[SCCC] Phased verticals

[Bill Shell - N6WS]

Bob, Marty, & Kurt,

I don't mean to change the topic of Bob's thread here, but maybe you 
guys can answer a question I had regarding the use of 75-Ohm coax versus 
transformers for matching.  When I was putting together my phased 
verticals for 160m, I first used quarter-wave sections of 75-Ohm Coax 
for matching.  I found that the addition of the 'tuned' section of 
75-Ohm coax narrowed my usable 2:1 VSWR passband over what I realized 
from a single antenna.  I had built a 2:1 transformer to measure and 
test the 100-Ohm point to each antenna individually, so I could run the 
test with 50-Ohm tester. After seeing how the additions of the tuned 
sections of 75-Ohm cable narrowed the usable band for me on 160m, I 
decided to try testing the 2:1 transformer and sections 50-Ohm cable 
going to each antenna.  That configuration gave me the most usable 
bandwidth on 160m.  The use of the 50-Ohm feed to the antennas also 
allows the use of 50-Ohm cable for the phasing delay-line injected at a 
50-Ohm impedance point instead of the 100-Ohm point when using the 
coaxial transformation method.

After I went through two months of experimenting with how to feed my 
160m verticals, I wondered if I was missing something, or maybe not 
measuring something correctly.  It seems so easy to use a transformer, 
but most past and current magazine and Internet articles on phasing 
verticals are still focused on the use of 75-Ohm coax for matching the 
verticals.

I understand my perceived advantages of a transformer versus coaxial 
matching:
- feeds to each antenna are just equal lengths of 50-Ohm cable, not 
measured electrical lengths of 75-Ohm coax.
- greater usable bandwidth due to not using tuned sections of 75-Ohm coax.
- better matching when using 50-Ohm coax for the delay-line.  (My VSWR 
does not change appreciably when I switch N-S, E, or W.)
But, what I don't understand are the advantages of using 75-Ohm coax for 
matching.

What I am really questioning is the advantages/disadvantages of my using 
a transformer at the feed-point of the phased verticals. My 160m 
verticals have worked out quite well using a transformer, but I am 
always open to changing if there is a better solution.

For Bob's question about 20m verticals, and future 40m verticals, the 
transformer seems to me a logical solution.  You can just switch 
antennas at the end of the 50-Ohm coaxes or use multi-band verticals.

TU es 73,
Bill
N6WS


On 8/13/2019 6:02 AM, W6PH via SCCC wrote:
> Or an odd multiple of 1/4 wavelength 75 ohm cable, i.e. 3/4 or 5/4.  The best theoretical gain is spacing the two verticals 5/8 wave for broadside firing.  The 1/4 wave cable length is too short because of velocity factor.  So you would need two 3/4 wave 75 ohm cables to transform the 50 ohm to 100 ohms at the feed point.
> Kurt W6PH
> In a message dated 8/12/2019 7:52:13 PM Pacific Standard Time, n6vi at socal.rr.com writes:
>
> Hi, Bob.
>
> The most common way I have seen to match your transmitter to paralleled
> 50-Ohm antennas is to feed each antenna with electrical 1/4 wavelengths of
> 75-Ohm coax to the Tee.  That will transform each feed point impedance to
> 100 Ohms, and paralleling two of those gets you back to 50 Ohms.
>
> 73,
>
> Marty N6VI
>
>
> -----Original Message-----
> From: SCCC [mailto:sccc-bounces at contesting.com] On Behalf Of Bob Grubic
> Sent: Monday, August 12, 2019 6:25 PM
> To: Southern California Contest Club
> Subject: [SCCC] Phased verticals
>
> I am considering using two 20-meter phased verticals for some portable
> operations. (Later, two 40-meter verticals.)
>
> Keeping it simple at first, I'd run coax from my rig to a T-connector and
> then through identical, same length pieces of coax to each vertical
> (driving them in phase). I've seen this scenario several times online, but
> the fact that two 50-ohm antennas would be in parallel at the T-connector
> to give you a 25-ohm load (in effect), somehow bothers me.
>
> I've seen an article online suggesting using an UNUN to match the rig's
> coax to the two legs feeding the antennas--essentially replacing the
> T-connector (with a UN-22-25 from CWS). http://www.cwsbytemark.com/  I
> can't find any other discussion of this particular subject online.
>
> Has anyone had any experience with this or thoughts on the subject? I'd
> appreciate hearing about it.
>
> Thanks very much.
>
> 73,
> Bob NC6Q
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