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Date: Tue, 25 Jan 2011 13:29:11 +0000
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From: Andy Talbot <andy.g4jnt@gmail.com>
To: rsgb_lf_group@blacksheep.org
DomainKey-Status: good (testing) 
Subject: LF: WSPR Beacon
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The power of my WSPR beacon on 503875Hz has gone up by approximately 4dB.
Now running the Class E PA.

Thanks for tentative offes of thicker Litz wire, but on reflection, looking
at the resulting coil dimensions needed, there isn't much scope for a larger
coil diameter without a major chassis rebuild.

The tank coil heating and resulting detune problem were mostly-solved by
making up a plastic moulding to duct air from the fan round to the coil.
All a bit Heath-Robinson, but it can now run at the 500 Watt output level at
room temp without undue runaway.   And is certainly OK for the low duty
cycle WSPR transmissions its intended for.

Now outside in the shed, at lower ambient temperature so I'll probbaly be
confident enough to leave it runniing without dashing outsuide too often to
check.
There is scope for another dB or even perhaps two by winding the Vdd up to
55 or 60V, but I won't tempt things too much.  The antenan impedance is a
bit over 50 ohms, so power output is lower than into the test load, but
still in excess of 400 watts.

And talking of test loads.    The 1kW 1GHz Bird attenuator increases its
attenuation value as it gets warm.   I was wondering why power levels
appeared to be falling after a period of testing at max power when DC and
temperature were all pretty constant.    A recal using DC when
the power-attenuator  was hot, showed more than 0.5dB additional attenuation
over its cold value.    Not at all satisfactory.    I'm now using on a
voltage / current monitoring bridge for power measurement - that is more
reliable.

Andy
www.g4jnt.com

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<div>The power of my WSPR beacon on 503875Hz has gone up by approximately=
 4dB.=A0=A0 Now running the Class E PA.</div>
<div>=A0</div>
<div>Thanks for tentative offes of thicker Litz wire, but on reflection,=
 looking at the resulting coil dimensions needed,=A0there isn&#39;t much=
 scope for=A0a larger coil diameter without a major chassis rebuild.=A0</d=
iv>
<div>=A0</div>
<div>The tank coil heating=A0and resulting detune problem were mostly-solv=
ed by making up a plastic moulding to duct air from the fan round to the=
 coil.=A0 All a bit Heath-Robinson, but it can now=A0run at the 500 Watt=
 output level at room temp without undue runaway.=A0=A0 And is certainly=
 OK for the low duty cycle WSPR transmissions its intended for.</div>

<div>=A0</div>
<div>Now outside in the shed, at=A0lower ambient=A0temperature so I&#39;ll=
 probbaly be confident enough to leave it runniing without dashing outsuid=
e too often to check.=A0=A0=A0 </div>
<div>There is scope for another dB or even perhaps two by winding the Vdd=
 up to 55 or 60V, but I won&#39;t tempt things too much.=A0 The antenan im=
pedance is a bit over 50 ohms, so power output is lower than into the test=
 load, but still in excess of 400 watts.</div>

<div>=A0</div>
<div>And talking of test loads.=A0=A0=A0 The 1kW 1GHz Bird attenuator incr=
eases its attenuation value as it gets warm.=A0=A0 I was wondering why pow=
er levels appeared to be falling after=A0a period of testing at max power=
 when DC and temperature were all pretty constant.=A0=A0=A0 A recal using=
 DC when the=A0power-attenuator =A0was hot, showed=A0more than=A00.5dB add=
itional attenuation over its cold value.=A0=A0=A0 Not at all=A0satisfactor=
y.=A0=A0 =A0I&#39;m now=A0using on a voltage / current monitoring bridge=
=A0for power measurement - that is more reliable.</div>

<div>=A0</div>
<div>Andy</div>
<div><a href=3D"http://www.g4jnt.com/">www.g4jnt.com</a></div>
<div>=A0</div>

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