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eHam Forums => Antennas and Towers and more => Topic started by: N4KCE on December 18, 2012, 05:06:24 PM



Title: Help with S9 31 Vertical
Post by: N4KCE on December 18, 2012, 05:06:24 PM
Hello all,
I'm setting up my first HF station. Tomorrow my FT 450D should arrive. I have been preparing the station, antenna, single point ground system. I will have the S9 31 antenna, 80 feet of DX Engineering 400 MAX coax, and YT 450 antenna tuner. At the antenna base I have a 4:1 UNUN from balun designs. Question: When I check the antenna with a MFJ 259 it has the following readings-
x=50 50 ohms and SWR >25. The information from balun designs say that readings may show a dead short or other readings without RF to the antenna. Will my set up be ok when I try and fire up my FT 450D tomorrow?

Thanks
Keith
N4KCE


Title: RE: Help with S9 31 Vertical
Post by: W9FI on December 18, 2012, 07:36:24 PM
Keith, something is wrong with your antenna setup, the feedline, or the antenna analyzer.  I have an old R7 vertical that I've been using for years, and it gets a reasonable SWR (under 1.5:1), both as measured on my MFJ 259 and with an external SWR meter sitting next to the transmitter.  If you measure that balun with an ohmmeter you'll read something very close to zero ohms. That's normal and nothing to worry about.

Are you near a high-power RF source of any sort, like a broadcast band transmitter?  If so that can overload the input of the antenna analyzer and give you bad readings.  If not then let's assume your antenna analyzer is OK, and move to the installation itself.

My next questions would be: do you have the number and length of the recommended radials connected to the base of the antenna?  If you measure where each radial is attached to the base plate, ring, or whatever you're using for the connection, does each radial connection measure zero ohms across it? Do the two connections between the balun's output wires and the antenna also measure zero ohms?

When you measure continuity of the coax, do you see very low resistance connections between the two center pins and between the two shields, like a fraction of an ohm? Is there any reading of any sort between the center pin and the shield? There should be no continuity whatever between the coax shield and the center conductor.

These are the sorts of things I'd check first.  Forgive me if I've mentioned something obvious that you already know about.  It's just that those are the problems I've encountered over the years when I've set up HF verticals.  The 50-ohm analyzer reading tells me that you're probably close to having this antenna set up right.  But assuming your analyzer is working OK and the antenna isn't mounted within a few feet of some big metal object, the high SWR would seem to indicate a high-resistance connection somewhere, or something wrong with the coax, coax connectors, or the radials.

Let us know how you're progressing.  When you find the problem it should turn out to be something simple.

73,  Jim  W9FI


Title: RE: Help with S9 31 Vertical
Post by: K2OWK on December 18, 2012, 09:18:33 PM
Why would you have a 4 to 1 UNUN with a YT-450 tuner? I have a 31 foot S9 antenna with 20 radials on it, and I use a 4 to 1 UNUN because I do not have a wide range tuner on it. The YT-450 should provide enough tuning range without the UNUN. I do not know if this is a problem or how the tuner is reacting to the 4 to 1 UNUN. I would take the UNUN out of the circuit and retest the system with the MFJ-259 and see what it reads.

73s

K2OWK


Title: RE: Help with S9 31 Vertical
Post by: M6GOM on December 19, 2012, 05:58:53 AM
The information from balun designs say that readings may show a dead short or other readings without RF to the antenna.

Not quite. To DC a balun may show a dead short. So when using a multimeter you'd get a short between the outer and inner conductors on the socket. However it doesn't appear as a short to AC which is what RF is.

Using an antenna analyser it will show the same SWR as the transceiver will see.

Doing a full sweep with the antenna analyser from 27MHz upwards connecting with the shortest length of coax between the analyser and the antenna/balun and if you don't see anywhere X=0 or as near as (should be around 31-32MHz without the Balun and around 8MHz with) then you've got a problem.


Title: RE: Help with S9 31 Vertical
Post by: N4KCE on December 19, 2012, 12:00:02 PM
Thanks for all the feedback. I disconnected the feed line and the UNUN. With a short piece of coax I connected the vertical wire and the counter poise. SWR of 1.6 on 7MHZ and SWR of 8.0 on 14MHZ. Guess I can probably tune 20 meters with my tuner.
The antenna instructions said I would need a 4:1 UNUN for multi band operations.

Keith


Title: RE: Help with S9 31 Vertical
Post by: KE6EE on December 19, 2012, 01:47:40 PM
If I'm not mistaken the instructions for that antenna suggest a 1:1 unun for 40M operation and a 4:1 unun for multiband (other than 40M) use.


Title: RE: Help with S9 31 Vertical
Post by: KD2CJJ on December 21, 2012, 12:01:39 PM
I always question whether or not it is better to obtain an impedance match closer to the antenna or further away using a wide range tuner... Of course the results may be the same, but which is more efficient from a loss perspective?

I suspect it would depend on insertion losses introduce by the UNUN itself... BUT I believe that by-itself losses will be relatively low if its high quality... So if that is not a factor (question still) then the SWR over the feedline in theory would be lower with the 4:1 at the antenna using a tuner at the rig over not using a 4:1 UNUN at all using a wide range tuner at the rig.

What are your thoughts?

Why would you have a 4 to 1 UNUN with a YT-450 tuner? I have a 31 foot S9 antenna with 20 radials on it, and I use a 4 to 1 UNUN because I do not have a wide range tuner on it. The YT-450 should provide enough tuning range without the UNUN. I do not know if this is a problem or how the tuner is reacting to the 4 to 1 UNUN. I would take the UNUN out of the circuit and retest the system with the MFJ-259 and see what it reads.

73s

K2OWK


Title: RE: Help with S9 31 Vertical
Post by: N8CMQ on December 22, 2012, 04:43:36 PM
I'm confused, are you checking SWR before or after the tuner?
If the tuner is out of circuit, then I expect SWR to be all over
the place, depending on frequency. If the tuner is in the circuit,
you should have a perfect match.
However, the tuner needs to be active and tuned, to work.


Title: RE: Help with S9 31 Vertical
Post by: K3VAT on December 22, 2012, 05:51:12 PM
...
My next questions would be: do you have the number and length of the recommended radials connected to the base of the antenna?  ...  73,  Jim  W9FI

Until this question is fully answered we don't have an understanding of the full antenna system setup.  Discussion re: baluns/ununs are, IMHO, important, but not vital as W9FI correctly pointed out.  What's the second half of the antenna?
GL, 73, Rich, K3VAT