10 meter inverted V
Ok, so I'm building an inverted V antenna right now.
Basically, I have a chassis SO-239 with 24 GA wire soldered to the lead tip and to the shell ground.
I've got 50 Ohm impedance on the thing, but the SWR is reading infinity (It's an MFJ-259 analyzer) on the meter.
Is this ok, or is something wrong here (Bad solder joint, or something). Here's an ugly diagram of what I have:
* is the feedpoint
/ & \ is the antenna lines.
I'm feeding it from a second story window to about 5 feet off the ground.
Each line is 16.5" long, and the feedline is 20ft RG-58U pre-made cable.
What am I missing, or is this good to go, and ignore the SWR reading since I have a perfect match?
And if it's way wrong, any pointers about what is wrong?
Thanks in advance
RG 58/U is good for short runs (such as in a mobile radio installation environment) but it may become lossy and you may start experiencing performance issues when using too much of it. 20 feet doesn't seem excessive and it should *work* OK.
The design frequency for your antenna is wrong for typical 10m CW/SSB work. I would probobly revisit that measurement a little and redesign it for 28.300 mhz or cut each leg for 8ft 3 - 1/4"
A *high* VSWR reading may be a function of a nearby metal object or other unintended reflection. It seems indicative of *something* in proximity to the antenna causing a problem. That is if the antenna is designed and cut to specifications. I would try to get the ends up a little higher than 5 feet off the ground. Try for higher if you can but in no instance should the inverted V legs be closer than 45 degrees or it will start changing the antenna's feedpoint impedance characteristics.
Also be sure to keep the feedline at 90 degrees to the feedpoint. For example, it's not a good idea to run the feedline in the same direction as one of the legs.
A VSWR reading of *infinity* is typically indicative of an open or a short circuit somewhere in the connections. Perhaps one of the connectors have developed an internal short and it may require re installation and re-soldering.
A quick check using a VOM meter can usually reveal an open or short circuit in the feedline connections.
Last edited by KC8VWM; 04-25-2009 at 05:22 PM.
73 de Charles - KC8VWM
North American QRP CW Club #3159, SKCC# 5752
Thats your problem. Each wire should not be this long. For ten meters it should only be a bit over 8 foot long each wire.
Originally Posted by KC2UGV
AHA! Serves me for following the directions on a website blindly lol
Originally Posted by WB3BEL
Nevermind, I know what I did. Skipped the part where you "Take half of what the antenna formula spits out for each leg"
Silly me And I was wondering why this was twice the size of a dipole.
Last edited by KC2UGV; 04-25-2009 at 05:11 PM.
Thanks everyone for your help. After getting it down to 8.5" each leg, and clipping a combined 6", I got the impedance between 20-60 Ohms, and 1.7 or less across the 10 meter band
Why you have the Analyzer out, spin up to 14 to 18 MHz range -- should find a resonant point in that segment -- hey! 20 or 17 meters!
I'm probably missing something obvious, but why would a 10m half-wave centre-fed antenna show a resonance on 20m or 17m ?
Originally Posted by W9GB
I think and I could be wrong but a 10 meter 1/2 wave will act as a 1/4 wave on 20 meter. 14 MHZ x 2 = 28 MHZ Good luck with your dipole 10 M should be open with some E very soon.. Jim !!