Saturday, March 14, 2009


I was grinding my coffee beans this morning trying to think of something to write for this blog. It is a challenge to come up with something I think will be interesting EVERY DAY, but it is also a challenge to be risen to. As I brewed my espresso I decided to write about what I am planning and how I intend to get there by looking at where I came from.

My other hobby is to collect antenna parts. Not that I really want an antenna part collection, its just that often I sit in an operating room late at night doing some emergency operation. (I pulls 'em out of the jaws of death, but I don't quite brings 'em back to life until they are all fixed, all at 3AM with "sympathy for the devil" blaring on the CD player. Yea I live a bizarre life) After I get the patient stabilized then its a matter of just running the anesthetic. That's like flying a plane. You have to pay attention, but unless there is something happening there isn't much to do. I basically immerse myself into the physiology of the patient, and together (the patient and me) we fly to the end of the operation. If things start tailing out of control, I bring them back by chemically or physiologically adjusting various systems in the patients body to bring everything back into alignment. I am well trained in all aspects of the patients physiology and pathology and all that gets taken into account as I make my decisions. I litterally take the patients systems under my control, but God was smart and he made the systems pretty self correcting, so except when things are circling the drain its not too hard to do. After 24 years and 20,000 patients, you get to the point where you can anticipate and bring things into control even before they get out of control.

I have ADD so I'm an expert at doing 2 things at once. It helps me concentrate to keep shifting my focus in and out of "frame" if you will, so naturally I sit and design antennas to keep form going out of my mind with boredom. Then since I'm arrogant enough to think I will actually build a design, I collect the parts. What the heck is the point of going to a hamfest if you don't collect antenna parts? I mean you can go there and pump the hands of some of the people you know, but that usually just leaves you with the impression "my God you're getting old"!!! Of course then I look in the mirror... I have a copy of EZNEC on my work computer for just such occasions. I am fortunate enough to have a 2nd garage on the back of my property where I store my parts (I also keep the Christmas tree out there. After Christmas I just wheel the whole thing out to the garage and put a big cone shaped tarp over it till next year, my wife likes the second garage!)

Sometimes I actually build antennas from the parts I collect, and this year I am planning a multiband 2 el vertical phased array. I've been planning a 4 square for a long time and I even designed a high performane self supporting 80M vertical for that project, but in truth the way my property is laid out its hard for me to swing a 4 square and do justice to the radial fields needed, and I won't build the array unless I can have a good radial field. No point in busting my butt in the hot Florida sun unless I actually can get the 5.33 dB from the effort. Its not worth loosing 2dB in a crappy radial sytem. Heck I can get 3dB by just doubling my power. I used to consult engineer broadcast arrays before I changed career paths, and the ground return to the coax is key to a happy vertical. For a simple vertical you can just put in what you can put in and have a whole lot of radio fun, so don't let me discourage you in the least about experimenting with verticals. Why some of my best friends are vertical!! BUT for a high performance array you need to be well coupled into the dirt. To design and build antennas, even antennas that are as well characterized as a simple vertical you need some equipment. Here are a few of the pieces I've built over the years.

The first thing you need is a way to look at impedance at the antenna. I started there with a MFJ-259 (not the B but the old one) and it works OK for quick and dirty. Then I built this, the AA-908

It was a fun project. I upgraded my soldering skill and equipment in learning how to solder surface mount. For an old geezer like me magnification is required, and a good temp controlled soldering iron. I had a blast learning how to do that and my payoff was a very nice meter that worked the first time....I was jazzed

Guess what, the 908 is basically an SDR radio that use specialized software and instead of an antenna it uses a bridge which is then connected to the antenna. Here is a snap of a SWR plot (not mine this was taken form the 908 web site) made with the AA-908

This meter uses a DDS and an A/D converter (just like the first conversion of the F5K) The A/D is only 8 bit. There is a program that allows you to couple this meter to a palm pilot (remember them?) and you can get this plot in the palm of your hand at the antenna (including up the tower).

Of course I wanted more, so I built N8LP's LP-100 (this is one way to get 3dB, note the meter reading)

In fact I was so impressed I built 2. Those are now in full time service integrated into my station so I may just build another.

Here is a plot of what the LP-100 can do as a Digital Vector watt meter

In its essence this meter is a transmitting VNA (vector network analyzer) You use a program like Commander from the DX lab suite to drive your transmitter's frequency and assuming the power out is well characterized (like it is in the Flex radio), you get a very accurate plot of your antenna's impedance. With this kind of data working on antennas is easy, and you don't have to worry that the A/D converter is being sabotaged by strong broadcast stations. Yes did I mention that the LP-100 is basically an SDR? The really cool thing about this meter is that the bridge is done at RF not at DC like most meters.

The bridge which is separate from the meter, actually delivers RF to the A/D in the meter, and from the 2 signals (I and Q ....???? hey wait a minute.... that's just the same as R and jX when measuring impedance!!!!)

Here are some of the things you can do with this meter beside plotting transmitted VNA plots

This is a plot using the meter as a field strength meter on a beam antenna. You point the beam at a source like your buddy a mile away and the program will plot the received signal as you rotate the antenna giving you what your antenna pattern looks like at your station. If you had a helicopter you could fly the source higher and get a 3 dimensional plot (Hmmmm maybe I need to learn how to hover one of these gas powered remote control helicopters a few hundred feet in the air..... Just hookup a 1 watt transmitter and dangle a zepp antenna out the bottom.... wait wait.... that's a day dream meant to be dreamed during emergency surgery....) Back to the point

Here is a smith chart

And here is how you characterize a plot of SWR and its split out components of R and jX

When I built the high performance shorty 80M vertical I of course used EZNEC. (These are not those plots, just an example), but I was able to make some plots that looked at the predicted antenna impedance and the real impedance from my LP-100. It was amazing how well they correlated, and it was fun to be able to actually measure this without spending half the day moving the VFO and writing down the data in a spread sheet. That antenna was almost perfectly characterized by EZNEC including the design of the coil. I highly recommend this program. You can even do a lot of design with the demo version

Also I can't say enough about how cleaver I think N8LP is, plus he is one nice guy.

Of course I wanted more so I built this:

This project pushed my skill to the limit but I was rewarded with a device that could do this:

This is a true lab grade instrument, AND its basically just an SDR!!!! So when I talk about the lab grade quality of F5K receiver I just ain't whistling Dixie.

This VNA is the brain child of N2PK I strongly suggest you spend some time on Paul's website. What he has done at least to me is mind blowing. Paul like Larry is amazing in what he has accomplished.

So there you have it. This is all SDR. This is where our future is leading us. IT IS NOT LEADING US to designs that are basically the 5th, 6th and 7th generation of the Omni-V. That horse is long out of the barn.

Speaking of lab grade receivers, after I wrote about my "SDR-1000/wifi wave guide as remote field strength meter" experience, I thought man what a kludge that was! So I decided to see if I could build something a little less kludgy. I got this in the mail 2 days ago from Tony Parks of Softrock radio

(click me)

This is an SDR you can buy for about $58 which includes all the parts plus a band pass filter daughter board. The radio uses many of the GPL software programs out there including VE3NEA's (of CW skimmer fame) Rocky and of course PowerSDR

With the bandpass filters you can get 160-10 or 80-6. The "new" part of this is the filters are auto switching controlled from the SDR program. This rig uses the sound card in the computer as its A/D, but I have noticed the sound cards in my most recent notebook computers have improved dramatically. My main goal for this project is to build a high performance remote wifi field strength meter, so I just need good enough to get me a 1 dBm scale and the panadapter that I can remote to the base of the antenna so I don't need the ultimate in performance. There is always something to do and learn, that is why Ham radio is so much fun!!!

Each of the above provides a look at some specialized aspect of SDR, that is a radio done in software. We think of a radio as something that eventually demodulates to audio. The simplest of these is a crystal radio. But we can do so much more with the information than just listen to it. We can look at it (panadapter). We can decode it and see the intelligence in what we are looking at (CW skimmer). We can filter it so that whatever is contained in that blip on the panadapter becomes intelligible (brick wall filters down to 11hz and various noise reduction schemes). We can make it do different modes of modulation (try integrating digital radio monidale directly into your OMNI V) and we can make exquisite testing equipment so we can build wonderful things such as antennas!!!

As to my antenna? I'm going to build one of these:

(click the pic)

Note this is NOT an SDR

Click the pic to get to Array solutions Here is an article from NCJ that describes the experience. I was looking at the email header from the one of my beta tester emails from N4HY and low and behold W9AD is one of the participants and I didn't even know it!!!. I want my array to be for 160 as well as the other bands so my next project is to build an highly efficient short vertical for 160. I think I can get 80ft without too much trouble, except I would have to put one antenna in the front yard and I haven't quite come to grips with the aesthetic consequence of that. I bought some wire yesterday to start experimenting with how to turn 67 ft of #12 into a coil that is high Q and stable enough and light enough to be 60% up the pipe during wind and not short out. I figure with this set up I can get a 2/3 size 160 with about 50khz bandwidth, 80M full size 1/4 wave, a 40M full size 1/2 wave and a 30M full size half wave, all phased and optimized. I have the phasing boxes and the coax already in tow, and copper wire is now cheap. I was at the home depot and 500ft of #14 solid is 20 bux, so 200 bux gets me probably a 5 ohm ground on 160.... I have the fiberglass poles and the aluminum to get me at least to 80 or maybe even 90 ft. I lack a couple of 2 1/8 pieces from Texas Towers. One word of caution Don't day dream about antennas See where it gets you?

If you look back you see the brain children of some hams. These are done by one or two or a small group of guys. AA-908, LP-100, Softrock, EZNEC, W9AD array, N2PK, VE3NEA, K5SDR and his brainstorm which is now Flex Radio. Next time you think ham radio is dying just read this blog and you will come away with a whole different attitude.

(man I gotta quit drinking that coffee I thought I'd get about 10 lines out of this riff!!)