HF BANDS QRP LINEAR AMPLIFIER

Ivan wrote:BTW, everyone knows that USB = Universal Serial Bus

VBR from Ivan

... unless you are in the medical trade, there it is UltraSound-guided aspiration Biopsy.
United States Bank
United "eye-candy" Boys (true !!) [forum word-filter changed the S word to eye-candy  ]

Funny how abbreviations can have loads of different meanings.
My employer have an internal "Acronym finder" function on their internal homepage. When I keyed in BBC the first entry was the Belfast Boat Club. The British Broadcasting Company was about fourth down the list! (probably because they were sorted in alphabetical order)

In the telecom industry MSU means Multi-Subscriber Unit, but the first time I used the term (early 70's) it meant Mid-Stream Urine (sample)

Over the past 8 weeks my circumstances have changed, so in the house and garden I try not to use DIY. Whenever I can I use GSETDIFY (Get Someone Else To Do It For You)

But you have a nice day, Ivan.
BR Harry - SM0VPO sm0vpo

Oh, the Swedes are real masters of long words!   I remember a very long German word:
"die Hotentotenpotentatentanteatentatentater", which means "the man who performed a political attack on the aunt of a leader of Hotentots". I hope I did not make too many mistakes. German sentences are said to tend to become one long composed word and the preposition at the end.

BTW, everyone knows that USB = Universal Serial Bus

VBR from Ivan

Hi Ivan,
When you talk about impedance (resistance to an alternating current) it sounds simple, but as soon as you start using the term in, say, matching to the base of a transistor, then it becomes quite complex because there are other factors to take into account that afftect the impedance load on the previous stage. But I also understand that technical language can be a problem.

Swedish can also be quite confusing with basic radio terms, for example, when we talk about single sideband.

English:
USB = Upper sideband
LSB = Lower sideband

Swedish:
ÖSB = (övre sid bandet) = Upper sideband
USB = (undre sid bandet) = Lower sideband

In general speech the Swedes have a nasy habit of putting together words, which can sometimes be confusing. The calssical word is "kungsängen" can be divided in two ways:

Kungs-ängen (the king's meadow)
Kung-sängen (the king [sized] bed)

My favourite Swedish word that is a concaternation of many words is "flaggstångsknoppsförgyllareslärling". Often quoted as being the longest work in Swedish. It means:

The aprentice to the man who puts the gold paint on the knobs on the top of flagpoles.

It is not the longest. The longest word in Swedish is:
"nordvästersjökustartilleriflygspaningssimulatoranläggningsmaterielunderhållsuppföljningssystemdiskussionsinläggsförberedelsearbete"

I believe it means:
"North-westerly sea coast artillery flight tracking simulator installations material maintenance system scheduled discussions before partial work preparation"

Now you can imagine how the Swedish scientific and telecom community like to use big words. I try to avoid speaking to Swedish radio engineers in Swedish if I want to understand them.

Very best regards Harry - SM0VPO sm0vpo

Hi Harry,
thank you for clarification. The Czech language uses the word "impedance" for the complex number Z = R + jX or maybe for its modulus |Z|. A purely inductive impedance is named "induktance", while a purely capacitive impedance is "kapacitance". Yes, we write and read it with k, not c. The fact that "induktance" means the other parameter than "inductance" may make me confused a bit when changing my mind between both languages.

VBR from Ivan

Hi Ivan,
That was a very good question. It is easy for the experienced to differenciate in text. I know that I frequently make mistakes when the brain is working faster than the mouth or fingers on the keyboard.

Inductance - Henries - the actual value of the inductor
Impedance - the electrical "resistance to AC" at any given frequency

I know that I sometimes mix the two when I am stressed and want to get the info into script.

BR Harry

Hello Harry and all,
I encountered a language problem bound with this topic. Talking about coils, I use these parameters:
L expressed in henry (H, more often uH or nH), called "indukcnost" in Czech, and
XL = 2*pi*f*L expressed in ohms, which is "induktance" in Czech.
Which of these parameters is "inductance" in English? And how should I call the other one?
I want to avoid misunderstandings

VBR from Ivan

Hello Giorgio,
The inductor is exactly as Ivan stated, not very critical.

If you want the amplifier to operate at 1MHz then you need a larger inductance so that the coil impedance is at least 5x the impedance of the load. If the inductor is too large then inter-turn capacitance will degrade the performance at 30MHz.

That particular inductor gave a very high inductance of about 12uH, which is perfect for the 7MHz band. Many ferrites designed for RF work have a lower inductance for a given number of turns, but work well into the VHF region. Ferrites designed for power supplies can give a very high inductance with just a few turns.

I have done a lot of work with unknown ferrites, and most of my projects using ferrites were tested using a signal generator and an analyser to check the inductor had a low loss at the frequencies of interest. This particular project used a ferrite of with unknown characteristics, but the ferrite was physically large, so the inductance was high.

You can normally expect an RF ferrite to work with up to 20:1 frequency ratio. If you can accept a little loss outside this region then a ferrite output transformer can realize a 30:1 ratio.

The purpose of this project was to demonstrate a method of winding a 2-hole ferrite to get a wide frequency range and reduce the inter-turn capacitance. It is basically a 1:4 impedance auto-transformer. You can wind such a transformer in the conventional way using two wires of wire (biflar).

Very best regards from Harry - SM0VPO sm0vpo

Ivan wrote:Hi Giorgio,
I did not find the article you have in mind, but I expect the coil value is not very critical. I guess you can try a coil with the same inductance at 1 MHz, i.e. a 50uH one.

VBR from Ivan

Thank you, I'll try my experiments with this value
The article I refer to is the classic : http://sm0vpo.altervista.org/tx/linear.htm
Also, in my AM transmitter project, I'm been inspirated from Harry's CMOS sinth for designing the PLL stage

Best regards
Giorgio

Hi Giorgio,
I did not find the article you have in mind, but I expect the coil value is not very critical. I guess you can try a coil with the same inductance at 1 MHz, i.e. a 50uH one.

VBR from Ivan

Which circuit are you talking about? Could you post a schematic? If you just need a linear amplifier then two IRF510 in push-pull configuration should be enough for 2W carrier and 8W PEP at 12V.

Hi all,

a question about 5uH coil :
I need to use this PA for an experimetal low power trasmitter in AM broadcast band for a community radio because in my country (Italy) this band is de-regutated from several years and its use is not explicitally forbidden

Harry wrote "... The idea is to get a reactance of about 300Ω at 10 MHz ..." but in my case the lower freq is about 500 KHz while the higher is about 1650 KHz

I think to increase the inductance value but I need help for which freq I calculate 300Ω  reactance

Best regards
Giorgio