Two Good Days Spent with Quads
 

My friend had a 4-element 2m quad with dangerously high VSWR. Somebody gave
it to him (which I guess was the first sign). Yesterday, he brought it by
for me to check it out.

I don't have an analyzer (yet) for 2m, but careful VSWR measurements made it
look like the antenna was resonant out-of-band low. We carefully measured
the driven element length and compared it to the calculated length from the
ARRL Antenna Handbook. It was about 1.3 inches too long, so we stripped out
the spreaders, redrilled and reassembled with a shorter driven element.
Voila! 2.1:1 to 2.4:1 across the bad, with the low point in-band. He went
on his way, happy.

Last night I studied a little and saw that the quad loop is normally
resonant with about 100 ohms at the feedpoint. I used some # 12 wire to
build a 222 MHz quad loop today and, sure enough, 2.1:1 was the best I could
do. I remembered the use of a quarter wave section of line as a matching
transformer and decided a transformation of 50 -- 75 -- 100 was too easy
not to try. At 66% velocity factor, that's just over 23 cm of RG-59.

It worked perfectly. Resulting VSWR was better than 1.4:1 from 222 to 225.
From my location south of San Diego, I brought up several distant repeaters
(Hollywood Hills, Catalina) and even worked a guy in Santa Barbara through a
repeater at his end, over 200 miles away. All this with 5 watts to my
humble quad loop on a 9-foot plastic stick tied off to the patio cover.

I understand that a quad loop has a pattern about that of a dipole and a
quad array will deliver useful gain with just one parasitic element. Dunno
if the parasitic should best be a reflector or a director but I'll find out.
I built a reflector but haven't tested it yet in conjuction with the
exisiting loop. That's next.

I love this hobby!

"Sal"
(KD6VKW)

Two Good Days Spent with Quads
 

On Fri, 10 Aug 2007 22:18:19 -0700, "Sal M. Onella"
wrote:

I love this hobby!

Hi Sal,

Good story.

73's
Richard Clark, KB7QHC

Two Good Days Spent with Quads
 

On Fri, 10 Aug 2007 22:18:19 -0700, "Sal M. Onella"
wrote:

My friend had a 4-element 2m quad with dangerously high VSWR. Somebody gave
it to him (which I guess was the first sign). Yesterday, he brought it by
for me to check it out.


I love this hobby!

"Sal"
(KD6VKW)

Don't overlook that you can parallel two quads to get to 50 ohms as
well!

There is no end to the fun with VHF Quads. About any kind of sticks,
wire and tape will get you going. Don't forget to keep notes, they are
very useful as the learning accelerates.

John Ferrell W8CCW
"Life is easier if you learn to
plow around the stumps"

Two Good Days Spent with Quads
 

"John Ferrell" wrote in message
...



Don't overlook that you can parallel two quads to get to 50 ohms as
well!


OK, I took a mental excursion in that direction. My first thought is to use
two runs of RG-62 93-ohm computer drop cable off a t-connector. This goes
against my grain -- I've always hated using any t-connectors in a matched
system -- but I guess the match will be maintained.

My second thought is to literally parallel them at the end of a hunk of
50-ohm cable. That feed would need to be crossed over, I think, so the
fields would be additive. Easy enough to test it both ways, I suppose. If
crossover is needed, what would the pattern look like without it? Hm-m-m-m
.... near-field cancellation and no pattern? Pattern rotation?

Of course I will be trying this next idea even if no newsgroup answer is
forthcoming: What happens if I tap off quad #1 on the side _opposite_
where I'm feeding it and connect quad #2 there? Wouldn't this additional
load reflect back to feed #1 and lower its impedance toward 50 ohms? I
don't know what feed #2 would be. Perhaps a jury-rig parallel line
calculated to be 100 ohms would do it. (# 10 AWG wires on 5 mm centers would
do it.) Phasing will be an issue.
[I probably don't have a suitable test environment to tell success from
failure.]

73,
"Sal"

Two Good Days Spent with Quads
 

[After sending this, I never saw it posted so I re-sent. Sorry if it's a
dupe in your newsreader.]

"John Ferrell" wrote in message
...



Don't overlook that you can parallel two quads to get to 50 ohms as
well!


OK, I took a mental excursion in that direction. My first thought is to use
two runs of RG-62 93-ohm computer drop cable off a t-connector. This goes
against my grain -- I've always hated using any t-connectors in a matched
system -- but I guess the match will be maintained.

My second thought is to literally parallel them at the end of a hunk of
50-ohm cable. That feed would need to be crossed over, I think, so the
fields would be additive. Easy enough to test it both ways, I suppose. If
crossover is needed, what would the pattern look like without it? Hm-m-m-m
.... near-field cancellation and no pattern? Pattern rotation?

Of course I will be trying this next idea even if no newsgroup answer is
forthcoming: What happens if I tap off quad #1 on the side _opposite_
where I'm feeding it and connect quad #2 there? Wouldn't this additional
load reflect back to feed #1 and lower its impedance toward 50 ohms? I
don't know what feed #2 would be. Perhaps a jury-rig parallel line
calculated to be 100 ohms would do it. (# 10 AWG wires on 5 mm centers would
do it.) Phasing will be an issue.
[I probably don't have a suitable test environment to tell success from
failure.]

73,
"Sal"

Two Good Days Spent with Quads
 

Of course I will be trying this next idea even if no newsgroup answer is
forthcoming: What happens if I tap off quad #1 on the side _opposite_
where I'm feeding it and connect quad #2 there? Wouldn't this additional
load reflect back to feed #1 and lower its impedance toward 50 ohms? I
don't know what feed #2 would be. Perhaps a jury-rig parallel line
calculated to be 100 ohms would do it. (# 10 AWG wires on 5 mm centers would
do it.) Phasing will be an issue.
[I probably don't have a suitable test environment to tell success from
failure.]

73,
"Sal"


It is easier and cheaper to do phasing/matching harnesses with open
wire. Make it, don't buy it. Considering that a 1/4 wave is only about
19 inches you can make experiments with whatever wire is handy using
popsicle sticks ("craft sticks" at the craft store) and masking
tapefor the spacers.

Make a field strength meter with a diode and dipole connected to a
multi meter. space it about 30 feet in front of the quad. While
transmitting verify the elements are all working by touching each
element with a screwdriver.

Operate the transmitter at lowest possible power.

Too much fancy equipment gets distracting.

John Ferrell W8CCW
"Life is easier if you learn to
plow around the stumps"

Two Good Days Spent with Quads
 

"Sal M. Onella" wrote in message
...

"John Ferrell" wrote in message
...



Don't overlook that you can parallel two quads to get to 50 ohms as
well!


OK, I took a mental excursion in that direction. My first thought is to
use
two runs of RG-62 93-ohm computer drop cable off a t-connector. This goes
against my grain -- I've always hated using any t-connectors in a matched
system -- but I guess the match will be maintained.

My second thought is to literally parallel them at the end of a hunk of
50-ohm cable. That feed would need to be crossed over, I think, so the
fields would be additive. Easy enough to test it both ways, I suppose.
If
crossover is needed, what would the pattern look like without it?
Hm-m-m-m
... near-field cancellation and no pattern? Pattern rotation?

Of course I will be trying this next idea even if no newsgroup answer is
forthcoming: What happens if I tap off quad #1 on the side _opposite_
where I'm feeding it and connect quad #2 there? Wouldn't this additional
load reflect back to feed #1 and lower its impedance toward 50 ohms? I
don't know what feed #2 would be. Perhaps a jury-rig parallel line
calculated to be 100 ohms would do it. (# 10 AWG wires on 5 mm centers
would
do it.) Phasing will be an issue.
[I probably don't have a suitable test environment to tell success from
failure.]

73,
"Sal"



Stacking two 100 ohm impedance quads is electrically about as easy as it
gets. An electrical 1/4wl of any good quality coax from each antenna to a T.
50 ohm cable to the shack.


Jimmie.

Two Good Days Spent with Quads
 

"Jimmie D" wrote in message
...


Stacking two 100 ohm impedance quads is electrically about as easy as it
gets. An electrical 1/4wl of any good quality coax from each antenna to a
T.
50 ohm cable to the shack.

Thanks. I would've thought it needed to be 1/4w/l of 75-ohm cable, but
I'll try it.

Two Good Days Spent with Quads
 

"Sal M. Onella" wrote in
:


"Jimmie D" wrote in message
...


Stacking two 100 ohm impedance quads is electrically about as easy as
it gets. An electrical 1/4wl of any good quality coax from each
antenna to a
T.
50 ohm cable to the shack.

Thanks. I would've thought it needed to be 1/4w/l of 75-ohm cable,
but
I'll try it.

You are right to question to advice Sal.

Of course with a 1/4wl with VSWR=2, the Zo does matter.

However, Jimmie might have meant each leg to be a 1/2wl (electrical)...
close wasn't it! In that case, Zo isn't critical.

Owen

Two Good Days Spent with Quads
 

"Owen Duffy" wrote in message
...
"Sal M. Onella" wrote in
:


"Jimmie D" wrote in message
...


Stacking two 100 ohm impedance quads is electrically about as easy as
it gets. An electrical 1/4wl of any good quality coax from each
antenna to a
T.
50 ohm cable to the shack.

Thanks. I would've thought it needed to be 1/4w/l of 75-ohm cable,
but
I'll try it.

You are right to question to advice Sal.

Of course with a 1/4wl with VSWR=2, the Zo does matter.

However, Jimmie might have meant each leg to be a 1/2wl (electrical)...
close wasn't it! In that case, Zo isn't critical.

Owen

Owen you are a good mind reader, sorry about the typo, should have been 1/2
wl.


Jimmie