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Homemade Radio Electronics
Antenna 1/4 wave Groundplane for 940MHz to 980MHz

Here is the compleete quaterwave groundplane for 940 to 980MHz

I used piano wires after I have measured and tested its uptimal dimentions using copper wires
this antenna can be dissassembled and shipped in a small package. quite smart

1/4 waves GP antennas have nice SWR over a good usable frequency range.
their gain is low, due to the radiation pateren is round and have almost no direction up/down too.
at the top direction you have a "black-hole" in the radiatern pattern, knowing this is a must
a low gain antenna have an advantage : it is just as good in almost ANY direction -
so they are often used in portable setups, where the direction to the other part is not known.

Another advantage is its design is coil and capacitor and match free, so its power handeling is close to infinite,
a tiny thinn wire antenna like this one, can handle hundreds off watts.

the construction:

An N connector is a nice platform for high frequency antennas
this antenna was made for the free ISM band used in USA (940-980MHz)
moving the feeder a few mm up/down will move its centre frequency a few 10Mhz, so measurements are critical.

to make a GP Antenna platform that will allow me to play with all dimentions as often as I like
I invented this screw on cable connector approch.

the dimention match metric : 300 / frequency in MHz = wavelength in meters.
now simply take that wavelength / 4, I measure from where the feeder is visible, then this calculations works fine for 500-1500Mhz
at lower frequency it is normal to multiply the length with 0.9 to 0.95 to get the actual length, this factor depends a bit on wire thickness and material used and the frequency

I sanded all parts for uptimal solderbility and screwed them on the N connector as straight as possible
placed the connector on an SMD heat plate and used a big powerfull soldering iron. note how well I got all threads centered behind the mounting holes ! lucky me

for the antenna feeder pin I used a bit smaller cable screw mount.

After soldering, I drilled the solder out of the inside, impossible to prevent it from going in there anyway
now my antenna piano wire will go in to the end, and can be mounted with both screws.

I used a thick layer of epoxy to strengthen it as much as possible, still I think a bit of caution must be keept so it dont brake.
maybe use thinner piano wire for the feeder, so it simply bend.

made: 14th of November 2008