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Author Topic: 17th Floor Counterpoise for Vertical Whip  (Read 1341 times)
W3NCL
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Posts: 13




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« on: November 26, 2017, 07:20:33 PM »

Good evening!

So, for starters, my setup is as follows:

QTH: 17th floor of a 22-floor apartment building
Radio: Xiegu X-108G (20W)
Power: 12v from marine deep cycle battery
Antenna: MFJ-1899T multi-band telescoping whip in a 2' PVC pipe holder/mast sitting in a xmas tree stand

I am, frankly, a bit lost when it comes to counterpoise, radials, and ground as it applies to me because most write-ups deal with operating on literal ground (as in a grass field) rather than a balcony floor 170 or so feet up, and I don't operate from a real shack with a ground bus, etc.

What I'd like to do is to see if I can get the whip to work on 80m, which it's supposed to. Can I get away with attaching a 54' length of wire (90% of quarter-wave [234/3.9MHz - my desired center frequency of the 80/75m General phone band]) to the outside part of the SO-239 connector and then "snaking" the wire back and forth in parallel runs along the balcony floor?

I do have an MFJ-9201 tuner, but I'd like to at least get a decent starting point rather than trying to tune down an SWR of 1 bajillion:1. Am I missing something before I set this up or am I simply wasting my time?

And please note that while I appreciate the sub-optimal type of antenna choice and the merits of running a full half-wave wire from my balcony to the roof of the next building or the top of a 120-foot-far-away tree I'm not keen on having a stern conversation with my HOA. I need to keep my antenna firmly contained within the confines of my 24' long balcony as I'm already lighting incense while sacrificing young animals to my wife in daily gratitude for putting up with me, so I don't want want to propose turning our living room ceiling into a magnet wire cobweb. ;-)

Thank you, and I apologize in advance for the potential idiocy of my question.

73,

Nico
W3NCL
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WB6BYU
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Posts: 17182




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« Reply #1 on: November 26, 2017, 08:40:31 PM »

Before you try a wire counterpoise (which likely would radiate more power than the antenna
itself), see if there is an alternative.

Do you have a metal railing on the balcony?  Metal door or window frames?  Metal plumbing
or heating ducts nearby?

I used an 80m mobile whip sticking horizontally out an upper window once, with the metal
window frames for a ground, a they were connected together throughout the whole building.

The secret is to find some metal connection that is common to the building, so it is large
with respect to a quarter wave (or at least to the antenna itself.)  You may have to experiment
and try different things.

So, yes, you would connect a wire to the antenna ground connector somehow.  For a BNC
connector, I've often just wrapped a wire around the the jack before plugging the antenna in,
or you can find an appropriate sized solder lug to slip on it.  (If it doesn't make good contact
you may have to bend it a bit.)

Then the wire - as short as you reasonably can - would connect to your ground system.  That
may take some creativity as well:  I've wrapped wires around radiator pipes and clamped them
to water faucets (back when pipes were metal).  A sheet metal screw and a toothed lock washer
may help for some metal objects (at least where you aren't worried about contents leaking out)
or a hose clamp around a deck railing, with the paint scraped away in an inconspicuous spot
if needed.


If you can't manage a ground that way, then you can use a counterpoise.  The most effective
way would be to let the wire hang down off the side of your balcony where it won't run past
the windows below you and be noticed.  (A fishing reel may be handy for extending and retracting
the wire when needed.)

Otherwise I'd run it around the inside of your apartment.  The more you bend it, the more it will
detune the radial, but it sounds like the antenna has some room for adjustment.  But try to run
it around as much of the perimeter as possible (it can pass up and over door frames, etc.) to use
up the length, rather than running it back and forth in a small area.


I would expect that the antenna will have a very narrow operating bandwidth, and small variations
in the vicinity of the antenna may detune it.  We had that problem with an 80m "Hamstick" dipole,
were a tree branch blowing in the wind 5' away would cause SWR to vary up to 3 : 1.  You may be
best off in that case using the tuner for fine tuning, as it would allow you to be far enough away
that you wouldn't change the tuning when you moved.


And if you are trying to work stations out to a couple hundred miles, you may find that sticking the
antenna horizontally off the edge of the balcony works better, as I did with the mobile whip.
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KF4ZGZ
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Posts: 40


WWW

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« Reply #2 on: November 27, 2017, 02:28:30 AM »

I think I would figure out a way to conceal an endfed running down the wall.
That's some serious height and would work well.

Matt
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W3NCL
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Posts: 13




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« Reply #3 on: November 27, 2017, 05:16:11 AM »

@WB6BYU - Why would the counterpoise radiate? My reason for keeping it at 10% below quarter-wave was to prevent just that, based on my reading on the topic. Or is this a function of being on a 17th floor balcony and the 10% thing applies only when closer to actual ground? That being said, I do have two large balcony sliding doors I could try to screw one wire each to. Certainly worth a try. But I would love to know the rationale behind doing that vs counterpoise wire. Thanks!

@KF4ZGZ - You know, I'm seriously close to doing just that. I'm thinking of the EFT-10/20/40 EndFedz Trailrated. It's apparently quite stealthy with black #26 wire, and with a fishing weight on the bottom...who knows. If I do go that way I may just sell the MFJ-1899T at an upcoming hamfest. Maybe even my MFJ-2240 mini-dipole. Thanks!
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W5DXP
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« Reply #4 on: November 27, 2017, 06:21:42 AM »

Why would the counterpoise radiate?

There is nothing to keep a single wire counterpoise from radiating. The way to keep a single wire carrying RF energy from radiating is to cancel the fields surrounding the wire which takes another wire with a field of equal magnitude and opposite phase. It takes at least two similar symmetrical opposing radials to cancel most of the far field radiation from the radial system. Field cancellation also occurs in two wire transmission lines carrying differential currents.

If you can hang a 66 ft. end fed antenna from your balcony, why can't you hang a 66 ft. counterpoise?
« Last Edit: November 27, 2017, 06:26:17 AM by W5DXP » Logged
W3NCL
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Posts: 13




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« Reply #5 on: November 27, 2017, 07:04:39 AM »

@W5DXP - OK, it was just my understanding from all the other articles I've read that you don't want the counterpoise to radiate - just to provide, well, a counterpoise for the actual radiating element, i.e. the antenna itself.

And true, the purpose of the wire I drop is, indeed, irrelevant. I just want to make sure that if I do that I get the best bang for the drop. So would I likely get better performance putting the MFJ-1899T near the corner of the balcony and dropping the counterpoise down the balcony or dropping an end-fed half-wave that doesn't need a counterpoise?

Thanks!
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WB6BYU
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Posts: 17182




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« Reply #6 on: November 27, 2017, 08:17:44 AM »

Quote from: W3NCL

...So would I likely get better performance putting the MFJ-1899T near the corner of the balcony and dropping the counterpoise down the balcony or dropping an end-fed half-wave that doesn't need a counterpoise?




In that case, the MFJ-1899T might make an adequate counterpoise for the vertical wire...


And clearly we need to find you some better reading material!


The issue is that, anytime you have RF flowing in an unshielded wire, it is going to radiate to some extent.
If you don't want it to radiate, then the common solution is to use two wires running in opposite directions
(like the radials on a ground plane antenna) so the radiation from one wire cancels that from the other.
Well, mostly.  When the radials of a ground plane antenna slope downwards,  the horizontally polarized
radiation from the wires tends to cancel at far distances, but the vertically polarized component is in phase
in all wires and contributes to the radiation.

Making the counterpoise 10% short doesn't reduce the radiation - it simply add some reactance so the
counterpoise doesn't work as well.  The outside of your coax is going to work as a counterpoise also.

The truth is, the MFJ-1899 is a gimmick antenna (at least for the 80m coverage).  It's for those who want
to say that they've worked pedestrian mobile, even if they just talked to their friend a block away (or across
a hamfest.)  It really isn't going to work well without some sort of ground system, and that's rather
impractical for pedestrian mobile use unless you want to drag a 60' wire behind you.  And even at that, like
many other small antennas, the counterpoise wire likely will radiate more RF than the "antenna" itself.

I had reasonably good results over a 60 mile path using my mobile antenna out a window for several reasons:
First, it had an excellent ground plane comprised of all the window frames in the building bonded together.
Second, it was full length for a mobile antenna (8') with center loading, using fairly heavy wire to reduce the
coil losses (though it would have been better if I could have made it longer).  Third, it was horizontally polarized,
permitting NVIS propagation over the 100 mile path I wanted to cover.

If you drop a quarter wave wire down the outside of the building, you still have a couple of issues.  The building
may absorb much of the signal, depending on the building materials used.  And you still need a counterpoise or
ground system to feed it against.  A quarter wave wire has a low feedpoint impedance, which can give a good
match to 50 ohms but requires someplace for the other side of the current to flow, otherwise it is like trying
to use a light bulb with only one terminal connected to the power source.

If you use a half wave wire then it has a high feedpoint impedance, and the ground requirements aren't as
difficult.  But you have to match the high impedance.  Also note than in either case your antenna will be primarily
vertically polarized:  typically that would be better for DX but not as good for local contacts.  And you may pick
up a lot of noise from the apartments below you.

Also, while you could use a commercial multi-band end-fed wire, the radiation patterns may not be very useful
on the higher bands.  That's because, as the frequency gets higher (the wire contains more wavelengths) the
maximum radiation tends towards the ends of the wire, and radiating at high angles won't reflect back to Earth
above 40 or so.


But a light wire hanging down the side of the building, on a reel so you can retrieve it easily, and a tuner to match
it, may be about the best antenna you can set up in the circumstances.
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W3NCL
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Posts: 13




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« Reply #7 on: November 27, 2017, 08:28:15 AM »

@WB6BYU - I really appreciate the input! I don't want to call out any hams on other forums, but yes, multiple sources talk about cutting a counterpoise around 10% shorter than a quarter wavelength. Oh well. Regardless, my dalliance with the 1899T may have been short-lived then. I really may drop the EFT-10/20/40 down the balcony via a wheel at the end of a 2-foot piece of PVC to remove the chafing threat to the wire. That should also achieve some stand-off from the building and eliminate the need for a counterpoise. Won't give me 80 meters, but maybe until I change QTHs that's simply the way it has to be.

In the meantime, I'll play around with my 40m mini-dipole (MFJ-2240). Worst thing that can happen is I sell it all at SantaFest on 09 December.

Cheers!

Nico
W3NCL
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WB6BYU
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« Reply #8 on: November 27, 2017, 01:30:55 PM »

In a situation like that where everything depends so much on the specifics of your building and
your balcony, the best you can do is to try different things and see what works best for you.
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W3NCL
Member

Posts: 13




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« Reply #9 on: November 27, 2017, 03:25:01 PM »

Yep, I've resigned myself to doing just that. This afternoon I tuned up my MFJ-2240 40m mini-dipole. I got the SWR down to 2.5:1 and then used my MFJ-9201 tuner to do the rest. At 7.235 MHz it showed 1:1 with the inductance set to E and the Antenna and Transmitter knobs to 0 (full capacitance as it's apparently supposed to be).

At 20W I got no QSOs, but at the end of the day I'm not surprised as various AM stations came online and any ham nets decided to call it a day when even with hundreds of watts they couldn't really communicate.

I just wish I had a good 80m solution...

Thanks again.

Nico
W3NCL
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WW7KE
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Posts: 605




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« Reply #10 on: November 27, 2017, 03:35:48 PM »

Yep, I've resigned myself to doing just that. This afternoon I tuned up my MFJ-2240 40m mini-dipole. I got the SWR down to 2.5:1 and then used my MFJ-9201 tuner to do the rest. At 7.235 MHz it showed 1:1 with the inductance set to E and the Antenna and Transmitter knobs to 0 (full capacitance as it's apparently supposed to be).

At 20W I got no QSOs, but at the end of the day I'm not surprised as various AM stations came online and any ham nets decided to call it a day when even with hundreds of watts they couldn't really communicate.

I just wish I had a good 80m solution...

Thanks again.

Nico
W3NCL

Have you thought about using the Reverse Beacon Network, one or more internet ham receivers, or WSPR on WSJT-X?  At least you'd have some idea whether or not you're getting out, without making a real QSO.  I've found WSPR to be a godsend when it seems like my antenna's not working right.

Reverse Beacon Network:  http://www.reversebeacon.net/
Web-enabled SDR receivers:  http://websdr.org/
WSJT-X:  http://physics.princeton.edu/pulsar/K1JT/wsjtx.html
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He speaks fluent PSK31...  One QSO with him earns you 5BDXCC...  His Wouff Hong has two Wouffs... Hiram Percy Maxim called HIM "The Old Man..."  He is... The Most Interesting Ham In The World!
W3NCL
Member

Posts: 13




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« Reply #11 on: November 27, 2017, 03:43:20 PM »

@WW7KE - I have indeed. It's high on my priority list, but I need to make/buy the right set of cables to connect my X-108G to my laptop. I have the USB cable for rig control and the audio rig-out to laptop-in cable. It's the laptop-out to rig-6-pin-DIN-in that's non-standard. But I'll work it.

In the meantime I'm going to play with the counterpoises for the 1899T vertical. Who knows....maybe it'll work.

Cheers!

Nico
W3NCL
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N7RVD
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« Reply #12 on: November 28, 2017, 07:06:38 AM »

Nico,

Working the low bands, 40 and 80 meters, usually requires higher power and full size antennas.  I have a ground mounted, trapped, "L" for 40 and 80.  Running 500 watts, I have mornings ands evening where I can't seem to break out of the back yard.  The short MFJ antennas you are attempting to use are very low Q, dummy loads and will generally perform prroly, if at all.

You never replied to the query about a balcony.  Do you have a balcony?  Or only an open window?

You will have better luck if you unscrew or detach 1/2 of the MFJ dipole and clamp that to the window frame or balcony so it projects outside.  Attach a 33 foot wire (counterpoise) to the feed point and let it hang down the side of the building.  This setup will actually work pretty well on 40 meters. 

If you try this, do your self a favor and don't waste a minute trying to load it up on 80.  It simply won't work.

Quite frankly, you would be far better off on 15 or 20 meters where shortened, compromise antennas actually will work.

N7RVD
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W3NCL
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« Reply #13 on: November 28, 2017, 07:51:17 AM »

@N7RVD - Sorry about that. I did talk about my 24' balcony in my original post, but I do appreciate your point about using just one ham stick as a vertical with a counterpoise hanging off the balcony. In fact, I'm going to try something similar with my MFJ-1899T, which is a multi-band telescopic whip with a wander lead (supposedly down to 80m). I wasn't planning on clamping it to the balcony, which is probably made of some heavy steel railing clad in thick plastic for appearance. Instead, I have a xmas tree stand with a 2' PVC pipe into which I've stuck the antenna. I was planning to sit that in one of the outside corners of the balcony and the dropping the counterpoise over the side. (Black wire...after sunset...hopefully without neighbors noticing it hanging next to their balconies.



Thoughts?

Nico
W3NCL
« Last Edit: November 28, 2017, 08:12:49 AM by W3NCL » Logged
KK4OBI
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« Reply #14 on: November 28, 2017, 01:15:49 PM »

Looking at the picture, you got me thinking about what I would do in that situation.

The first thing would be to mount the whip on the railing and extend it away from the building.  This the classic "Up and Outer" approach.  Depending on which wander lead connection to the whip, there is always some length of wire hanging from the ground connection that will make the whole thing resonate on a frequency of interest. 

My thought is to use my fly rod reel with some fine magnet wire and a weight. This would be hard to see even if you knew what to look for.  I would try to hang it as far away from the building as practical and not directly in front of any balcony below.

The antenna BNC connector is designed specifically to attach directly to a QRP transceiver or antenna analyzer.  With an analyzer it would be simple to find the the length of hanging wire for each band.  This needs to be done because the radio will shut down if the antenna mismatch gets too great.  I would watch the built-in SWR indicator on transmit.

Because the radio does not have a BNC connector I would use a BNC to SO259 adapter to connect a short coax between the antenna to the Xiegu X-108G.  Band conditions allowing, I am confident I could make contacts from that side of the building.

 
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