is for experimenters.
New receiver on the bench during final testing. It was the culmination of over 5 weeks of experimentation. This was the most intensive receiver development I have every performed. About 25 dollars worth of parts were consumed, but it was worth it.
An upcoming addition to the 2010 Hobbyist Page. *Improved March 6* This oscillator will work all the way up past 150 MHz. A number of tank coils and capacitors were tried. Although the schematic is built for 1 freq, by placing switchable series inductors and capacitors plus a big variable capacitor, this VFO will tune across a wide range. This type of oscillator is used for stuff like antenna analyzers. I measured greatest stability with high L to C ratios.
The breadboard of the above wide range oscillator. If you build one and it does not oscillate, you are really having a bad day! Mine just wanted to oscillate with pretty much any reasonable capacitor and inductor values. This is a fun circuit which begs for further experimentation.
A project from the RF Workbench Page 1 web page. This 50 ohm, 3 port device is used to sample the RF from a power amplifier and then examine it with a device such as a spectrum analyzer, power meter, receiver with an attenuator, or a 50 Ohm terminated oscilloscope. One use might be to look at transmitter's spectral purity with a spectrum analyzer. The output is 20 dB down and helps alleviate the need for a power resistor type 50 ohm attenuator.
Measuring insertion loss of filters, attenuator pads or the gain of an amplifier is explored in an upcoming feature.
The insertion loss (IL) of a low-pass filter is measured. This is a great filter. Others I measured had an IL of 0.36 to 0.69 dB. Some low-pass filters can have as high as 2 dB insertion loss. There are techniques to lower the IL and Wes, W7ZOI, has given me some hints. I am a total fan of his peaked low-pass filter designs.
Here is our server crew at the "pops.net command center". We have not met these kittens and look forward to spending time with them while on vacation in the U.S.A. this summer.
On the bench Feb 14: An 8 MHz Hartley local oscillator. The plan is to measure the voltage before and after inserting a sturdy low pass filter. It was pointed out to me that power calculations made from peak-peak voltages are for sine waves and not grungy signals with lots of harmonic energy. Some measurements and a strategy were developed.
The schematic of the 8 MHz Hartley local oscillator shown above. It was used to drive an amp into distortion. The effects of this distortion on power calculations will be shown and discussed.
My shop is very small and serves many functions. My wife came up with the idea for storing the common hookup wires and 50 Ohm patch cords used in day-to-day experiments; magnetic hooks on the upright freezer. These were purchased for a few dollars at a surplus store and hold well. In the bag is a small collection of SMA connector patch cords.
A version of the G3UUR crystal parameter checker. A new applet (G) that goes with it is now on the QRP tools page in beta version. The schematic may be found in many places including EMRFD Figure 3.35 See Errata and on this pdf. A supplemental web page to support this JavaScript applet was completed Jan 21. Link. This math is unpleasant, so I am hopeful the applet will address this problem. Надеюсь, что так!
Some of the 50 ohm modules recently built for the QRP workbench. Their greatest virtues include easy connection, good shielding and that they will last forever.
My call sign in Morse code
