- Population: 4,428,247
- Cases: 10,843
- Deaths: 196
- Percentage of deaths: 196 * 100 / 4428247 = 0.004%
Saturday, August 1, 2020
Friday, July 24, 2020
Tinker, Tailor, Soldier, SailorI like to tinker with old fashioned thermionic valve circuitry - tubes, for the 'Merrykins. It is strangely crude and simple and they make a friendly orange glow in the evening. However, powering the things is hard, due to the high voltages that are required to overcome the vacuum.
Heater Current Supply
Heater Current = 300 mA
Mains: 220 VAC at 50 Hz
Vdrop = 220 V - 12.6 V = 207.4 V RMS
Capacitor impedance = 1 / 2 x Pi x f x C
Z = 1 / 2 x 22 / 7 x 50 x 4.7 x 10^-6 = 677 Ohm imaginary
217.4 V / 677 Ohm = 321 mA
220 V Supply:
207.4 V / 677 Ohm = 306 mA
Safety Capacitors, 4.7uF, 10%, 350Vac, LS, 37.5mm
High Tension Supply
Bridge rectifier Vht = 1.414 x 220 V = 311 VDC
Mains: 230 VAC @ 50 Hz
Bridge rectifier Vht = 1.414 x 230 V = 325 VDC
Mains: 240 VAC @ 50 Hz
Bridge rectifier Vht = 1.414 x 240 V = 339 VDC
Diode, 1000V, 1A: 1N4007 (1 off or 4 off)
Protection CircuitryResettable fuse: 576-600R150-RAR
Voltage: 350 V maximum
Current 300 mA
Gas arrestors: From each mains wire to ground
Gas arrestor: 652-2045-40-BT1LF
Spark over: 400 V
Common mode choke: 10 to 20 turns, double wound
Toroidal core: 80-ESD-R-10E
Size: 10 mm OD, 5 mm ID, 5mm height
Monday, July 20, 2020
Sunday, July 19, 2020
A Formal Bow Tie EventI have made a few PCB antennas and the Yagis worked well, but they were very narrow band. So I tried to improve that by making the elements conical - or in this case, since it is 2D PCB antenna, triangular.
Monday, July 13, 2020
I needed a little clamp, but we were in Covid19 lock down. So I made one. No transistors, no batteries, no thermionic valves, no flashing neon bulbs!
There are many complicated ways to make a bar clamp, but I prefer the simple way. A picture is worth a thousand words:
It can't be simpler:
- One 6 mm dowel rod
- One 6 x 80 mm bolt
- One 1" nail
- Ten popsicle sticks
Yup - ten popcicle sticks glued together, made a small piece of plywood, that I could cut up for the clamp jaws. You can use the exact same method to make a big bar clamp. You don't need a super long lead screw, just a long bolt and a whole lot of little holes to adjust the other end of the clamp. Scale it up as required for size and strength.
How do I keep the movable jaw in place? Some funny putty (Press Stick) in a hole. It churns around in there and keeps the block from falling off the end of the bolt - a little piece of rubber will also do. The best way would be to file a ring in the end of the bolt, cut a washer in two and glue that into the block, but that is a lot of hassle - another day - do, do that on a big clamp.
Tuesday, May 26, 2020
On a Log-Periodic, all the elements are driven, but each dipole is reversed by 180 degrees. To make it on a single sided PCB, will require some links to wire up the dipoles. I added a BNC connector and thin equilength coax to the feed points of the antennas.
The important thing in radios is not the signal strength, but rather the Signal to Noise Ratio (SNR). A directional antenna reduces multipath reflections and noise from the surroundings and improves the SNR, so that a radio will perform much better with a directional antenna, compared to a simple omni-directional dipole.
Highest frequency f = 5200 MHz
Diameter of the shortest element ⌀ = 3 mm
Optimal relative spacing σo = 0.168
Number of elements ⌊N⌉ = 5
dipole l1 = 0.036 m
Sum of all dipole lengths lo = 0.146 m Distances between the element centres and their position along the boom:
d1,2 = 0.004 m, i.e. l2 @ 0.004 m
Boom length L = 0.012 m
Length of the terminating stub l_Zterm = 0.009 m
Bear in mind that the permittivity of FR4 (Fire Rating 4, glass and epoxy PCB) is about 4.3 and because the copper is in air on one side, the effective permittivity is less, about 3.3 - this conspires to make your antenna operate at about 20% lower frequency than the above (air dielectric) calculator indicates.
Version 1: Single Sided PCB
An antenna this complex, really should be built on double sided board, for best performance, but I managed to get the prototype together with 22 SWG hookup wire and RG316.
If you look closely, you can see the hookup wire links under the coax.
Considering how it was built, this is not too bad. It needs a balun to clean up the VSWR ripples.
Version 2: Single Sided PCB with J Balun for a Coaxial Cable
This test unit is a single sided board design, which requires wire links and there is no way to make microstriplines, since there is no ground plane, so eventually, there are multiple reasons to go double sided.
The graphs above show that the cable match is remarkably much better at the antennas. Next, I have to improve the power combiner/splitter match at the connector with a tapered microstrip line to improve the VSWR.
- Taper length: 18 mm
- Epsilon: 3.7 - FR4 glass-epoxy PCB
- Height: 1.5 mm - Standard double sided PCB
- 50 Ohm Width: 3 mm
- 100 Ohm Width: 0.8 mm
Target Frequency Band: 4.5 to 5.0 GHz
Design target for single sided FR2 PCB: +20% = 5.4 to 6.0 GHz
Widened design BW for parasitics: 5.0 to 6.5 GHz
LPDA — https://hamwaves.com/lpda/ — v20180914
LPDA design 2020-07-16 14:11
Lowest frequency f₁ = 5000 MHz
Highest frequency f = 6500 MHz
Diameter of the shortest element ⌀ = 1 mm
Characteristic input impedance Zc_in = 50 Ω
Taper τ = 0.880
Optimal relative spacing σₒ = 0.163
Chosen relative spacing σ = 0.060
Number of elements ⌊N⌉ = 5
Dipole element lengths:
dipole ℓ₁ = 0.030 m
dipole ℓ₂ = 0.026 m
dipole ℓ₃ = 0.023 m
dipole ℓ₄ = 0.020 m
dipole ℓ₅ = 0.018 m
Sum of all dipole lengths ℓₒ = 0.118 m
Distances between the element centres
and their position along the boom:
d₁,₂ = 0.004 m, i.e. ℓ₂ @ 0.004 m
d₂,₃ = 0.003 m, i.e. ℓ₃ @ 0.007 m
d₃,₄ = 0.003 m, i.e. ℓ₄ @ 0.010 m
d₄,₅ = 0.002 m, i.e. ℓ₅ @ 0.012 m
Boom length L = 0.012 m
Length of the terminating stub ℓ_Zterm = 0.007 m
Required characteristic impedance of the feeder
connecting the elements Zc_feed = 144.7 Ω
Now build it on FR2 and see whether it is anywhere near the desired band…
Thursday, April 9, 2020
To avoid this melt-down problem, military manpack radios are usually built with power transistors on the front end - the same ones used in the power amplifier. Since power transistors are expensive, commercial radios are usually not so rugged.
If your transmitter operates at +30 dBm (1 Watt) and the receiver has a sensitivity of -90 dBm (1 nano Watt), then to work properly, you need a path loss of 80 to 90 dB, to bring the transmit signal down to a safe level of about -60 dBm.
You can then hook the two radios back to back, with coaxial cables through the 90 dB attenuator, without risk of blowing anything up.
One trick, is to hook both radios to 50 Ohm dummy loads. They will then usually still work over the air for a few meters in a lab, due to leakage signals. A wireless connection like this can be handy for software tests, since you don't need to run a cable over the table/floor, but it is not repeatable for accurate RF tests.
Therefore, every radio shack needs one or two attenuators and dummy loads. If you go and look at the prices of these things on Pasternack, or Everything RF, you will see that they can be horribly expensive. You may be tempted to build one, but building a good one from little SMD coils and capacitors that will work at microwave frequencies, is difficult. Well, maybe not...
The above picture shows my 90 dB attenuator, made from three 30 dB attenuator pads, that one can buy on AliExpress Bokon Store for about $4 each, or from Everything RF for a few bucks more. So you can 'crook' and not actually build a T or Pi circuit - buy it as a little module and save yourself a whole lot of hassle and money.
Just solder three in series, add two connectors and an aluminium box for shielding and heat dissipation and Bob's Your Uncle? No, not exactly...
To get - 90 dB attenuation is very difficult in practice, due to leakage from the input to the output, inside the box. My first attempt came in at about -46 dB attention. I eventually got it up to about -60 dB, with careful routing of the little coaxial cables and some copper tape inside the box.
To Measure, is to Know (sorta kinda):
When I plug two RG58U cables into my little network analyzer and leave the ends open, it measures -80 dB. So with the cables I got, I cannot measure -90 dB. I would have to get double/triple screened coaxial cables to really know what the attenuation of this little box is, since what I measure, is the attenuator and cable leakage in parallel.
To actually measure this attenuator, I would need to build two and hook them up in parallel, then measure, so that I measure a lower value more within the capabilities of my test setup.
I have in the past made quite a few crude dummy loads from 50 Ohm 10 Watt wire-wound resistors soldered to a BNC/TNC connector. Some radios are OK with that, but some may not like it, since a wire-wound resistor is very inductive.
You can also get 50 Ohm thick film resistors that look much the same as the attenuator pads, to make accurate dummy loads that are not inductive. Screw one inside a little box with one connector and there you are. If it is an open construction like this, then they will radiate a little, which is sometimes useful. The small piece of scrap PCB acts as a heat sink - good for a few Watts.
Grey anti-static bags work as a RF attenuator. The bag data sheet shows that it is a multi-layer composite with a thin transparent aluminium layer inside:
My measurements showed a 15 dB attenuation at 5 GHz when I put a bag over an antenna. This is useful when two radios under test are too close together and you need to suppress the signal a bit, without changing the wiring to install/remove an inline attenuator.
It is Time, Gentlemen