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70 cm. and above

R

rfoverlord

guardian of freedom
Jun 1, 2005
752
5
28
daegaba system
anyone build any ants. for 440mhz and up? outside of a dipole and a 1/4 wave vert. thinking about a quagi, going to try and get it wide banded enough to to cover 440 and gmrs freqs. fm of course.
 

rfoverlord,
Haven't built one but there should be several examples in an amateur Handbook. Making it boradbanded enough for GMRS too will be a good trick, guess it'd depend on if it was strictly to listen with. Otherwise, a real good trick.
- 'Doc
 
Well, after reading this, I measured the 2:1 BW of my 11-element, 70cm Yagi. It was about 30 MHz! Seemed suspicious, so I took the driven element and the gamma off and cleaned it up real nice and put it back together. Same result!

Actually, the VSWR dives below 2 @ ~420 MHz, then squiggles along down to about 1.13, then comes up to about 2.2 @ 450 MHz, but takes another sharp dive down to about 1.5 @ 462 MHz and proceeds back up off the scale.

This sounds ideal for your application, assuming the thing is even radiating. I'll have to post the plots in another thread for a good work over. Get your whips warmed up! I'm gonna post another de-normalized Smith plot.
 
C2 said:
Actually, the VSWR dives below 2 @ ~420 MHz, then squiggles along down to about 1.13, then comes up to about 2.2 @ 450 MHz, but takes another sharp dive down to about 1.5 @ 462 MHz and proceeds back up off the scale.
Click to expand...
The fact that you have a low VSWR spot out of the designed bandwidth of the antenna only means that your transmitter will be happy. It is very likely that you will have no gain, or negative gain, in the desired direction. BTDT

Rich
 
That's true, maybe it is no more than a radiating dummy load!

That's why I dissasembled and cleaned the matching device and feed, it was not at all what I was expecting to see.

The plot will be worth scrutinizing.
 
well now that i will be getting some time off i'l try putting together a quagi and see how it works. maybe next month i will buy an mfj 269 so i can actually tune the thing since i don't trust my swr meter for those freqs.
 

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