G5RV and if they need a balun???
maxpowervk
ladderline. At the end of the ladder line I have a coax choke balun and
that joins into a run of about 20 feet of 50 ohm coax which runs to my
HF radio.The radio has an inbuilt ATU. The antenna loads up on
80,40,20,15 and 10m ok. I have been listening to conversations on 40m
lately where people are suggesting using a 4:1 balun at the end of the
ladderline. Has anybody on this forum had any experience using a 4:1
balun on a G5RV and what effect it has.
Cheers,
Max
Owen Duffy
news:1167951888.2...@42g2000cwt.googlegroups.com:
Max,
I wrote an article at http://www.vk1od.net/G5RV/index.htm analysing G5RVs
with a range of common variant feed arrangements.
The impact of the 4:1 balun will mainly be a change in the loss on the
coax line section, and a change to the load impedance presented to the
ATU that may change ATU losses or even the ability to match up with your
particular cable lengths (a greater risk with internal ATUs which have
more limited range). A G5RV can perhaps be used without an ATU on just
one band, 20m. The 4:1 balun should ensure that it needs an ATU on all
bands.
I have just calculated the loss in 6m of RG58C/U feedline on 80, 40, and
20 using a 1:1 balun and 4:1 balun in the models used for the article.
The 4:1 balun does give an improvement on 80m (0.13dB vs 0.7dB), but is
worse on 40m (2.0dB vs 1.0dB) and 20m (1.2dB vs 0.4dB).
Did the on air discussion disclose why it was supposed to work better?
Did it offer some conlusive measurement proof that it is better?
If you are interested in optimising a G5RV, you may find the article
http://www.vk1od.net/G5RV/optimising.htm of interest.
Owen
maxpowervk
I have just finished reading your notes on optimizing the G5RV. Between
the choke balun and the radio I use RG213. I found it very interesting
reading and I have definitely learnt some things. I am going to pull it
down and tune the ladderline length. That is something that I should
have thought of when I originally built the antenna. When tuning the
ladderline length, what is the best way to go about it? Stringing it up
vertically, I would assume to be the best way to do it.
Also, I use a choke balun made from RG213 coax, but I still hear other
people saying to use a 4:1 balun. If the impedance at the end of the
ladderline is around 90 ohms ( at 14.150 Mhz), the 4:1 balun would
bring it down to about 23 ohms. I don't know if there is any advantage
to that. As I said in my original post, I only use the G5RV on 40 and
80 metres, so whether a 4:1 balun would be better I don't know.
All the best
Max
Owen Duffy
news:1168409852.6...@k58g2000hse.googlegroups.com:
> Hello Owen,
> I have just finished reading your notes on optimizing the G5RV. Between
> the choke balun and the radio I use RG213. I found it very interesting
I take it you mean a coil of several turns of RG213. It is unlikely that
at low HF you have enough choking reactance to be very effective.
> reading and I have definitely learnt some things. I am going to pull it
> down and tune the ladderline length. That is something that I should
One of the greatest variables is the velocity factor of the open wire
line, and people seem to frequently ignore it, then experience problems
in tuning the system. Additionally, there are loss implications and the
efficiency graph in the article illustrates the issue.
I listened to a guy on 20m describing his G5RV using TV ribbon cut to the
length in Louis' article but defied tuning on 20m (which should be the
easiest band to tune). TV ribbon has a velocity factor somewhere round
0.7 to 0.85 depending on the construction. His ribbon section, although
cut to the quarter inch to 29' something, was probably up to 6' too long.
It is a common mistake.
> have thought of when I originally built the antenna. When tuning the
> ladderline length, what is the best way to go about it? Stringing it up
> vertically, I would assume to be the best way to do it.
String it up anywhere clear of other conducting material and other
dielectrics than air. You could use fishing line to make suspension ties
to support it for your test.
> Also, I use a choke balun made from RG213 coax, but I still hear other
> people saying to use a 4:1 balun. If the impedance at the end of the
Ask them why the 4:1 works better, not a count of QSL cards, or signal
reports, but the reason why it works better.
> ladderline is around 90 ohms ( at 14.150 Mhz), the 4:1 balun would
> bring it down to about 23 ohms. I don't know if there is any advantage
> to that. As I said in my original post, I only use the G5RV on 40 and
You could calculate the coax load end VSWR for each scenario, it is 1.8
vs 2.2... but what does that tell you? I worked the loss out for you (on
20m) and it was an additional 0.8dB, meaning 83% of the EIRP using a 1:1
balun. Chucking away 17% of your power doesn't seem like an improvement
to me. The 4:1 balun does not make an across the board improvement.
> 80 metres, so whether a 4:1 balun would be better I don't know.
If you optimise the antenna along the lines suggested in the article so
as to ensure that the peak in efficiency around 80m is in the band where
it is usable, then you will have done well.
Less, and better coax is better.
A better choke balun might be worth the effort and expenditure. Last
choke balun I made used about $16 of cores from Jaycar and half a metre
of cable, it need not cost a heap.
> All the best
> Max
Cheers
Owen
>
>
maxpowervk
The choke balun I made is of 20 feet of RG213 coax wound tightly on a
100mm diameter PVC pipe. I sourced the design from hamuniverse.com.
When I first installed it there was a noticable difference in the SWR
readings on some of the bands. I didn't take any notes at the time so I
can't remember exactly but when I tune the ladderline and set the G5RV
up again I will take readings with and without the choke balun.
I am interested in the one you are talking about. I assume it is made
up of ferrite beads placed on the coax. How many were used?
I know there are alot better antennas for me to use on 40m and 80m than
the G5RV but I am enjoying experimenting with it and learning alot
along the way.
Next I may experiment with a 40m and 80m dipole fed from the one coax
and see how I go.
All the best,
Max
Owen Duffy
news:1168471132.5...@o58g2000hsb.googlegroups.com:
> Thanks again Owen for replying to my posting.
> The choke balun I made is of 20 feet of RG213 coax wound tightly on a
> 100mm diameter PVC pipe. I sourced the design from hamuniverse.com.
> When I first installed it there was a noticable difference in the SWR
> readings on some of the bands. I didn't take any notes at the time so I
> can't remember exactly but when I tune the ladderline and set the G5RV
> up again I will take readings with and without the choke balun.
There is argument about whether a balun is desirable on a G5RV. Louis
Varney's first article recommended a balun, then his next was against
such. His reasons for not recommending a balun in his second article
reflected the lack of understanding of current or choke baluns in those
days, and IMHO is wrong. There is no doubt the antenna is not grounded on
one side whereas the transmitter typically is. In that scenario, a device
that facilitates the transition from the unbalanced transmitter to the
"balanced" antenna is warranted, and that device is a balun. In most
cases a current balun or choke balun is probably the better choice.
Will it "work" without it? Of course it will.... but what does "work"
mean?
> I am interested in the one you are talking about. I assume it is made
> up of ferrite beads placed on the coax. How many were used?
Yes it is. I measured the characteristics of Jaycar's LF1258 cores and
the results are at http://www.vk1od.net/balun/index.htm. My suggestion is
that for a G5RV at the transition from open wire feeder to coax, that you
use at least 18 of these cores, 24 wouldn't go astray.
I use a balun made with these cores on my 20m dipole. The slighly over
half wave dipole is fed with a "tuned" length of RG6/U for a VSWR < 1.1.
The balun is a bunch of these cores slipped over the RG6 (with the jacket
removed), and the whole feedline (20m of it, including the balun) is
slipped inside 13mm irrigation tube to protect it from the cockies.
Cockies eat vinyl jackets, but don't seem interested in polyethylene
irrigation tube. Anyway, the antenna system has about $15 of parts in the
balun, about $8 of feedline cost, about $6 of irrigation tube, about $5
for connectors, and it has performance as good as using RG213, doesn't
require an ATU and allows the PA to develop rated power into the load
presented.
Now some folk insist that if the dipole isn't resonant, it "won't work
any good". my article "The importance (or not) of being resonant" at
http://www.vk1od.net/iobr/ canvasses that issue.
> I know there are alot better antennas for me to use on 40m and 80m than
> the G5RV but I am enjoying experimenting with it and learning alot
> along the way.
That is what the hobby is (or was) about.
You have hit on an important issue, it is what suits your own situation,
and compromises are almost always necessary. That is why someone else
cannot insist on what is best for your situation.
> Next I may experiment with a 40m and 80m dipole fed from the one coax
> and see how I go.
I think you may be referring to a fan dipole, certainly viable. Have fun
learning.
> All the best,
> Max
>
>
Cheers
Owen