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Monday, 30 December 2013

Which one do you trust?

Well,

The linear that I started way back here:

http://g0mgx.blogspot.co.uk/2013/11/now-that-smoke-has-settled.html

is almost complete, I've done my best to calibrate the input power detection circuity and will certainly "trip" into an alarm state if I overdrive the amplifier brick. I have also calibrated a simple directional coupler on the output to give me both forward and reflected power indication.

I needed to understand the match that my antenna gives me on 4M, but the Antenna Analyser that I bought some months ago only goes as far as 50MHz and the other MFJ unit that I share with Vince, G0ORC seems to have a gap in the tuning at exactly the 70MHz band.

So, I used the return loss bridge from here:

http://g0mgx.blogspot.co.uk/2013/09/return-loss-bridge-where-does-it-lead.html

and explained how to use it for SWR measurement back here:

http://g0mgx.blogspot.co.uk/2013/10/so-lets-get-bit-smarter.html

So, hooking the antenna from here:

http://g0mgx.blogspot.co.uk/2013/05/thatll-never-work-will-it.html

we see this:


and focusing right on the 70MHz allocation only:


So, whilst it's not perfect, the antenna is a good match across the whole band. As the MS frequency it looks to be 1.3:1 - which is more than acceptable.

I need to introduce you to two new residents at G0MGX, they are Mother and Son, please meet Pepper and Freddie:

 

Fun, egh?

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