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Author Topic: SteppIR BigIR Installation Early Results - Any Advice?  (Read 2611 times)
W4LI
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« on: April 28, 2013, 05:17:53 AM »

I just completed the install of the BigIR with 80 Meter coil.  I used the DX engineering base plate. About 50 radials from 25 feet (shortest) to 70 feet -- 40 feet typical.

The base of the EHU is about 8" above ground level, so tight the boot hits the radial plate (slightly).  The coax is buried with the control cables a couple inches below ground in SCH 40 pipe.  Coax and control lines are choked with a few turns through ferrite on entry at the shack. 

So far, the match results are not good.  Results are the same without the supplied balun/choke. I haven't reprogrammed the lengths yet, but want to see if that's the likely solution.

80 Meters: 
1.5 or 1.6:1, but 175KC below the stated frequency (not bad, just needs some adjustment).

40 Meters:
2.2:1 and it seems flat across the band, regardless of where the SDA100 indicates in relationship to transmit frequency.

30 Meters:
3:1 or worse, didn't investigate much

20 Meters:
Near perfect match everywhere

17 Meters:
Roughly 2:1

15 Meters:
3:1, consistent across the band

12 Meters
3:1, consistent across the band

10 Meters
Over 3:1 across, didn't explore as much yet.

As a test, connected a dummy load to the coax at the antenna feed point, resulting in roughly 1:1 on all bands --
showing something didn't happen in the coax setup, connectors good, etc. 

I haven't had much time yet, but seems to generally work on 80/40/20, but not
necessarily optimally. I had about half the radials installed yesterday and saw
essentially the same results.

Any thoughts on next steps or suggestions will be greatly appreciated. When I use create/modify on the SDA100, DRV obviously controls element length.  Does one of the others control the 80M coil tap and/or bypass the 80M coil?

Also, special thanks to Mark, K8GY who helped immensely with the installation process.  I'm really looking forward to having the fully tuned and operating.

Thanks in advance,
Dan, W4LI
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W4LI - Dan Hoogterp
K3VAT
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Posts: 709




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« Reply #1 on: April 28, 2013, 05:49:05 AM »

The factory defaults are only one approximation.  Your setup is unique, so you'll need to:
1. tell the controller that you have the 80M coil (appears that you have done this)
2. in "create modify" use a combination of the "coarse up/down" and the "fine up/down" to tune your antenna.

After modification, if the SWRs are NOT nominal, then you'll have a concern.

GL, 73, Rich, K3VAT
« Last Edit: April 28, 2013, 05:56:04 AM by K3VAT » Logged
K2MK
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Posts: 393




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« Reply #2 on: April 28, 2013, 06:36:05 AM »

I've had a BigIR with 80 meter coil for about 6 years. As K3VAT indicated you have to use create/modify as the factory settings are seldom reliable for a vertical antenna. Your ground conditions and nearby objects strongly affect the element length.

Next, it is very important that the frequency on the controller match your transmit frequency. Do not get in the habit of moving the controller frequency to improve SWR. This is especially true on 80 meters where the coil will change its tap position at several different frequencies. The best arrangement is to utilize transceiver tracking so that the SteppIR controller follows your transmit frequency.

Lastly, with the 80 meter coil SteppIR recommends that you use 3/4 wave mode. It's only active on 15 through 6 meters but it will usually improve your SWR on those bands.

73,
Mike K2MK

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K3GM
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« Reply #3 on: April 28, 2013, 10:17:42 AM »

1) I use a 2" wide piece of copper ribbon to connect the stud on the coil to the DX Engineering radial plate. I trim it to fit it in the space on the coil body, and connect it to several screws on the radial plate.

2) If you use an UnUn, do not place it near the coil.  My first attempt with the SteppIR UnUn, I RTV'd it to the coil housing.  Really bad results!

3) if you have an extensive radial field, try an antenna analyzer and measure the feedpoint impedance.  Mine was sufficiently low that I needed a 1.56:1 transformer at the feedpoint.
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N4FBW
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« Reply #4 on: April 28, 2013, 10:05:00 PM »

If you haven't already done so, join and post your question to the Steppir Group on Yahoo; lot's of helpful folks on this group:

http://groups.yahoo.com/group/SteppIR/

Rick, N4FBW
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KH6DC
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« Reply #5 on: April 29, 2013, 04:01:34 PM »

It's a great antenna, had one for about 4 years then sold it when I moved into a HOA community.  Like others said, you need to go into the setup of the SDA 100 Controller and add the 80m coil.  Your SWR should decrease to almost flat and increase performance.  Had mine on a DX Engineering Tilt Base but because of the increase height, it screwed the SWR.  I removed the tilt base and dropped it per STEPPIR's instructions which resulted in flat SWR across the bands from 6-80m.  I even worked 160m!
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73 and Aloha,
de Delwyn, KH6DC
W4LI
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« Reply #6 on: May 13, 2013, 11:24:52 AM »

First, thanks for all the helpful responses.  Sorry about the lag time...

I did manage to tune the SDA100 through 'create, modify' to get roughly 1.5 across 80M, and using 3/4 mode, tweaked to similar or better results on higher frequency bands (above 20M).  Without 3/4 mode, I can't get a decent match on the higher frequency bands.

However, I still see about 2.3:1, at best, on 40M.  The antenna appears to work reasonably, albeit the higher than expected SWR.

I'm in South Florida, near salt water, with 48 radials averaging 50 feet.  The other factor that may be affecting SWR is an aluminum frame for a screen enclosure around a pool - about 25 feet away to one side -- probably 20 feet wide, 15 feet high, viewed from the antenna at that point.

I'm mainly trying to confirm that this is within expected outcomes and that nothing is done incorrectly or broken.  I'm planning an amp change soon, so it does force me into amps that handle that level of mismatch, either by output tuning or antenna tuner.

I don't have an analyzer, but this may be a good time to get one.  I'll post this in the Steppir yahoo group as well.

Thanks again for comments to date.  Any further thoughts or suggestions would be appreciated. 

73, Dan Hoogterp, W4LI
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W4LI - Dan Hoogterp
K3VAT
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« Reply #7 on: May 13, 2013, 03:34:25 PM »

First, thanks for all the helpful responses.  Sorry about the lag time...

I did manage to tune the SDA100 through 'create, modify' to get roughly 1.5 across 80M, and using 3/4 mode, tweaked to similar or better results on higher frequency bands (above 20M).  Without 3/4 mode, I can't get a decent match on the higher frequency bands.

However, I still see about 2.3:1, at best, on 40M.  The antenna appears to work reasonably, albeit the higher than expected SWR.

I'm in South Florida, near salt water, with 48 radials averaging 50 feet.  The other factor that may be affecting SWR is an aluminum frame for a screen enclosure around a pool - about 25 feet away to one side -- probably 20 feet wide, 15 feet high, viewed from the antenna at that point.

I'm mainly trying to confirm that this is within expected outcomes and that nothing is done incorrectly or broken.  I'm planning an amp change soon, so it does force me into amps that handle that level of mismatch, either by output tuning or antenna tuner.

I don't have an analyzer, but this may be a good time to get one.  I'll post this in the Steppir yahoo group as well.

Thanks again for comments to date.  Any further thoughts or suggestions would be appreciated. 

73, Dan Hoogterp, W4LI


OK Dan, we're into phase II of troubleshooting (now that you have used the create/modify to obtain your lowest SWR).

Three items come to mind:
1.  the aluminum frame for the pool screen is an influence (as that much metal in the near field will cause interaction); however, whether it is a problem it is hard to say without more tests.  The Steppir should be able to 'compensate' for this and produce a decent (<1.5:1) match.  Are there any close by buried electrical service lines or gas lines, etc. that you know of?
2.  how long is the coax run from the antenna feed point to the xcvr?  what kind of coax are you running?  is it buried? age?
3.  does the SWR change between tuning (with lower power) and full power?

Yes, an analyzer that provides a graphic readout, like the RigExperts (from ArraySolutions.Com) is often very helpful in cases such as this and I recommend that you get something to assist your troubleshooting.

GL, 73, Rich, K3VAT
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W4LI
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« Reply #8 on: May 13, 2013, 05:03:02 PM »


OK Dan, we're into phase II of troubleshooting (now that you have used the create/modify to obtain your lowest SWR).

Three items come to mind:
1.  the aluminum frame for the pool screen is an influence (as that much metal in the near field will cause interaction); however, whether it is a problem it is hard to say without more tests.  The Steppir should be able to 'compensate' for this and produce a decent (<1.5:1) match.  Are there any close by buried electrical service lines or gas lines, etc. that you know of?
2.  how long is the coax run from the antenna feed point to the xcvr?  what kind of coax are you running?  is it buried? age?
3.  does the SWR change between tuning (with lower power) and full power?

Yes, an analyzer that provides a graphic readout, like the RigExperts (from ArraySolutions.Com) is often very helpful in cases such as this and I recommend that you get something to assist your troubleshooting.

GL, 73, Rich, K3VAT


Rich,

Thanks for the quick response. 

As to the aluminum frame, I would also be surprised if it is that strong of an effect that it can't be tuned out from a match perspective.  It probably sweeps 30 degrees at 25 feet away.  Possible, but seems unlikely to be that strong - and then mostly on 40.

The house has underground propane, and given the tank location and the antenna, it shouldn't get within 30-40 feet (worst case routing) of the antenna.  Most likely it doesn't get within 50 feet+, but likely reaches in one end of the radial field (radials on the surface with lawn staples).  The tank is a long way in front of the house, the antenna side/back.

The electric main comes into the opposite side of the house, so that it seems unlikely power runs underground here -- but I can't be certain there isn't something.  The house has some underground wiring for landscape lights, though they are no longer functional in this area - and nothing apparent near the antenna/radial field.

The coax is in electrical sch 40 conduit, along with the two control wires. It is buried a few inches for the first 30 feet, and then at ground level behind bushes for the remaining 30 feet.  Total coax is less than 70 feet.  It is new 9913.

The SWR picks up between about zero and 25 watts drive on my 7600 -- it doesn't change between 25 watts and 100 on the exciter, or even 1000 with the AL-80B cross-needle meter, which reads the same.  I recall the 7600 has always done this, needing moderate drive for an SWR reading, even with different qth/antennas.  I don't think it reads correctly at lower drive.   Maybe I'm wrong.

The coax is wound a few times through a 1+" ferrite on entry to the shack, as a preventative.  I have a good ferrite collection, so most other signal/control cables are similarly choked in the shack.  The 1:1 Steppir Balun at the feed point made no difference (so I am not using it).  Everything has been stable in operation, even with the AMP - giving no indication of RFI in the shack, but still a possibility as well.

Any further thoughts would be appreciated.  I'm looking into the RigExperts analyzer.  I'd looked at it before, but never had a real and present need.  Maybe now I do.

73, Dan, W4LI
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W4LI - Dan Hoogterp
K3GM
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« Reply #9 on: May 13, 2013, 06:40:44 PM »

Consider this, Dan.  By your description, you have a fairly extensive radial field.  A big radial field can cause a feedpoint impedance as low as 35-37 ohms.  So you have a 50 ohm tramsmission line connected to a 37 ohm amtenna; a built in mismatch that no lengthening or shortening will fix.  This is where a transformer may help.  As an experiment, try disconnecting the antenna from the radial field and use only your lightning ground rod as your return path.  Your feedpoint impedance should now be 50 ohms or a bit higher due to ground loss and you should now see a better match across the bands.  Unfortunately, you now have a very ineffecient radiator.

You didn't mention what you were using to establish a VSWR reading, but I feel that the onboard rig meters put you in the ballpark at best.  An antenna analyzer or forward and reflected power readings from a Bird will give you accurate readings.
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W4LI
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« Reply #10 on: May 16, 2013, 05:58:52 AM »

Consider this, Dan.  By your description, you have a fairly extensive radial field.  A big radial field can cause a feedpoint impedance as low as 35-37 ohms.  So you have a 50 ohm tramsmission line connected to a 37 ohm amtenna; a built in mismatch that no lengthening or shortening will fix.  This is where a transformer may help.  As an experiment, try disconnecting the antenna from the radial field and use only your lightning ground rod as your return path.  Your feedpoint impedance should now be 50 ohms or a bit higher due to ground loss and you should now see a better match across the bands.  Unfortunately, you now have a very ineffecient radiator.

You didn't mention what you were using to establish a VSWR reading, but I feel that the onboard rig meters put you in the ballpark at best.  An antenna analyzer or forward and reflected power readings from a Bird will give you accurate readings.

Thanks, I'll give that something similar this weekend.  I will just run the ground connection to a couple of specific radials, rather than the radial plate.  I'll post the results.

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W4LI - Dan Hoogterp
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