K0GKJ – Just Another Ham
The New QTH – A Floating Shack

Final Condo Antenna Tests Successful !

Antenna is now not only up, but leveled and debugged!

Took some effort to get to this point, however. You might find interesting what I found after initial installation…

Guess what… I put the MFJ-269 antenna analyzer on the station (“shack”) end of the feed line from the hexbeam antenna, and was shocked to watch the meter jump wildly in both SWR (standing wave ratio) and impedance (think “resistance”). it is supposed to be of certain values and rock steady. More on this later.

Hmmmm…

I emailed Leo Shoemaker (K4KI0), the supplier of the antenna whose reputation for supporting before and after the sale is stellar, and got an almost immediate response.

As expected he was very helpful with ideas and measurements I could take to zero in on the problem.

Thanks, Leo! Your reputation is well-deserved.

Sounded like a bad connection, Leo suggested, either in my solder joints installing connectors on the roof end of the feedline, or something in the center post of the antenna, very probably NOT anything to do with the wire elements or non-conductive spacers.

Back to the roof.

I first eliminated my feed line as the issue, with the antenna in place.

It did look like the center post of the antenna may indeed be the culprit after getting a few unexpected measurements with my trusty VOM (volt-ohm meter). Resistance (indicator of impedance) jumped around.

Yup, that would cause flakey and erratic SWRs, and weird impedances too!

After removing a couple of pinning bolts and lowering the antenna by manually lifting it and the upper four foot mast section off the top of the lower mast section, hossing it down just five feet (not heavy, just awkward) and temporarily securing it in parallel to the lower mast section (which is bolted to the mansard wall) with strong twine ,while I removed the center post (ugh! a pain, but doable in about five minutes once the antenna is lowered), I took the post down to my test bench.

Yup, the problem was somewhere in that center post. Found erratic continuity between the back of the SO-239 connector (where the feed line connects to the antenna) and the front!

Again, hmmmm…

The culprit: There’s a tiny screw that connects the post’s internal cable harness ground (coax harness shield) to this feedline connector’s outer conductor. That one tiny little screw wasn’t loose, but wasn’t tight either, causing an intermittent connection where a very solid connection is required!

Lesson? Check to ensure ALL connections are good ‘n tight, including the small but important ones like this one!

What’s wrong with this picture? (hex beam, but no center post!):

Checking center post continuity ‘in situ’:

Combined with these nums !! Major league YUCK !! If you don’t get it, read on…

Pulling the center post for further testing and resolution on the bench was not as difficult as I thought since the top of the post, to which all the Kevlar tensioning cords are affixed, comes off the top of the post with some pressure, and can stay connected and in place (whew):

Then it was just a matter of disconnecting each end of the wire elements, the pinning bolt in the baseplate flange, and loosening the two locking allen nuts from the post. Out she came. I did collect all the wire ends that I disconnected from the center post in a cable tie to prevent them from getting unruly in the wind while I was working on the post:

The post went back into the antenna quite painlessly, ALL connections rechecked and resealed (with Coax Seal).

This time I routed the feedline through the hole in the base plate as I should have done in the first place. Functionally, Leo tells me it doesn’t matter, but with the heavy RG-213 coax stuffed through there (and the hole IS large enough to pass the PL-259 connector), it acts as a nice feed line strain relief as the beam rotates.

Note the common mode choke above (for noise suppression), also known as a 1:1 current balun, composed of six Amidon FB-77-1024 ferrite beads available from Ron Mott (W4RDM) at www.hexkit.com at a competitive price. I installed an identical set at the other end of the feed line as well (just in case – as they say, “can’t hurt!”. The rooftop set also has a couple more smaller Mix 77 (best for these HF frequencies) on each end of the six.

Note the generous loop of feedline to allow for 360 beam rotation:

Down in the station, part of the end-to-end “antenna system”, in addition to the antenna, the feedline, two common mode chokes, I’ve also installed a commercial low pass filter to prevent another type of interference called differential mode interference (don’t ask!). Suffice it to say that I’m going to great lengths to PREVENT interference BEFORE it happens. Lots of other common mode chokes on control lines, connecting cables, etc.

 with the bottom of the antenna literally less than a foot above the metal mansard wall (galvanized steel girders and powder-coated aluminum roof sheathing).

I knew the readings would not be good this close to the roof, and I was right, but wanted to see for myself.  Obviously (to other hams), lower SWR numbers (the three right-most columns below) are better, and anything above 2.0 is not good, with 1.0 ideal:

Band Name (wave length in meters)

 

Frequency Measured (Mhz)

 

Antenna down *

 

Antenna up **

 

Measurd in-station

 

20M

 

14.000

 

1.9

 

1.8

 

1.8

 

  14.350

 

1.7

 

1.5

 

1.5

 

17M

 

18.068

 

2.0

 

1.4

 

1.2

 

  18.168

 

2.0

 

1.5

 

1.2

 

15M

 

21.000

 

1.9

 

1.3

 

1.1

 

  21.450

 

3.1

 

1.8

 

1.9

 

10M

 

28.000

 

1.2

 

1.1

 

1.2

 

  29.700

 

5.5

 

3.4

 

2.8

 

Note from these measurements that proximity of the antenna to the metal roof (‘Antenna down’) does indeed impact antenna function – likely an undesirable phenomenon known as capacitative coupling (between roof and antenna) – however, this is a necessary compromise since going higher is simply not an option.

‘Antenna up’ = operating position with the bottom of the antenna just 57 inches above top of metal wall – about the absolute minimum height to get good but not optimal performance. Going higher for better performance is simply not an option here (aesthetically).

Height (AGL) measurements (higher is better):

 

      in feet:

 

Base plate to top of center post:

 

3.58

 

Top of mansard to base plate:

 

4.75

 

Top of mansard wall to flat roof:

 

4.25

 

Roof to 3rd floor deck:

 

  10.33

 

3rd floor deck to 2nd floor deck:

 

10

 

2nd floor deck to parking lot:

 

  11.5

 

       
Height of base plate AGL #

 

  44.41

 

Height of top of antenna AGL

 

  40.83

 

  # AGL = Above Ground Level

 

The good news is that the roof height at over thirty-five feet AGL will be a big advantage over something mounted closer to the ground, metal mansard wall notwithstanding.

Note from the numbers that elevating the bottom of the antenna just a few feet above the metal has dramatically improved SWR (over-simplified, “performance” readings), particularly for the higher frequencies, as I would expect (short distance = greatest influence over higher frequencies that have shorter wavelengths as measured in meters, in case you care!).

Also note that the in-station measurements, including the fifty foot low loss (RG-213) coax feedline, also had some effect on the total “antenna system” as expected, when measuring the entire antenna system end-to-end, with two sets of Mix 77 chokes (noise suppression beads) to suppress common mode interference, as well as a low pass filter to address differential mode interference:

For those of you who care and understand the following, note that undesirable reactance is thankfully very low! No doubt at all (setting aside all humility) because of a well-designed and carefully implemented installation, end-to-end! This is a sweet antenna, and the countless hams that have contributed to its design and refinements are to be complimented!

“The Sweet Spot” within Each of the Four Bands:

 

   
Band Name

 

Resonant Frequency

 

SWR

 

Rs

 

Lowest Xs

 

20M

 

14.205

 

1.3

 

37

 

5

 

 
17M

 

18.090

 

1.2

 

42

 

4

 

 
15M

 

21.095

 

1.1

 

45

 

5

 

 
10M

 

28.229

 

1.1

 

50

 

4

 

 
Rs = “real resistance” component of complex impedance (closer to 50 is better)

 

Xs = “imaginary” component of complex impedance (lower is usually better)

 

Not too bad considering the necessary installation compromises !

Oh yeah, check this out – is life good, or what! I’ve been waiting for four years to see this! I’m declarin’ this antenna now installed, tested and ready to get heated up!

Additionally, the height AGL (above ground level) that the roof provides is an advantage (higher is ALWAYS better), and the minimum elevation above the metallic roof appears to be a reasonable compromise between function and aesthetics from what I can see right now…

I have yet to hit transmit, however, since I’m learning the ins/outs and do’s/don’t’s of my new on-the-air “neighborhoods” by listening first, plus I wanted all filters and chokes installed and tested first (see below).

But even without aiming this antenna (still just pointed north, its home position), the few minutes I’ve spent just listening, I’m hearing stations from Jamaica to Ontario, from Indiana to Alaska, from Iowa to Colorado, mostly on the band I’m most familiar – twenty meter – a longer-range frequency. A

lso listening to more local transmissions from Cape Coral to Naples to Miami, loud and clear.  

This is gonna be good!

By the way, we had sustained twenty plus knot winds for over twenty-four hours, and while the antenna flex’d its muscle a bit, due to its somewhat flexible shock-absorber structure, she stayed right put! Good first test.

I’ll be contacting the local ARES team (Amateur Radio Emergency Service) once I get my two meter (VHF, i.e., very local) band (frequency range) completely operational. I’m already listening to the NOAA weather channels on VHF. Transmitting is next, once I’m sure my HF stuff (all of the above) is squared away. dont want to change too many variables in the equation all at once!  

FB! (fine business, or “awesome”!)

Next order of business – chasin’ a little DX (long distance contacts) to get my feet on the ground, and my ears and voice and brass on the air (‘poundin’ brass’ is what CW (“continuous wave”, or Morse Code) operators do when operating their keys!

I’m reving up for “straight key night” which is one twenty-four hour period each year, starting on New Year’s Eve, where CW operators communicate with each other using only a traditional Morse code key. Big fun after everyone else is done singing “Auld Lang Syne”, kissing everyone in sight, and its then that the real party reptiles spin up the rigs and start the waves hummin’ with dots and dashes (dits ‘n dahs).

I certainly won’t be viewed as a “legendary fist” (a really good CW operator) by then or anytime soon, but I’ll have some fun that too few people on the planet will ever enjoy! Neat connection with history too!

73 (warmest regards) , or dah-dah-di-di-dit  di-di-di-dah-dah, baby! (say that outloud to yourself real fast- wonderful rhythmic symmetry, no?)

de (this is) Gene (K0GKJ)

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