|HK1NA (worked today) operating CQWW|
Some of the operating skills were amazing: PJ4X was working stations at a rate of one every 5 seconds. He spoke so crisply and quickly that by the time I'd called he'd already worked another station!
|HK1NA (worked today) operating CQWW|
|500kHz first JT9-2 signal received|
|XV1X QSL card|
|The wide graph display for JT9|
"I invite you to try a new digital mode called JT9, designed especially for making amateur QSOs at MF and LF. JT9 uses the structured messages introduced in 2003 for the JT65 mode, now widely used for EME and for QRP operations at HF. JT9 can operate at signal levels as low as -27 dB (in a 2500 Hz reference bandwidth), with one-minute timed transmissions. It also offers slower transmissions of 2, 5, 10 and 30 minutes duration, and the slowest mode can decode signals as weak as -40 dB. With one-minute transmissions, submode JT9-1 has a total bandwidth of just 15.6 Hz -- less than one-tenth the bandwidth of a JT65A signal. The other submodes are narrower still: a JT9-30 signal occupies about 0.4 Hz total bandwidth.
Note that these JT9 sensitivity levels are comparable to or better than those of WSPR, which uses simpler messages and is not intended for making 2-way QSOs. JT9 has much higher throughput and reliability than QRSS CW, including DFCW modes.
JT9 is implemented in an experimental version of WSJT called WSJT-X. Some further details can be found at http://www.physics.princeton.edu/pulsar/K1JT/WSJT-X_Quick_Start_Guide.pdf , and an early version of WSJT-X can be downloaded from
Please note: WSJT-X is in an early development stage. A number of improvements and enhancements are already in the works, and others will surely be added.
Your feedback will be much appreciated!
-- 73, Joe, K1JT"
|A photo of the Argonaut VI on the K4SWL website (linked)|
|CQ zones map|
|Over-the-horizon 481THz optical signal from G4HJW last winter|
|Homebase-10 antenna on the back of my house.|
|Unique 10m WSPR reports with 200mW and a halo today|
|The excellent conditions on HF today|
|Rev H 472/500kHz Transverter Schematic (click to enlarge)|
"A British firm based on Teesside says it's designed revolutionary new technology that can produce petrol using air and water. Air Fuel Synthesis in Stockton-on-Tees has produced five litres of petrol since August, but hopes to be in production by 2015 making synthetic fuel targeted at the motor sports sector. The company believes the technique could help solve energy supply problems and curb global warming."See http://www.bbc.co.uk/news/
|LA5VNA's version of the G3XBM 472/500kHz transverter|
|IC7100 - will there be a QRP version available in the USA and Europe?|
|K1IED who worked many QRP AM stations on 10m today|
|Earth-mode test results. Distance to "best DX" location 6km NW of TX|
|Much weaker signal copied at 4.4km SW today (nowhere near strong enough for QRSS3)|
|MF WSPR activity this evening|
|5W 8.978kHz QRSS3 earth-mode signal at 1.6km (STRONG)|
|G3ZJO's (very neat) version of my 472/500kHz transverter|
|QRSS3 signal at 1.6km using a 30t 80cm loop on RX|
|10wpm signal at 1.6km using a 30t 80cm loop on RX|
|SWL Roland's enhanced SM6LKM software VLF receiver|
|VLF Earth-mode Beacon Transmitter|
The current prediction for Sunspot Cycle 24 gives a smoothed sunspot number maximum of about 75 in the Fall of 2013. The smoothed sunspot number (for 2012/02) is already nearly 67 due to the strong peak in late 2011 so the official maximum will be at least this high. We are currently well over three years into Cycle 24. The current predicted and observed size makes this the smallest sunspot cycle since Cycle 14 which had a maximum of 64.2 in February of 1906.http://solarscience.msfc.nasa.gov/images/ssn_predict_l.gif
|Tim in one of his many appearances at Ronnie Scott's in London|
"Dear Roger, Andy, LF Group,
>> Four turns minimum for 137kHz 25 Watts. 60 or so for 9kHz
> Yes these values look quite practical ones.
...But now the inductance of the winding and AL value of the core do become important. (BTW, the value of 2000 is the relative permeability of the 3C90 material. The "inductance factor" AL, the "inductance per turn-squared", is a different number which depends on the shape and size of the core as well as the permeability.) AL for this core is given as 2690nH nominally. With a four turn winding, the resulting L is about 43uH, with a reactance of only 37ohms at 137k. In a 50 ohm circuit, this will cetainly mess things up a bit. As a general rule, you would probably like the reactance of the 50ohm winding to be at least 250ohms at the operating frequency. This requires an inductance of more than 290uH, so a winding of 11 turns minimum will be needed for a 50ohm impedance level.
This is a typical result when using a core that is much larger than what is required by power handling considerations - the number of turns needed to keep the flux down to an acceptable level becomes so small that the inductance becomes the deciding factor. It also obviously makes it tricky to match to low impedances, which is often what you are trying to do in a PA or
loop-matching transformer - you may well find that you end up with windings of less than 1 turn! In these cases the inductance or the required turns ratio becomes the determining factors. In the more normal situation where you are trying to design a transformer with an economically-sized core for a given power level, the inductance is usually large enough not to be an issue, as Andy stated.
At 9kHz however, the 60turn winding is quite reasonable from the inductance point of view, giving 9.7mH and about 550ohm reactance. Also, the core losses would be lower at 9kHz, so you could allow a higher flux density and reduce the number of turns (or increase the power level, which might be better!)
Cheers, Jim Moritz
73 de M0BMU"
To aid calculations in future I have produced a small spreadsheet to work out the secondary turns from the input data (freq, cross sectional area and RF power out)."The magic equation is Vrms = 4.44.F.N.A.B all in SI units.rearranged Nmin = V / (4.44 . F . A . B)Al is irrelevant for transformers.Use a Bmax of 0.1 Tesla for Ferrites, allowing a decent safety margin.Your A (of 25 mm^2) = 25*10^-6 , F = 137000,25W in 50 ohms is 35V"
|OXO schematic on the G3PTO website|
Often, new discoveries in science are counter-intuitive and they do not sit comfortably with our experiences. One of these is quantum mecha...