It was a while ago I sent that e-mail & still havn't got round to sorting
the 136 antenna although I am part way there as I have started constructing
a 5 spoke spiral (larger diameter than the previous 4 spoke spiral) so as to
be able to "basket weave" the spiral. I did some experiments in a smaller
test format & found that there was more inductance with basket weave
arrangement over the double spiral when using the same amount of wire.
It is true about the dummy load versus antenna situation but it did enable
me to bench test the modified PA first.
Jim's phase meter is an excellent device for LF & as Jim pointed out it can
be used at the transmitter or antenna end without any differences in
readings so it is great for setting up the tuning remotely from the shack (I
have my variometer motorised). By the way Mal, I did modify my LF antenna
loading coil in the way you suggested some while ago & was able to get a
very good match.
I don't have any spare diodes, I purchased my BAT85's from CPC Plc in
Preston (part of the Farnell Group) so you should be able to get the BAT85's
over your side of Pennines from Farnell (they were 27 pence each).
I have recently been stripping out the bathroom & I am almost finished
tiling & refitting (it's been 20 years since that room was touched) so I
hope soon to be able to devote more time to the hobby.
Gary - G4WGT - IO83qp
Web : http://myweb.tiscali.co.uk/wgtaylor
From: [email protected]
[mailto:[email protected]]On Behalf Of hamilton mal
Sent: 05 May 2005 13:45
To: [email protected]
Subject: LF: Re: RE: Re: Re : tests.
----- Original Message -----
From: "Gary - G4WGT" <[email protected]>
To: <[email protected]>
Sent: Monday, March 28, 2005 8:48 PM
Subject: LF: RE: Re: Re : tests.
Hi Mal & LF,
I am using the G0MRF 300 watt Tx but since blowing several PA mosfets I
decided to carry out the M0BMU PA mods using the original toroid & I can
run a cool PA up to 650 watts into dummy load bench testing. I put it on
into antenna & started with 280 watts & on following tests gradually
increased to 420 watts (still cool) with antenna current up to 2.3 Amps it
was at this time I got corona/arcing on the spiral top load so I stopped
tests until I have the time to lower the mast & carry out a visual
inspection of the area of arcing so as to effect a cure. I suspect that I
may have too little clearance between the spiral & the metal fixing
hardware, an inspection will be carried when work & family permit.
Gary - G4WGT - IO83qp
I have found soak testing into a dummy load different to loading into the
resonant antenna. The antenna is more critical and tricky and seems more of
a problem using high voltage low current than low voltage high current.
I built my tx a few years ago when 136 khz became available, it was the low
V type and it worked well over the years but recently tried different hi
spec FETS 23A/600V. I ran it up to 50v at 20a but it does not appear to be
as stable as the low voltage tx. I think others might have experienced this
How does the phase meter work that you built. I have a couple of nice meters
here that would be suitable and hope to build one. One thing I do need are
some diodes. If you have any spare from your project and want to sell a few
let me know. I have everything else.
73 de Mal/G3KEV