[Lowfer] [rsgb_lf_group] 2200m dynamic load

[k3mf at aol.com]

 Brian,
     I use #77 material.
73,
Wayde K3MF

 

 

-----Original Message-----
From: Brian, WA1ZMS <wa1zms at att.net>
To: rsgb_lf_group <rsgb_lf_group at yahoogroups.co.uk>
Cc: Lowfer <lowfer at mailman.qth.net>
Sent: Mon, Apr 2, 2018 9:50 am
Subject: Re: [Lowfer] [rsgb_lf_group] 2200m dynamic load

Rik, et al.-I'm leaning now towards it being a corona issue. Both amps are just fine into a dummy load. The spectrum analyzer shows things well behaved into a load and the output looks like a very clean sine wave on the 'scope.At one point last nite, I noticed what is best described as "very tiny fuzz" on the very top and bottom of the voltage waveform while into the antenna and over about 250w into the antenna.  (The modified Hafler 9505 audio amp will deliver 700w into the load w/o issue).  That fuzz or fur on the crests may be something breaking down under voltage.The very same antenna (a 160m dipole at 60ft feed with 4" open wire) has been used by me for years on 630m up to 200w CW.  So only the new 2.55mH variometer and the QSY to 2200m is different. Same Hafler amp as well.  While my mind was blaming the ground system as being dynamic with 137kHz RF, I'm now starting to suspect that corona might be the issue.  The antenna always measures -25dB S11 on 137.78kHz with the HP8753D. So small signals are fine. Resonance is classic curve right through the center of the Smith chart.I need to go back and rethink the peak voltages on the top hat and it could very well be an end insulator which is at issue. Or I could just let it run and see which tree catches fire first. hi....hi....Next Q: Which mix of ferrite have folks used as current xfmr in your scopematch?  I have plenty of #2 material and some #77, #61, etc..  My goal would be a few hundred nH per secondary turn and then use 50T and the 1T primary.-Brian, WA1ZMS> On Apr 2, 2018, at 7:11 AM, Rik Strobbe rik.strobbe at kuleuven.be [rsgb_lf_group] <rsgb_lf_group at yahoogroups.co.uk> wrote:> > Hello Brian,> > 40 Ohm groundloss on 137 kHz is not too bad, I am suffering with 130 Ohm groundloss!> About the changing loss resistance: apart from what is already mentioned (connectors, corona) it might be worth to have a look at any cap's or inductors in the high power part. These may warm up and change value.> If you have an appropriate dummy load I would suggest to run the TX at full power into the dummy load. If the changes appears then as well you have to check inside your TX, else outside.> > 73, Rik  ON7YD - OR7T> > Van: rsgb_lf_group at yahoogroups.co.uk <rsgb_lf_group at yahoogroups.co.uk> namens 'Brian, WA1ZMS' wa1zms at att.net [rsgb_lf_group] <rsgb_lf_group at yahoogroups.co.uk>> Verzonden: maandag 2 april 2018 2:39> Aan: Lowfer; rsgb_lf_group at yahoogroups.co.uk> Onderwerp: [rsgb_lf_group] 2200m dynamic load>  >  > While trying to get a bigger PA set-up today on 2200m, I ran into a problem which is rather odd. It would appear that my ground losses are a function of RF currents flowing.> > Has anyone seen such an effect with rather lossy ground at LF?> > That fact that the load Z shifts and thus detunes any PA driving it (I have tried two different PAs) makes for more chasing one's own tail when measuring Z both inside and out at the antenna. My ground losses on 2200m are on the order of 40 ohms so that's part of my root problem! Time to build a 2200m Scope match I suspect.> > Comments?> > -Brian, WA1ZMS> iPhone> __._,_.___> Posted by: Rik Strobbe <rik.strobbe at kuleuven.be>> Reply via web post	•	Reply to sender	•	Reply to group	•	Start a new topic           	•	Messages in this topic (6)> VISIT YOUR GROUP> • Privacy • Unsubscribe • Terms of Use > .>  > > __,_._,_________________________________________________________________Lowfer mailing listHome: http://mailman.qth.net/mailman/listinfo/lowferHelp: http://mailman.qth.net/mmfaq.htmPost: mailto:Lowfer at mailman.qth.netPost must be less than 50KB total for message plus attachment!This list hosted by: http://www.qsl.netPlease help support this email list: http://www.qsl.net/donate.html