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Author Topic: Doesn't vacuum variable flange resistance hurt magnetic loop performance?  (Read 3044 times)
AA5TB
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« Reply #15 on: March 24, 2013, 11:04:44 AM »

Si,

I believe in your experiences.  However, keep in mind that these small Hi-Q loops couple into other circuits very easily at a surprising distance.  That being said your antenna system may actually be more than you can imagine.  If you have a resonant full sized dipole in the vicinity of your small loop there is a strong possibility that the dipole is enhancing the performance of your loop.  The only way to truly tell is to have the loop out by itself several wave lengths away from anything else or at least orientated to minimize coupling.  It might be interesting to open and short the feed line to the dipole when listening on the loop and see if you detect any differences.

I know my loops have always "seemed" to perform much better than they should when indoors.  In all likelihood my small loop antenna may couple tightly with at least some of the home's electrical wiring enhancing the size of the antenna.  Of course this should be detectable by analyzing the bandwidth and radiation resistance I would think but I haven't gone so far as to do that.

As one who often operates QRP I know that when conditions are good it takes an amazingly small amount of effective radiated power to communicate around the world on HF.  With good operating skill you can make amazing DX contacts with about any antenna and that is why so many people disregard QSOs as proof of an antenna's performance.  On the other hand, if it works as well as you want it to then 'so what'.

It sounds like you're having fun so keep at it.  Very few hams are in a environment to properly evaluate an HF antenna's performance but if it seems to deviate greatly from theory than you need to take everything into consideration before claiming that people make too much out of the theory.

Carl Sagan often said "Extraordinary claims require extraordinary evidence" and I honestly believe that but I've been guilty myself on many occasions when extolling the virtues of my latest antenna. :-)

As a side note I use to experiment with small loops at high power just so I could see where the weak points were.  Lossy parts would get hot and points with a low voltage breakdown would arc.  You would be surprised at how hot things some things would get that I thought were good (high voltage door knob capacitors, thick braided conductors, etc.).  I once caught a capacitor made from RG-213 coax on fire!

Have fun.

73,
Steve - AA5TB
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G7DMQ
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Posts: 40




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« Reply #16 on: March 24, 2013, 04:58:21 PM »

Thanks Steve,

I've had my share of things catching fire too!  I'm never one to accept that what I've got is good enough - and that's what drives me to experiment!

It is perfectly possible the loop is coupling to either of the two long wire antennas (end fed and dipole), the other loop or even the VHF ones, the wiring or the double aluminium garage door!

However, I'll get my 'proof' when I take one on holiday.  That's the reason for my interest in loops - something I can use mobile.  Hopefully I'll get an idea how it really performs.

Si
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