[Amps] Input Impedance of RF MOS amp

[Stefan]

Dear Karl-Arne

You are completely right. The Amplifier fails in the lower frequencis (below 
14MHz). I am already looking at the motorola appplication notes (and the 
amplifier the same company has for HAMs).

Thank you very much.

73 de EA5FY
Stefan

----- Original Message ----- 
From: "Karl-Arne Markström" <sm0aom at telia.com>
To: "Stefan" <ea5fy at ure.es>; <amps at contesting.com>
Sent: Thursday, May 05, 2005 4:58 PM
Subject: Re: [Amps] Input Impedance of RF MOS amp


It is most likely that the KL300 is optimized for the 27 MHz range, as being
a CB amplifier. This usually means that the magnetic core area and number of 
turns in the input transformer may be insufficient  to handle lower 
frequencies.

The amplifier also lacks the compensation networks that are put into
wideband solid-state PA's to smooth out the gain variations over the 
frequency range.
These networks also helps to keep the input impedance reasonably constant.

In summary, I believe that the KL300 will need a rework according to the 
relevant
Philips and Motorola application notes covering wideband bipolar amplifier 
design.

73/

Karl-Arne
SM0AOM




----- Original Message ----- 
From: "Stefan" <ea5fy at ure.es>
To: <amps at contesting.com>
Sent: Thursday, May 05, 2005 4:06 PM
Subject: [Amps] Input Impedance of RF MOS amp


> Dear collegues
>
> Recently I was lucky enough to buy two KL300
> (http://www.rmitaly.com/scheda.asp?IDGr=1&cat=0&tipo=94) amplifier at a 
> flea
> market for a reasonable prize (2USD each) and I got them to work again. I
> have checked the devices with my FT817 and they work rather well (I know, 
> it
> does not have any output filters but I only wanted it for my FT817 to give
> it a punch, out there in the "wilderness" when carrying the appropiate
> battery).
>
> These devices are claimed to be useful for the whole HF band but I have
> noticed a quite non uniform output power over the HF bands. I think the
> reason is because my rig folds back its ouput power by noticing an 
> unmatched
> input impedance (the antenna is tuned or even a dummy load). Therefore I
> have the feeling that this amplifier does not have a flat input impedance
> (50 ohm). How can I flatten this impedance or what is done ususally to 
> solve
> this problems. I suppose that the input impedance is the input impedance 
> of
> the transistors (class B push-pull) plus the resistance put between the
> transistor's base and emitter (10ohm here).
>
> I would appreciate your suggestions and solutions. On the above web is not
> only the amp itself but also its very simple diagram.
>
> Thanks for your help.
>
> Kind regards,
>
> Stefan
> EA5FY
>
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