[Amps] Input Impedance of RF MOS amp

[Will Matney]

Stefan,

If the map is one of those by RM Italy (aka Midland), it's definately really designed for the 11 meter band. It sounds that is what you have by it having a KL typr model number. If the case is red or gray with a black face, it probably is. Matter of fact, there's some special circuitry in the keying circuit to switch it to 11 meters with a simple jumper provided. To be honest, I highly doubt it working correctly on the lower frequencies without modifying it.

Best,

Will

*********** REPLY SEPARATOR  ***********

On 5/6/05 at 8:38 AM Stefan wrote:

>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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