"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"
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| OXO schematic on the G3PTO website |
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| 12W red LEDs for optical beaconing |
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| The current G3XBM operating station |
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| The weak trace seen by OH1LSQ on 500kHz this evening |
Mode T/R TxT df tsym BW S/N*
(m) (s) (Hz) (s) (Hz) (dB)
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How quickly K1JT can do the necessary coding will depend on his work load - he is a Nobel Prize winning physicist - but we are looking forward to the first release of this software in the coming months. |
| DX reports on 500kHz WSPR this evening using the new 10W transverter |
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| 500kHz WSPR reports map |
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| http://www.qrptransceiver.com/website |
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| The lastest transverter schematic (there may be value errors) |
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| WSPR reports 20.9.12 with the above transverter and 6m long antenna |
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| The desktop 472/500kHz station, ATU (don't laugh!) and antenna current meter |
Like many these days, I've an Apple iPod Touch and use it every day for web browsing. When watching the TV or reading the paper it is handy to be able to check my WSPR spots with a quick look at the iPod Touch. 
.jpg/240px-Milvus_milvus_R(ThKraft).jpg)
For the last month we seem to have been away from home half the time. The last few days we have been in Yorkshire for a sibling reunion with my wife's brothers.
"The current prediction for Sunspot Cycle 24 gives a smoothed sunspot number maximum of about 76 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."Looks like they are expecting a double peak cycle with a slightly larger peak about a year from now. We'll see. The peak is likely to be very low compared with mega-peaks seen in the last half century.
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| Updated schematic (an error spotted by G3TFX) |
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| Breadboard of WISPY TX - 50mW pep WSPR (100mW DSB) |
The FLEX-6700R™ Signature Series receiver is based on a new hardware architecture and SmartSDR™ software platform. This hardware uses Digital Down Conversion (DDC) to convert from RF to digital. The FLEX-6700R uses two Spectral Capture Units™ (SCU) for the RF to digital conversion and an ultra high performance on-board signal processing and control system to perform demodulation, filtering, and audio stream management. The result is incredible receiver dynamic range and received signal clarity.
Now I know there are people around with too much money and there are some applications when a very good receiver may be of benefit, but would YOU spend £4799.94 on one? This is just the receiver remember! No thanks. I'll continue to build simple rigs for a few pounds and accept their limitations.The FLEX-6700R model receiver utilizes two SCUs for reception from 0.33 to 77 MHz plus 135 to 165 MHz and the ability to create up to 8 full featured independent SLICE RECEIVERS. Optimized preselector filters can be selected for the ham bands for greater out of band rejection.SmartSDR is the “ecosystem” of the radio platform. It organizes all the signal processing power in the radios into an advanced radio fabric. SmartSDR understands the capabilities of each SCU and how to harness its power. It also comprises of the “presentation layer” or GUI client that the user interacts with. The FLEX-6700 utilizes an Ethernet connection for high-speed “driverless” access to the graphical user interface (GUI).
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| The EnOcean evaluation kit (for professional developers) as shown on their website |
