[50mhz] RE: Home-Brewing a 50 MHz Dipole

[cboone@earthlink.net]

n5wbi@clearsail.net wrote:
> 
> Let's see ... Eight responses in less than 2 hours!  Awesome!
> 
> Thanks to everybody who replied!  Here's a synopsis of the
> responses that I received.
> 
> [1]  Check your coax to make sure it and the connectors are
> in good shape.  Coax and connectors degrade over time.
> 
> [2]  Make sure that the length of your coax feed line is
> ODD multiples of 1.4 wavelength.

NO, ODD multiples of 1/2wavelength...a 1/2wl in any line
shows the same Z (line impedance) from one end to the other..
any other length will cause a change in apparent impeadance
and hence SWR
 
> [3]  Use 9913 flexible coax instead of the RG-XX type.

Any good quality coax will do...

>[4]  Cut the dipole legs too long to begin with, then trim
> as you tune.  Use the "sweep" method (with proper ID's, of
> course) to check the SWR as you move up in frequency,
> starting at 50.000 MHz.

Good idea but the 468/freq in MHZ x 12 = lnegth in inches
is good enough...you can always add wire.....OR strip the ends
and just fold back the ends (tied in a small loop and make sure
its wire to wire!) and let out the ends if you need to 

> [5]  Adjust the cut length of each dipole leg for velocity
> factor (if you're using insulated wire).  The velocity
> factor is around 0.9, so the equation becomes 468/F * 0.9
> Or, you could use the standard equation and trim for best
> SWR.

Nope! VF does NOT really come into factor here...the thicker
the wire, the wider the bandwidth of the antenna (the lower
the Q)...At 50MHz, you wont see much difference....though it
can cause problems at higher freqs...


Chris
WB5ITT
Asst Radio Chief Egr
Liberman Broadcasting, Houston
FCC PG-9-5322 commercial