EMRFD Message Archive 7913

Message	Date	From	Subject
7913	2012-11-05 18:32:52	jor	Question; can the LD MOS Fet PD85004 be used for a HF PA am
Hi all, I want to build a SMALL SMD balanced low power HF broadband PA amplifier approximately 3-4 watt RF output. I think to use the PD85004 LD MOS transistor from Microelectronics, data given is 4-watt output bud on 870 MHz. The Power versus frequency graph is bending down on either side from this 870 MHz . I wander if this transistor in SOT89 SMD can be used for 1-30 MHz frequency's even at a litle lower power output. Have anyone experience with this type of UHF broadband transistor(s) used for HF ? Please info on this question. The data sheet can be found in the files map of PE1KTH. Thanks, 73" Joris PE1KTH
7914	2012-11-06 07:47:37	Graham / KE9H	Re: Question; can the LD MOS Fet PD85004 be used for a HF PA
Hello Jor: The spec sheet does not tell you if this part is suitable. It answers no questions about the HF performance. It only gives parameters for 800 - 900 MHz. The main question, (not answered in the spec sheet) is whether the part has input and output impedance matching inside the package. If so, they are not normally usable outside the intended frequency. If no impedance matching inside the package, then it is probably usable at HF. Your circuit will need to get rid of the gain above HF, otherwise you will have a lot of problems with VHF/UHF oscillations, particularly in a push pull circuit. It is probably worth trying. --- Graham / KE9H ==
7916	2012-11-06 09:21:54	Ashhar Farhan	Re: Question; can the LD MOS Fet PD85004 be used for a HF PA amplfie
use feedback? - farhan
7917	2012-11-06 16:06:30	Graham / KE9H	Re: Question; can the LD MOS Fet PD85004 be used for a HF PA amplfie
If you can control level and phase of the feedback over a 500 to 1 frequency range (9 octaves), while the output is connected to an antenna that can be anywhere on the Smith chart. Otherwise, I think you are better off dumping the gain above 50 MHz, so that it is unconditionally stable at VHF and UHF. --- Graham / KE9H ==
7918	2012-11-06 22:45:06	w6zba	Re: Question; can the LD MOS Fet PD85004 be used for a HF PA
Hi Joris, The following might help (schematic for a 144MHz amp using the PD85004): http://www.silcom.com/~pelican2/PicoDopp/MH33_MORE.html 73 and good luck. -Matt w6zba
7940	2012-11-23 10:05:56	Tim	Re: Question; can the LD MOS Fet PD85004 be used for a HF PA
I don't have experience with that particular part but other UHF power FET's do fine in that range as class C amps with (as necessary) some swamping of gate with parallel resistance to handle any instabilities. Adequately heat sinking these parts requires some careful PCB design. If you want something that is more tamely linear and suited to your 1-30MHz range, check out the RRD16HHF1. Most of my experience with this part is single-band tuned circuits and class C but there are a lot of push-pull nominally linear broadband designs out