Paul,
Thanks for your experience. A 20% low reading on topband would be getting
to the edge of my tolerance band. Hey, I bet Bird would make a special 1.8
to 30 MHz slug for members' of Amps if we made representations! I wonder
if it's internals would be any different from a H-series one?!!
I would like to think I could rely on the Bird kit (even when used
marginally out of band) to measure the stations RF out to better than 20%,
recognising that the 5% spec. may be optimistic in the view of
others. Personally, I have never had access to any test kit that caused me
to doubt / look further into the 5% claim - I swap inserts freely between
lines and meters and seem always to get readings in line with my
expectations. Even my cheap Daiwa meters seem to be within about 10-15% of
any Bird mix and match combo I have assembled. I would question the need
for accuracy much better than 10% in practice anyway. Of course, you could
calibrate a slug to a particular meter and use them thereafter only as a
pair. The cal. part is easy, so long as you have something better against
which to do the cal.!
It was suggested to me that the measurement error (HF vs topband, using
'H'-seies slugs) becomes more acute the smaller the power rating of the
insert. Perhaps the measurements you took on your 1000H vs 2500H is
supportive of this. My checking of a 2500H insert at only 1 kW was not
ideal. I do not have any 1000H, but I do have some 250H and will try these
when I get some time.
As I recall there was a site on the web somewhere where a dealer did a test
on a bucket of 2500H slugs and reckoned that they were in spec. He
probably didn't go out of band though.
Regards.
Mark.
-----------------------------------------------------------
At 10:00 21/03/2005, paul_group@greenrover.demon.co.uk wrote:
>In message <6.2.0.14.2.20050320182813.029a3c90@mail.plus.net>, Mark Hill
><g4fph@mjha.co.uk> writes
>>
>>Thinking about it, I'm not sure I have ever checked an H-series at exactly
>>1.8 MHz. Did you mean 1.8 MHz exactly, or were you just using 1.8 to refer
>>generically to topband?
>
>I recently repaired a GS35 amp for someone, it had gone bang while being
>used on top band.
>
>After the repair I found that it was fine on all bands but the efficiency
>and power out seemed a little low on 160m.
>
>I couldn't really find anything amiss with the amp so to verify things I
>compared my 1000H and a borrowed 2500H with my attenuators and HP437
>
>Sure enough the Bird elements were "near enough" on 3.5Mhz but on 1.8Mhz
>they both read low.
>
>I didn't write any of the figures down 'cos it was a one off measurement
>but my "in cal" 1000H read pretty much spot on at 3.5Mhz but circa 800W at
>1.8Mhz. It compared pretty well up to 50Mhz as well but the directivity
>isn't as good as my 1000B.
>
>Note my 1000B is no longer "in cal" but the meter still moves so it
>mustn't have realised :-)
>
>At 1500W the borrowed 2500H read just over 1Kw.
>
>I didn't measure either of the elements at exactly 2Mhz but I'd be
>surprised if the roll off starts in the first 200Khz below 2Mhz.
>
>Regards
>--
>73 de Paul GW8IZR IO73TI | Those who pay for bandwidth understand
>http://www.gw8izr.com | why we should only post plain text
>
>
*******************************************
Mark Hill - G4FPH
E-mail: g4fph@mjha.co.uk
Current web pages at: www.qsl.net/g4fph
Old web pages at: www.g4fph.freeserve.co.uk
-------------------------------------------
Dipoles resonant on 1942/3695/7065 kHz
2 ele delta loop beam resonant on 14180 kHz
-------------------------------------------
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S witch off
I solate
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