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Linux x86_64; rv:52.0) Gecko/20100101 Thunderbird/52.7.0 MIME-Version: 1.0 In-Reply-To: Content-Language: en-US X-Provags-ID: V03:K1:atQ0nhF+9da11uP9WJ9uJLHTPTPBMfgGd3Eem5tSOx8+MbszX+8 MEintRxu/1nYIUvPuCKmOr6/jeIDA1yhCGlaxEYwf4DfEJkpQuFkZkJTzoVEg0wssqjmrcB NHE1xtC+OQhtJjMMYUrkGI1Juru8jIq5avIWnNlstZlJ1qf6wLZYZ341Sti0KgG7zXwvd4s 0M4pKMpo3SatANy35C4xg== X-UI-Out-Filterresults: notjunk:1;V01:K0:tCxMwuw8+Ug=:dkaTcmotu0S3zQ9Cy8VJ8n /XzuILglW4E3zTcB0F/jLtIE0Sino9hob3rPcJdHFjnSwpM1mze3IJrPDghWNQvOiEVnRuU1A bc1OnRESbXcFrmk3RtoFGBEh45tfrC3U/Jktrk1KsQr9G766fKuYnbgWI0aLxUAQkY95uEyD/ rDvJ7HDs60WHNtSutH+z2pgy8r3YKlzdliq2Hi0v6uYLDI86YWw0JXCVZ7BSINyPoBb/zBwJs 2MtHKvCjFSRCkYerfrzKesRJfRP30goN2xFhn1S71ayulKn7iZWY7RcpMhDkG7cXbZ6Ex9rWS WduKNWMt3GmZ6AuMUE87rvRv4V1UFu4UNviLYYAVDL6rTIk/OXUi/QlN6hA0UepdRCBx/4b02 ujO23JnYXTnwI0/H1gSG3Migc/kyA9cExiLmGsP6NtZKO1RIm0zkwOmRV6muafQmtzAKaeaGx Eyi3dh7CeT+5geS3KFffHJ3Tr1jrzFVaIZ7MMaNHu21ukv+T6hCdp0vo7Pt0CHpmWQdzFJ+y3 eYTuoFCjPKnSWYR0eVtjXhFgSV8Am/BEdh/BIb9Oij5UyQkPgOWd1jXrt3eupdU5PJu9S1xMG 8QL8dieQuNXfxwF+6SVnSnbtmGXd8jIF0IumKK8rto/UpXnizAqAMLy+fNhYkqQBX3xxzV0uq 1+TTav8R5RorN7gJXbOvqqzQETbIKQ9xqqjmIcCDuEn+HJN93a+rpcwZ8u/DYg5qSaF+o2AKn D9npdQF7vyzuqyN03gI18R9Gz6HZuMQjihTqBlokZNsxqmVuhlPjp7zuLFY= X-Spam-Score: 0.0 (/) X-Spam-Report: Spam detection software, running on the system "relay1.thorcom.net", has NOT identified this incoming email as spam. The original message has been attached to this so you can view it or label similar future email. If you have any questions, see the administrator of that system for details. Content preview: Yep, voltage breakdown of the FETs was my worry. However I may be making a false assumption. I assumed the voltage spikes in the ringing would vary linearly with applied drain voltage? Perhaps that isn't necessarily so? [...] Content analysis details: (0.0 points, 5.0 required) pts rule name description ---- ---------------------- -------------------------------------------------- X-Scan-Signature: d7907c3bf895ca41e0bedc3fa074f0d4 Subject: Re: LF: W1VD amp help - more waveforms Content-Type: text/plain; charset=utf-8 Content-Transfer-Encoding: 8bit X-Spam-Checker-Version: SpamAssassin 2.63 (2004-01-11) on post.thorcom.com X-Spam-Level: X-Spam-Status: No, hits=0.0 required=5.0 tests=none autolearn=no version=2.63 X-SA-Exim-Scanned: Yes Sender: owner-rsgb_lf_group@blacksheep.org Precedence: bulk Reply-To: rsgb_lf_group@blacksheep.org X-Listname: rsgb_lf_group X-SA-Exim-Rcpt-To: rs_out_1@blacksheep.org X-SA-Exim-Scanned: No; SAEximRunCond expanded to false Yep, voltage breakdown of the FETs was my worry. However I may be making a false assumption. I assumed the voltage spikes in the ringing would vary linearly with applied drain voltage? Perhaps that isn't necessarily so? With 13V on the drains the first spike here is 'about' 64V. Efficiency seems fine. I wouldn't try to put an exact figure to it what with measurement accuracy in three places (voltage, current, RF power) but it 'appears' to be in the mid 90s. Paul On 04/09/2018 11:02 AM, jrusgrove@comcast.net wrote: > Alan > > The main concern about the ringing is that the positive extreme stays below the drain source > breakdown voltage ... with some 'headroom'. Otherwise ... > > Jay W1VD > > > ----- Original Message ----- > From: "Alan Melia" > To: > Sent: Monday, April 09, 2018 10:21 AM > Subject: Re: LF: W1VD amp help - more waveforms > > >> Paul >> I think you need to step back from this a little. One point, design/cable routing at 137kHz is >> normally not that critical and it is unlikely it is having much effect. Many us have ''haywired'' >> PAs at these frequencies without major troubles....even using croc-leads!! >> >> You are unhappy about the drain waveforms.......why?? the ringing is on the ''off'' device and so >> doesnt really matter in terms of efficiency. Consider what is happening. The FET drive goes off >> and the drain current starts to drop inductance in the drain feed causes the voltage to rise to >> try to keep the current flowing. Then on top of this the other transistor switches on and the >> transformer connection for the off side sees a rising induced voltage out of the transformer. >> There is bound to be overshoot but it does not absorb much power. It may be the generous ''dead >> zone'' (whilst a good idea) that is producing this picture. >> >> The critical part is the the flat zero volt line when the FET is on. The current pulse rings a >> bit, but the current drops in the second half of the pulse.....why?? This, I think, is really the >> loss of power. Does Jay's show this? The point I am making is don't get drawn up blind alleys >> because a trace just does not look ''pretty''. >> >> I think we have mentioned this before but the transient performance of the power supply may be a >> factor. There should not be great changes in the current draw because you are switching the PSU >> load from one transistor to the other but there can be higher speed transients that can affect >> power supply regulators in unexpected ways. >> >> As Andy said efficiency at 12v is not very meaningful because of the high rds of these FETs. It is >> usefull to run up a PA at low volts say for safety when the antenna needs to be tuned. >> >> Finally the scope probes are placing an. albeit small, capacitance across the drains (I am >> assuming they are correctly trimmed) The waveform can often be affected by where the ground is >> picked up from. >> >> Stick with it because you are close to being ''there'' >> >> Alan >> G3NYK