I picked up my old TNC2 packet controller and dusted it off today. After finding an old Hayes modem cable I was able to wire this dude up to my laptop. About a million years ago, I registered a version of UIView32 which is a nice little APRS mapping package.
Of course there were no maps of the Western Washington area available for the software, but there is a nice feature where you can drag/drop a map bitmap onto the software and then define the lat/lon details for either the upper/left, lower/right corners of the map or by clicking on two points on the map and defining the lat/lon for those points. I took a screen shot of a google map and defined two points. Not totally precise, but close enough for giggles. Here is a peek of the map after it has had a little while to listen on 144.39 Mhz to the APRS traffic.
I have an old Alinco dual-band rig that I inherited from my dad (W7QJC) R.I.P. that I might press into service for packet radio playing around. Gotta get the transmit portion working next. Just need to set some jumpers to match the microphone wiring and plug it in.
This morning I had some fun with my Arrow antenna and an old Yaesu 2 metre hand-held transceiver. I generally track a hand-ful of Ham Radio satellites, one of which was recently launched from the International Space Station (ISS).
This morning about 10:20 Pacific Time, we had a nearly overhead pass of the satellite giving me about 10 minutes of time to to track the bird and listen to its beacons.
At the appropriate hour (and minute) I was the image of tin-foil-hat-geekdom standing out in my yard with a pair of headphones on listening to a handheld radio whilst pointing a very strange contraption (the Arrow Antenna) skyward. I live on some acreage, so I don't have neighbors withing spitting distance, but nevertheless, it was a bit of a "moment" for me wondering if anyone watching would think the old man has taken leave of his senses...
But, the sights being whatever they were, I was having fun... I had a great copy on the bird, but didn't happen to plan ahead sufficiently to enable me to record the pass. Even with the tall trees around, I had no problem copying the pass and sent off for my reception report giving two of the (english) passwords copied during the pass as proof of reception.
If you have not tried to copy ArisSat1 yet, it is very easy even with a handheld receiver and a modest vertical antenna.
The next round for me will be to try and catch some of the telemetry. I will have to look at the satellite status page to see if the transponder is still functional, but a contact or two over the bird would be fun.
Reading the brainwagon.org blog, I came across today an 8080 emulator that is implemented (of all things) in JavaScript. I can load it up in a web browser and load a working CP/M OS image and found myself soon playing Zork1.
Cracks me up to think about running an emulation of hardware that I wrote code on for a living, running a predecessor to MSDOS operating system and playing an adventure game all written in an emulated language embedded in my web browser...
Geeze, I am getting old... :\
After discussing with my buddy Eldon, I have decided not to use the voltage divider approach to power the filaments. They are all wired in parallel and the risk from one of them opening up and thereby taking out the entire set of tubes is too great, not to mention the royal pain in the tush finding a 1.15 ohm 15 watt resistor will be. I decided to order a 2.5 volt 6 amp transformer from Mouser for $13 today and will use it to power the tubes. The other option would have been to rewire them all in series and use a voltage divider to come up with 7.5 volts from a 12 volt source. At least if a filament opens up we power everything down, plus the voltage divider would be easier to construct without having to locate 15 watt resistors.
I love a few select old pieces of equipment, but powering them can be a pain in the empennage. I have a couple sources for the B+ 135 volt supply, so we should be good to go once the transformer arrives.
Meanwhile, I am on the lookout for an old National "doghouse" power supply for the SW-3.
A while back, I posted a note about having found an old 1930's National SW-3 receiver. The rig came without a power supply. I need to have 2.5 volts at about 3 amps to power the tube filaments. I have a 6.3 volt supply at 4 amps, but need to bring this down to 2.5 volts at 3 amps. So, I thought I would just use a voltage divider.
o--------------------+-----------------o +6.3V
|
R1 3.8 volts across R1
|
+-----------------o +2.5V
|
R2 Load = 3 amp @ 2.5 volt
|
o--------------------+-----------------o 0V
So, how to design a simple two resistor divider? Assuming that there is no load current:
Vout = Vin * R2 / (R1+R2)
The problem with this is that our load DOES draw current (about 3 amps) and therefore this will not work because the load can be considered another resistance in parallel with R2.
The 10 percent rule is a standard method for selecting R1 and R2 that takes into account the load and minimizes unnecessary power losses in the divider.
So, the first thing to do is select R2 so that I2 is 10 percent of the desired load current. This resistance and current is called the bleeder resistance and bleeder current. In this example, the bleeder current is:
Ibleed = I2 = 0.1 * 3 A = 0.3 A = 300 mA
Using Ohm's law to calculate the bleeder resistance:
Rbleed = R2 = 2.5V /0.3 A = 8.3333 ohm
Now, we need to select R1 so that the output is maintained at 2.5V. To do this, we simply calculate the total current through the resistor and use Ohm's law:
I1 = I2 + Iload = 0.3 A + 3 A = 3.3 A
R1 = (6.3 V - 2.5 V) / 3.3 A = 1.1515 ohm
Now considering standard resistor tolerances and value, this would indicate the need for R1 = 8.1 ohm for a 5% resistor and R2 = 1.15 ohm.
In terms of power ratings:
P1 = V1^2 / R1 = 3.8^2 / 1.15 = 12.55 W
P2 = V2^2 / R2 = 2.5^2 / 8.1 = 0.77 W
Did I do this right?
I am not sure what happened, but the first time I did this exercise, I (somehow) came up with R1 = 7.5 ohm 3 watt and R2 = 5.6 ohm 5 watt...
More coffee...
I know it has been forever since I started the Arduino beacon project and while the functionality is 90% or better complete, the project has been on the shelf for a very long time. Between family illness, work issues and the like, ham radio has taken a bit of a holiday.
Today I drug out the beacon hardware and spent some time reviewing the software. I made sure I could still build the code and flash the device with the image. All is well in that department. I spent some time tidying things up a bit in the code and removing some edge case failures.
I have reduced the functionality of the software to three modes:
1. Signal Generator - General purpose, turn the dial, set the frequency mode.
2. WSPR beacon
3. QRSS beacon
There is also a real-time clock setting mode, but that is more of a utility.
The WSPR beacon has preprogrammed all defined WSPR frequencies from 500 kHz to 50 mHz. A single button push will cycle through all of the WSPR frequencies and sets the beacon to the centre of the band. From there, the rotary dial will allow adjustment down to 1 Hz.
The QRSS beacon transmits on whatever frequency is set on the dial. The beacon continually transmits until the operating mode is changed.
There are a few things to do yet to finish off version 1 of this project.
1. WSPR mode needs to allow adjustment of the TX percent value as well as the call sign and power level. Currently it requires recompiling the code to change these values. The TX percent value is not currently respected and the beacon currently transmits once and then enters IDLE mode until WSPR mode is reselected.
2. QRSS mode needs to allow changing the QRSS message without recompiling the code.
I think at this point the code could be declared V1 complete. A few lower priority changes might be the definition of V2.
1. The WSPR beacon should have a mode where it cycles through all 12 WSPR bands. The challenge here of course would be to create a 12 band antenna system from 500 kHz to 50 mHz.
2. Allowing finer control of the frequency with the rotary encoder. Currently the resolution is 1 Hz.
3. Automatic saving/restoring of all settable parameters in EEPROM.
I am going to try and get V1 completed by the time our QRP group meets this Wednesday. It will be a bit of a challenge, as I need to finish the packaging of the hardware, but will give it a go.
With my renewed interest in old-tyme radios, I have decided that I need to have a good adjustable lab bench power supply that will give me filament, B+ and C voltages appropriate for these old radios.
I have located a nice Heathkit supply that has 6.3 VAC at 4 amps for filaments, adjustable 0 - 400 VDC at 100 mA and 0 - negative 100 VDC.
For my SW-3 receiver, the filament voltage is too high, so I will have to build a voltage divider to bring that down to 2.5 volts. Just tested it out and everything is working perfectly.
After a couple years of looking, I have located a National SW-3 receiver that is in good shape.
It came with a couple sets of coils, a bandset coil set for 80 metres and an unknown coil set that was hand-wound by a previous owner as well as two sets of empty coil forms for my own hand-wound coils. Subsequently, I have obtained a bandset coil set for 160 metres.
I am now looking for a period power supply, preferably one of the National "Dog-House" power supplies.
My SW-3 is one of the earlier version 2 receivers. It has a pair of 58 valves (tubes) and a 50 valve (tube). The filaments are 2.5 volt and the B+ is anything upwards of 350 volts though the National power supplies typically supply around 135 volts. Meanwhile, I plan to locate a nice high voltage lab supply to be able to test this little beast out.
Wow, has it really been nearly three months since I updated this blog? Very sorry to be away so long. I have a couple of new short posts to get back into the blogging mindset.
My apologies for the long time between postings. I have been a bit preoccupied with my son's cancer treatments. I hope to be able to return to my electronics and ham radio pursuits soon.
