Re: LF: XPQ WSPR15 475/136 and warm ceramic feed thrus

[John Andrews <w1tag@charter.net>]

I remember a graveyard maintenance shift many years ago, when my boss observed that a braid wire connection clipped onto a coil in a MF power divider was looking kind of shabby. Not being able to find a piece of flat copper, he tried length of stainless steel "Wraplock", which started out nice and shiny. After a few minutes of operation, it got very warm, and turned black. We quickly located some copper. 

John, W1TAG

On Oct 24, 2015, at 7:52 PM, Alan Melia <alan.melia@btinternet.com> wrote:

Well there is a cohort of noble men who have set fire to, window frames, fences, sheds, tuning boxes etc with 136kHz RF over the years :-)) plus minor infringments like rope guys, and waste-pipe spreaders .....I think the badge should be the usual symbols of earth, coil, and aerial but with a couple of small flames licking out of the bottom of the coil :-))  Yeah well a bit of artistic licence maybe :-))

 

Alan

G3NYK

 

----- Original Message -----

From: Laurence KL7 L

To: rsgb_lf_group@blacksheep.org

Sent: Sunday, October 25, 2015 12:04 AM

Subject: Re: LF: XPQ WSPR15 475/136 and warm ceramic feed thrus

Thanks Alan - absolutely - and I should have read the tables!

 At the beginning of testing I ran the Tx at full throttle for a few hours at 1.4Kw and measured the heating of components with an IR "laser" and saw a few degrees in increase but little more than when I measured in okie - obviously over time something odd happened! Its been running virtually constant for about a week...    Fire in the wire! 

Im now going to come in thru a plated out plastic bulkhead as it ended up last time and direct connect to the bus bars...

Think telephone exchange with a little more kick!

As ever its a learning curve :-)

Cheers

On Oct 24, 2015, at 14:50, Alan Melia <alan.melia@btinternet.com> wrote:

Hi Laurence my book gives Stainless Steel as 8 times  resistivity of Brass and 40 times  that of pure copper so maybe you were pushing your luck a bit, though I would have thought the connections at the ends would be problem. It looks like arcing on the pic but its obviously not..... the eramoc got so hot is just melted its  way though the plastic and it is cooked plastic on the outer surface. Also its not bulk resistance at these freqs you have to consider skin effect in the SS. Still interesting its only one insulator. It might be interesting to look at it with a milliohm meter if you have such a beast. I would guess you must have had the equivalent of 0.2 ohm or so to get that hot....particularly in your climate :-))

 

Alan

G3NYK

----- Original Message -----

From: Laurence KL7 L

To: rsgb_lf_group@blacksheep.org

Sent: Saturday, October 24, 2015 11:05 PM

Subject: RE: LF: XPQ WSPR15 475/136 and warm ceramic feed thrus

Thanks Alan - th iono really hadnt cooled off up here from the continuous heating over the past month or so but it was getting better so I thought Id better inject a little more heat

http://kl7l.com/coupler3.jpg

The Stainless 5/16th bolt in the feedthru must have had some imperfections in manufacture and got extremely hot at circa 50-60A :-) it didnt happen to the other bolt and wasnt at the wire connection points each side.

 I think Ive had it with feed thrus' at this current and are going to come straight in thru a hole drilled in a hi density cutting board. 

I recall the original brass feed thrus getting a little warm but this must have got real warm - sufficient to say the Decca kept on transmitting and didnt see a high SWR at all over the past week...

The Walmart Rubbermaid box was (is)  in its 12th year and Im just going to plate over it... :-)

Laurence KL7L WE2XPQ

---

From: alan.melia@btinternet.com
To: rsgb_lf_group@blacksheep.org
Date: Sat, 24 Oct 2015 22:42:47 +0100
Subject: Re: LF: XPQ WSPR15 475/136

Hi Markus, yes I think that has been happening, but in Laurence's case the first post did not appear to any of us so that was probably bounced on theway in, but I have seen cases were posts have been reflected but not received by the sender. Some ISPs seem to regard a message sent to self as spam.....I regularly dig out my LF postings from my webmail spam folder. Marking them as "Not Spam" does not seem to affect the rules in "Spamguard", the filter used.

 

I reckon you are due for a few down days Laurence the CME from the C5 on the 22nd arrived at 1900z. Spaceweather maked it as arriving unexpectedly early.....I dont see that the interval was about 62 hours. We only caught the "wash" as it was not pointing at Earth, and that could account for some of the longer interval.

 

Alan