FW: [Antennas] Electrical length

Thu, 11 Jul 2002 10:37:52 -0400

Randy;
The MFJ-259/B/269 analyzer's are adequate for stubs. Always cut extra
lengths to compensate for variances in VF of the coax.
Place connector on one end and plug into the 259. Follow transmission
line stub procedure in the manual.
(Manuals may be downloaded free from MFJ's web page.)

Good luck,
Jim, K4SQR

On Thu, 11 Jul 2002 06:25:14 -0700 <[email protected]> writes:
> 
> 
> George/W5YR
> Thank you for your reply.
> So to do this ( my project is to make phasing lines for 144Mhz ) 
> then is
> to calculate 1/4 wave length 144/246 *(velocity factor)= length in 
> feet.
> (I'll be using 5/4) So do I then try to trim for electrical length 
> or
> should I leave extra for trimming? 
> Is my MFJ 259 accurate enough for this? 
> 
> Randy
> AC7NJ
> 
> -----Original Message-----
> From: George, W5YR [mailto:[email protected]] 
> Sent: Thursday, July 11, 2002 6:05 AM
> To: [email protected]
> Cc: [email protected]
> Subject: Re: [Antennas] Electrical length
> 
> Randy, the classical approach to this is to put an analyzer at one 
> end
> of
> the cable and find the frequency of lowest impedance. This for the 
> cable
> open-circuited at the far end. If the cable is shorted, then look 
> for
> the
> frequency of highest impedance. This will be the frequency for which 
> the
> cable is a quarter-wavelngth long.
> 
> With an open cable, the frequency of highest impedance indicates 
> the
> electrical length of a half-wave line. Of course, appropriate even 
> and
> odd
> multiples of these lengths will give similar results.
> 
> With an SWR meter, one looks for the frequency of highest SWR for 
> an
> open
> cable or a shorted cable since either provides a reflection factor 
> of
> unity.
> 
> I am not aware of a procedure that shorts both ends of the coax 
> unless
> they
> have in mind dipping a small loop formed in the short at one end.
> 
> 73/72/oo, George W5YR - the Yellow Rose of Texas         
> Fairview, TX 30 mi NE of Dallas in Collin county EM13qe   
> Amateur Radio W5YR, in the 56th year and it just keeps getting 
> better!
> QRP-L 1373 NETXQRP 6 SOC 262 COG 8 FPQRP 404 TEN-X 11771 I-LINK 
> 11735
> Icom IC-756PRO #02121  Kachina 505 DSP  #91900556  Icom IC-765 
> #02437
> 
> 
> [email protected] wrote:
> > 
> > How do I find (measure) the electrical length of a piece of coax I
> have
> > the Antenna Book it has me short the center conductor to the 
> shield at
> > both ends. The velocity factor is printed on the coax. NOW WHAT?
> > 
> > I have a MFJ 259 & Dip meter coils for it still in the box
> >
> 
> - - - 
> 
> Your moderator for this list is:
> Larry Wilson KE1HZ [email protected]
> _______________________________________________
> Antennas mailing list
> [email protected]
> http://mailman.qth.net/mailman/listinfo/antennas
> 