Tech Net Notes January 29, 2010

Loop Antennas

nb5b, Dave, (I believe it was) mentioned that he was thinking about putting up a loop antenna and suggested Loop Antennas as a topic several weeks ago. Having been intrigued with the loop antenna concept for some time, I was very interested in pursuing that topic when I had a chance. That chance came with the January 29th, 2010 Tech Net.

I received the following information from: http://www.bloomington.in.us/~wh2t/loop.html

From WH2T - Dr. Ace's Full Wave Loop Antenna Info

"I have personally used a 160 meter band Horizontal Full Wave Loop antenna with very good success. I worked all 50 states and several countries with 100 Watts using the antenna on the 160 meter band. With a good antenna tuner, the antenna will work 6 thru 160 meters. I currently use a 75 meter Full Wave Delta Loop on the 6 thru 75 meter bands with a tuner. I am very pleased with it."

He goes on to mention that on horizontal polarization he gets about 2.1 dB gain.
He claims the loop is:
Much quieter than a dipole or vertical
Has a broader bandwidth
Usually outperforms a dipole antenna

He feeds his with 75 ohm coax but says 50 ohm can be used.

Dimensions: The formula is 1005/Freq in Mhz = Length in feet
160 Meters at 1.9 Mhz = 529 ft.
75 Meters at 3.85 = 261 ft.

Trimming may be necessary to obtain a low VSWR.

The impedance of a Full Wave Loop is theoretically in the vicinity of 100 ohms.

Connect the center conductor of the coax to one end of the wire and the shield to the other end. Be certain to seal the shield end to protect against water. \

Any shape will work - square, octagon, pentagon, triangle (delta loop), or circle. "The larger the area or aperture inside the loop, the better. A circle has the largest area but is impractical. If you use a triangle shape try to make each leg an equal length as this gives the largest inside aperture or area."

"Note 1 - Don't use a Balun on this Antenna! On a horizontally oriented loop you can feed a corner, center of a side or anywhere. It is unimportant."

"Note 2 - If you know you will be using a Loop, Dipole, Zepp, etc. on Multiple Bands and you want the most efficient performance of the antenna system you will always get less feedline loss if you use Open wire 450-600 Ohm window/ladder line."

"If you feed the Full wave loop antenna direct with a single piece of coax you can only adjust add/prune the antenna til the VSWR gets down to about 1.7:1 at resonance, so you will probably want to use a tuner if you want to cover an entire HF band.. And yes the tuner will work fine as long as you are not using a linear amplifier."

In the article he also includes information on how to determine the length of the feedline using a combination of 75 ohm and 50 ohm coax.

With that we began the net.

kd5avk, Harold, on his mobile from Greenwood, Arkansas, asked if a turner was needed with a loop. After looking back at the information from WH2T it was determined that yes, a loop is needed if using the antenna multiband. Otherwise the antenna will work best only for the frequency for which it is cut.

ae5mn, Hank, asked if the loop antenna can be strung aroung gutters, downspouts and etc. Having installed a myster antenna around the eves of my house with good results, I relayed that I had kept the elements of the dipole in the middle of the eve which was at a minimum the recommended 5 1/2 inches away from most metal objects (including gutters, downspouts, cable TV wiring, and AC service wiring.

kc5zqm, Doug, mentioned that he had used 2 Meter loops for fox hunts and tracking balloon beacons with kc5trb, Harry. In those instances he's used them mostly in the vertical orientation. He mentioned that in SSb mode the horizontal orientation would more likely be used.

k5bbm, Brian mentioned that the loop antenna that kc5zqm referred to may be able to be found at arrowantenna.com.

kf5if, Wade, mentioned a 40 meter Delta Loop that he and the late ae5ft, Gene built at a field day that had a 40 ft peak. The broadsides were to the North and South and that is where they made most of their contacts. It was bottom fed, near the center. No turner was used and SWR was below 2:1 across the band. He mentioned that he was a little disappointed in the amount of noise he had on it and that the high noise may have been due to the vertical orientation and it being in the heat of summer. He did not use an analyzer during the construction, but did use an analyzer afterward to confirm it's characteristics.

End of Net

Tech Net Notes December 10, 2009

We had a very short net on this evening. No questions (until the end) and very few comments.

ke5cub, Lee, made the announcement that he has a CD full of Ham Radio manuals that go back to 1928. If anyone needs a manual for an older radio, Lee will run you off a copy for no charge. If you can reimburse Lee for his ink/paper expenses, that's fine, but not required or expected.

If you have a need for a manual for a piece of ham gear, contact Lee, ke5cub, by phone at 245-0788, or by email at ke5cub@cox.net.

kk5edd, Ed, checked in and said he's trying to decide between an auto tuner and a manual tuner. He would like to know what the pros and cons are. Especially he's interested in folks who may have found advantages of one over the other. This will probably be a topic for our next TARC Net, January 29th.

See you on Wednesday, January 13th!

Tech Net Notes November 27, 2009

After enjoying Thanksgiving Day, and it being a holiday weekend for many, we convened the November, last-Friday-of-the-month, Tech Net on TARC's repeater system at 9:00 PM.

kd5und, Travis, checked in with a problem he's been having with a hum in his radio only when he uses an electret mic. When he changes to a dynamic mic, the hum goes away. When he changes radios, but keeps the electret mic plugged in, the hum is there. He's checked his grounding, changed power supplies, checked his mic shield and tried other radios and had narrowed it down to a problem with the electret type microphones only. Since it happens with other electret microphones, it probably not a problem with the microphones. When the hum is there and he places his finger on the radio chassis, the hum goes away. So the question is "What is the microphone picking up, and from where, and how can it be corrected?"

kd5und, Travis, also mentioned that he's got fork lift batteries for his back-up power and is using a UPS charging circuit out of an old APC unit (with bad batteries) to keep them charged up.

wb5mxo, Guy, checked in and mentioned a w3ff BuddiPole he saw mounted on a three wheeled bicycle. This was in response to an earlier e-mail communique.

n5kh, Will, suggested to kd5und, that he try lifting the ground pin to the AC house wiring to see if there was something coming in on the ground.

ke5wph, Andrew, said that he's getting prepared to put in a 45 ft. Rohn 25 tower and has a question, "What is the optimal guy tension for the guy wires. Regarding Travis' problem. Maybe an RF choke on both positive and negative.

kd5und, Travis, suggested to ke5wph that he tighten his guys to 3 - 6 inches of deflection on the guy cable.

n5kh, Will, mentioned an RF choke as well. Also, does putting a battering in parallel with the power supply filter the noise out? Are there cables running parallel to something that might induce a signal into the power cable. kd5und, Travis, mentioned that the problem does go away with a battery, but that he has not put the battery in the power circuit. It sound like it's either in the power supplies of the AC service to the shack.

kd0cdk, Don, suggested that the 2008/9 ARRL Handbook has a lot of information on noise problems and troubleshooting them. Also he suggested taking the house out of the power circuit with power going only to the shack to see if maybe there is something in the house wiring letting something in. If, during isolation, the problem goes away, you know it's something in the house. Also, have you tried installing a capacitor from the mic positive to ground? Also, are your computers on when you have this problem? kd5und, Travis, answered that he's turned the computers
off and the problem persists.

kd5njr, Scott, suggested that you can check the noise on the AC line with an oscilloscope by taking a few turns around the hot and connecting it to the 'scope probe. That ought to induce enough voltage to see what's going on without putting too much current into the 'scope.

n5kh, Will mentioned that Travis may want to keep an eye on the UPS charging system for his fork lift batteries as many of those UPSs are designed for a particular duty cycle, and the fork lift batteries might exceed that level.

kd5und, Travis, replied that he will start doing that and monitor the output voltage. He said he's been using that system for about 6 months with no problems yet and the system triggers it's alarms whenever he changes the load too greatly.

n5kh, Will, said that the idea to use the UPS charging system is a great idea.

End of Net

Continental Code vs. Morse Code

According to w2csl, Bob, what we now know and use as Morse Code was originally called "Continental Code". It was an upgrade from the first Morse Code that was developed in an effort to standardize code with other countries.

The picture shown above was found by David, my most recent AT&T U-verse installation tech. Dave responded to a call for help from me after I moved my computer back into our "office" from a recent remodeling fiasco.

We had AT&T out about two months ago to put in another Internet drop. The tech that responded then added a line to a temporary location in the house. He did not wire it into the system, but told Jim, our tile installer, how to wire it in when we're ready. So when we moved the computer from the office into our den, we just had to splice in the new wires. That tech told us that we could just leave it that way when we moved back to the newly tiled "office". When we did move (eventually) back into the office, we could not get the internet back up.

David showed up and found that the, now unused, temporary wiring still hooked to the system acted like an antenna and allow enough noise into the system that the signals would not sync in. Our 3-in-one package left us without TV, internet, and phones. All David had to do was disconnect the unused pairs and the system popped back up.

David noticed some of the HAM paraphernalia in the office and we talked a little about it. David mentioned that he had found a handwritten table of Morse Code vs. Continental Code inside a 1901 printing of Longfellow's Poems, brittle from age, which he bought at a garage sale.

David scanned the old document and e-mailed it to me. That is it pictured above.

A teeny bit of code history.



ke5omv
Don

Tech Net Notes October 30, 2009

We didn't get very far into the tech net before the repeater went Ka-bloooey. During a transmission the repeater timed out...and that seemed to have done something to disable it's operation.

Thanks to those who tuned in...or at least, tried to.

Sorry, we'll give it another shot:
November 11, 2009 - 146.910 - 7:00 PM
November 27th, 2009 - 147.045, 443.850 & linked system - 9:00 PM

Enjoy the weather!

Don
ke5omv

Tech Net Notes October 14, 2009

On this one we started off again without a topic.

w5ydl, Dan, changed all that with a question: He said that he's planning on putting up a 6 meter dipole and working 50.125. He asked "Is there anyone who can tell me a little bit about working 6M?

(NOTE: See kd5njr, Scott's comments on this by scrolling to the bottom of this post and clicking on "comments".)

kb5vdb, Ron, checked in and reminded us of Paul's upcoming deployment to Afganistan. In addition Ron passed on the recent new of a husband, wife, and son who died while installing a ham radio antenna. It fell into a 13,000 volt transmission line. Apparently they were not hams, but putting it up for a friend.

ke5yoo, Mike, mentioned that kd5njr, Scott's loop antenna was at about 50 feet. Orientation was the bigger question, with vertical giving you a possibly lower take-off angle. In addition Mike mentioned that ke5otq, Dennis is going to make some 2M loops.

kk5edd, Ed, said that he has been doing PSK31 on 20 meters lately and has plans on mounting an HF antenna onto his 5th wheel, if he can get a good idea of a good way to do that.

ke5yoo, Mike, mentioned that height-wise, one wavelength off the ground is good, but with 6 meters and greater, the higher you get the antenna, the better.

kd5cny, Tom, suggested to kk5edd, Ed that screwdriver antennas usually work well on motor homes and such. He also said that a long wire, hung from trees works better with a tuner. He mentioned that another option might be a vertical.

kk5edd, Ed asked, "Is the vertical you're speaking of, a multi-band?"

kd5cny, Tom answered, "If you have a tuner, the vertical should be able to take care of working multi-band." He added, regarding antenna height, "It's good to get the load of the antenna over the 1st wavelength." He said that between the 1st and 2nd wavelength, there's not much noticeable difference... abpve the 2nd wavelength, there's a lot of difference. He also mentioned that kd5cuz, Craig, has had a problem working his Garmen GPS with his 10 meter radio. He said that when Craig turns on his 10 Meter radio, the GPS quits working. It wont receive satellite data. Turn the 10M radio off, and the GPS starts working again. The radio does not have to be transmitting, just turned on. No problems when he fires up on 2M or 440mhz.

kb5vdb,Ron says that it sounds like the IF is interfering with the GPS and causing the
signals to the GPS to cancel out.

ae5ln, Paul, said that he (also) has been messing around with PSK31. "Where's a good place to pick up a signal?"

kk5edd, Ed answered, "14.070 on 20 meters".

ae5ln, Paul said that on 20 meters he locks up his computer.

kd5cny, Tom, suggested that Paul check the shields on his coax jumpers.


End of Net

Tech Net Notes September 25, 2009

ae5ft, Gene, suggested that "The 2 Meter Band Plan" be a topic for the Tech Net. So tonight this is what we put forth. The following information was taken from an ARRL Repeater Director with a little info mixed in that I found on the net:

Frequency Spacing
States East of the Mississippi - 20 kHz
States West of the Mississippi (excluding Texas) - 15/30 kHZ

Popular Simplex Frequencies Nationwide
146.49
146.505
146.520 National Calling Frequency
146.535
145.55
146.56 (in Texas)
146.58

Simplex
146.4 - 146.58
147.42 - 147.57

SSB
144.200 Calling Frequency
144.20 - 144.275


ke5cub, Lee, was the first to check in with a question. The question was, "What's the difference between resonance of the antenna and low SWR, and how to they affect each other?

We had a few check-ins but no takers until ad5pe, Jay, offered an explanation to Lee's question. I wish that I could repeat Jay's answer, but I did not have my recorder set up and my note-taking failed me. With that in mind I will try to encapsulate that which I can remember. I will do this with the help of:
http://www.radio-electronics.com/info/antennas/basics/resonance.php
http://qsl.net/g3yrc/antenna basics.htm


To start off with, resonance is a vastly overrated concept. But what is antenna resonance?

An RF antenna is a form of tuned circuit consisting of inductance and capacitance, and as a result it has a resonant frequency. This is the frequency where the capacitive and inductive reactances cancel each other out. At this point the RF antenna appears purely resistive.

The capacitance and inductance of an RF antenna are determined by its physical properties and the environment in which it is located. The larger the antenna or more strictly the antenna elements, the lower the resonant frequency.

The magnetic field that your antenna puts out will produce an electric current on any metal surface that it strikes, however if the metal that the signal strikes has a length relation to itself, the current will be much stronger on the object. If the object that the magnetic wave strikes is 1/2 wave length, 1/4 wavelength, or 1 full wavelength, then the induced current will be much higher than if the signal struck an object that was not some appreciable fraction of the wavelength of the signal. An antenna is "tuned" at for an exact wavelength. For that exact frequency that antenna is resonant. Every antenna has at least one exact resonance point.

Antenna resonance is the frequency, in MHz, where the antenna is in a state of electrical balance, which is determined by the length of the antenna.

SWR (Standing wave reflected) is the phenomenon that exists when power which initially was sent into the antenna is reflected back toward the radio. The SWR is measured in a ratio, for example 1.5:1 (or 1.5 to 1). How much power gets reflected back into the radio is dependent on the impedance of the radio/coax/antenna. If it's matched perfectly, the power reflected will be near zero (or said another way, an exact match, 1:1).

The impedance of the antenna is a function of the frequency being transmitted and the point at which the antenna is resonant.

Though your antenna may be resonant at a particular frequency, It is more important that the SWR not surpass levels that would be harmful to your radio. You can talk fine on an antenna that is not very resonant, but a high SWR can burn up the
"finals" in your radio.

ke5cub, Lee, added that "Resonant means that the antenna vibrates at it's assigned frequency. Keep the SWR below 2.1:1."

ae5jz, Tom, checked in and said that on his "waterfall" on PSK 31, there is a signal line less than 7 cycles wide at various places along the band, without modulation. He asked if anyone had any ideas about what that was.

k5bbm, Brian, asked, "At what frequencies do you transmit PSK31 on 2 meters?

kk5edd, Ed, suggested that it may be (according to his reference material) that 144.144 for vhf and 432.2 for uhf.

I don't recall who it was, but I believe someone suggested that the 7 cycle line on Tom's waterfall may be associated to some of Tom's equipment.

With that there were no more check-ins, and the Net ended.