Thursday, August 28, 2014

Simple Ham Radio Antennas: Antenna Basics. Post #291

One of the joys of being semi-retired, is the ability to attend a few more face-to-face meetings with your amateur radio friends.  Such was the case today, Thursday, 28 August 2014.

My xyl had a substitute teaching assignment today, while I didn't.  That gave me some time to go shopping, do the laundry, take care of a few commercials for this weekend's Labor Day Drag Races (I'm the tower announcer and report back to several Hilo radio stations with race results), and meet up with a few ham friends who gather daily at the Hilo Jack In The Box Restaurant.

The meetings are quite informal, with most of the discussion centered around antennas, homebrew projects, and various communications issues.  Despite having 37 years of amateur radio experience "under my belt," I always find something new and interesting at these meetings.

One of the things that has always bothered me is the amount of misunderstanding surrounding antennas, both homebrewed and commercial.  It's hard to sift out the claims and get to the basic "truths" of antenna design, building, testing, and use.  When I raised this question, Dean (KH6B) gave me several reprints of antenna articles from the past which helped clarify my thinking.  Both Dean and I have extensive backgrounds in commercial broadcasting--Dean comes from the broadcast engineering realm of radio, while I stumbled in from the programming and news departments. Dean has built and maintained several AM and FM stations and has served as a consulting engineer on numerous radio projects on the U.S. mainland, Hawaii, and throughout the Pacific Rim.  He has a tremendous collection of reference material dealing with antennas, which he freely shares with those of us attending the informal meetings over coffee and breakfast.

Among the antenna articles I received today was an essay entitled: "Antennas--Some Rules of Thumb for Beginners" by James R. Duffy (KK6MC/5).  The original article can be found here:  http://www.norcalqrp.com/features/bgnsant.html, dated 31 January 2004.

James lists 13 basic antenna concepts that will help you build efficient wire antennas that deliver outstanding performance at a minimal cost.

Here is a brief summary of those ideas:

1.  Any antenna is better than no antenna.  Rather than agonizing over an antenna choice, just put one up and operate. After operating with it for a while, you will become aware of your operating habits and the shortcomings of the antenna you have erected.  That will give you some hints as to which direction you should go with another antenna.  Building your own wire antennas is fun, educational, and fairly cheap.

2.  Higher antennas generally out perform lower antennas.

3.  Most people will be happier with a low dipole than a vertical.  Verticals require a bit more attention to work effectively and beginners can become frustrated in dealing with ground issues.

4.  It pretty much doesn't matter what kind of copper wire you use in an antenna.  The familiar formula for cutting a simple half wave dipole, 468/frequency (in MHz), will give you an approximate starting point for measuring out your antenna elements.

5.Whatever antenna you chose, if it is fed with coaxial cable, you should use a choke balun.  This will prevent the feedline from becoming part of the antenna which can cause all sorts of problems.  Various balun designs are discussed in the ARRL Handbook and in the ARRL Antenna Book.

6.  Buy one of these books and study it well. Antennas don't change much, so even an old copy of the Antenna Book will be very useful.

7.  Outdoor antennas perform better than indoor ones.  A thin wire supported an inch or more away from the building will be much better than one inside.  If you can dangle a wire out a second story window, feed it against a counterpoise wire.  The counterpoise is the "missing half" of your dipole.  You can string the counterpoise around your radio room, being careful not to touch the end of the wire during transmissions.

8.  Don't scrimp on feedline.  Good, low-cost feedline doesn't cost much more than the antenna it is feeding.

9.  Most single band antennas can be made into multiband antennas by feeding them with a balanced feeder like window line and using a tuner/balun combination to keep your rig happy.  This applies to loops as well as dipoles.

10.  If you have antenna restrictions, consider a temporary antenna.  The SD-20 Blackwidow Crappie Fishing Pole can be erected with a wire of choice to make a vertical in a matter of a few seconds.  With a few radials or a chain link fence as a ground, this can give a good account of itself.  If somebody complains about it, take it down and next time erect it where they can't see it.  

11.  Consider your operating practices in choosing an antenna.  If you can only operate in the evening, then even a high 10 meter antenna will not provide you with much operating time.  The band will usually be dead after sunset.  On the other hand, a 40 meter dipole will provide you with a number of contacts late into most evenings.  It can also be used on 15 meters for those occasions when you can operate during the day.

12.  Avoid the temptation to "have it all."  Multiband antennas are often attractive to new comers.  So are electrically "small antennas."  They are by necessity compromises, and usually don't work as well as single band antennas.  I suggest erecting a single band dipole and using it for a while.  As you get used to operating or have desires to try out other bands, you can erect another antenna, or feed the one you have with ladder line for muliband use.  You can build and feed a lot of single band dipoles for the price of a R-7000.  That antenna, by the way, is an excellent performer if you have the necessary money for it.

13.  Homemade antennas are often better and far cheaper than commercially built antennas.  Building wire antennas is educational, fun, and cost effective.

I hope someone finds this useful.  See you on the air--Dr. Megacycle KK6MC/5.

Comment:

During my almost four decades of being an amateur radio operator, I've found the above listed advice and hints true in most cases.  Simplicity, good design, and careful craftsmanship will spell success in the antenna game.  The "Rules of Thumb for Beginners" are technically and economically sound.  Simplicity, stealth, and low power will enable you to stay on the air with a minimum of hassle from your community.

Source:

Duffy, James R. (KK6MC/5).  Antennas:  Some Rules of Thumb for Beginners.  (http://www.norcalqrp.com/features/bgnsant.html.

For the latest Amateur Radio news, check out the news feeds in the blog sidebar.  These sources are updated daily.  You can also check out my Amateur Radio News Site --http://kh6jrm.com.

You can follow our blog community with a free email subscription or by tapping into the blog RSS feed.

Until next time,

73 de Russ (KH6JRM).
Site Administrator.



Monday, August 25, 2014

Simple Ham Radio Antennas: A 3 Band Delta Loop. Post #290.

While I was looking for some loop antenna ideas to try out at my new QTH, I came across this article. Great video which contains numerous approaches to designing and building a multiband delta loop antenna. I will try a variation of this antenna for 40-10 meters using 450 ohm ladder line as the feed line. Aloha, Russ Roberts (KH6JRM).

Thursday, August 21, 2014

The Pine Tree HF Stealth Vertical Antenna. Post #289.

Now that Tropical Storm Iselle has left the state of Hawaii, those of us on Hawaii Island can complete the massive task of clearing roads, restoring power, and, in some cases, rebuilding our homes.

Damage to my home was minimal with only fallen trees and "disassembled" wire antennas to be cleared from the property.  Our subdivision in the Orchidland Estates area of the Puna District escaped serious damage with only power interruption and blocked roads presenting major difficulties.

When I surveyed the damage after the passing of the storm (07-08 August 2014), it soon became apparent that most of my "antenna farm" would have to be rebuilt.  The only antennas left intact were the 40/15 meter inverted vee and the NVIS 40 meter loop, which were lowered before the storm.  My 135-foot/41.15 meters doublet lodged in a 45-foot/13.71 meters tall eucalyptus tree was torn to shreds by windblown branches and fallen debris.  I did salvage the 450-ohm ladder line, a few insulators, and about 100-feet/30.48 meters of #14 AWG house wire used for the dipole.

So, I decided to erect an "emergency" antenna until the other antennas could be inspected for damage and later erected on their former supports.

This antenna would have to follow a set of personal rules that have served me well in the past:

The antenna would have to be cheap, using materials obtained locally or stored at my home.  The antenna would have to be "stealthy" and blend in with the environment; and the antenna would have to be multiband, covering, at the minimum, 40-10 meters.

While I was searching for some antenna ideas, I came across an article written by Tony Milluzzi (KD8RTT), who lives in a HOA-controlled community that frowns on amateur radio antennas.  Tony used a backyard tree as his antenna mast and ran a small number of buried radials (16) from the base of the tree.  He ran a length of buried 50-ohm coaxial cable to the basement window of his shack.  With the tree serving as an impromptu mast, Tony had a multiband HF Stealth Vertical that was nearly invisible.  Aha! That's the temporary antenna I needed while I repaired the mess created by Tropical Storm Iselle.

A 60-foot/18.29 meters tall Norfolk Pine Tree about 65-feet/19.81 meters from the garage/shack would do nicely.  The tree was approximately 2-feet/0.609 meters in diameter, with sturdy 3-inch/7.62 cm diameter branches every 2-feet/0.609 meters up the trunk.  I tried a few of the lower branches and they supported my weight of 180 pounds/81.81 kg--sufficient enough to let me climb up the tree and attach the vertical radiator on the trunk of the tree.

After considering the risks of climbing trees in my retirement years, I decided to rely on my trusty slingshot to launch the antenna into the upper limbs of the pine tree.  I just didn't trust my fate to a tree at heights exceeding my body height.  Better safe than sorry.

Next, using the general formula for a vertical antenna (234/f (MHz)=L(feet), I cut a piece of #14 AWG house wire to a length of 33.01-feet/10.06 meters. The wire was cut to the operating frequency of the Hawaii Afternoon Net (7.088 MHz).  I also cut 4 radial wires to the same length.

As with most of my antennas, I built the device on the ground.

Once I had all of the wires cut, I soldered one leg of the surviving 450-ohm ladder line to the vertical element and soldered the remaining leg of the ladder line to the four radials.  All connections were wrapped with several layers of vinyl electrical tape.  I was fortunate to have 75-feet/22.86 meters of ladder line still intact from the storm.

With the completed antenna and radial system on the ground, I attached a ceramic insulator to the tip of the vertical element and then tied a 100-foot/30.48 meters length of nylon cord to the insulator. A lead fishing sinker was attached to the free end of the nylon rope and would serve as a weighted end for shooting the rope into the branches of the tree.

After a few bad shots, I finally shot the rope over a branch approximately 50-feet/15.24 meters above ground.  The remaining length of nylon cord was used to pull the antenna system up the trunk of the tree. The cord was tied off at a nearby tree stump on the lower portion of my property.

The base of the 40 meter vertical was now approximately 17-feet/5.18 meters above ground.

The radial wires were carefully separated and tied off with nylon cord to nearby rocks and tree stumps.

The antenna resembled a ground plane antenna with gently sloping radials.  Because the antenna wire was colored a light green, I could barely see the antenna elements against the tree trunk and the surrounding brush and scrub growth of short trees.

Once the antenna was in position and the radials tied off, I led the remaining length of ladder line to a 4:1 balun (W9INN balun) attached to my garage wall. The ladder line was kept off the ground.  A 3-foot/0.91 meters length of RG-8X coaxial cable went from the balun to the patch panel in the shack/garage window.

A 6-foot/1.82 meters length of RG-8X coax went from the patch panel to the Drake MN-4 antenna transmatch ("tuner").  Short patch cords connected the Ten-Tec Argosy II, low-pass filter, and Heathkit Dummy Load to the Drake MN-4.

INITIAL RESULTS

With the help of the Drake MN-4, I was able to get a 1:1 swr on 40, 30, 20, 15, and 10 meters. Using approximately 20 watts on cw and ssb, I was able to make contacts with fellow hams in my home state of Hawaii, Japan, and the U.S. mainland.  For a quickly assembled antenna, it performed well and on both local and DX stations.  The worst band was 10 meters which was quite noisy throughout the day.  Twenty and 15 meters were fair to good, with 30 and 40 meters doing well after sunset.

This antenna will serve me well until I repair my multiband inverted vee and check out my NVIS delta loop.

Resources:  

Check out the youtube video and posts from Tony Milluzzi (KD8RTT).  Youtube:  https://www.youtube.com/watch?v=Uk8XD7t3P1U.
 http://www.tonymilluzzi.com/2013/10/my-multiband-wire-vertical-antenna.html.

Be sure to check out the amateur radio news feeds along the blog sidebar.  You can also check into my amateur radio news site for more ham radio happenings (http://kh6jrm.com).

You can follow our blog community with a free email subscription or by tapping into the blog RSS feed.

Thanks for joining me today!

Until next time,

Russ Roberts, KH6JRM.



Wednesday, August 20, 2014

Back From the Dead. Tropical Storm Damage Repaired. Antenna Blog Returns. Post #288

July and August 2014 have proven to be exciting and somewhat terrifying months for those of us who call Hawaii Island our home.

Earlier, I announced that this antenna blog would relocate to my amateur radio news site (http://kh6jrm.com) until I worked out some issues with my ISP and the continuing move to my new QTH in the Orchidland Estates area of the Puna District.  I transferred all antenna articles to that site, as well as keeping the original articles here.

Things turned upside down when Tropical Storm Iselle came ashore on 07 and 08 August 2014.  Many homes in the Puna and Ka'u Districts were cut off by fallen trees and loss of utility poles.  One of those houses was mine, but thankfully, the only loss was the temporary cut in electric power (restored after 3 days) and the removal of fallen trees from my access road.  At the time of the storm, I was working as a reporter from the Hawaii County Civil Defense Office for my former employer, Pacific Media Group, the owner of 4 radio stations in Hilo.  I was quite busy and was not able to reach the new QTH or to continue writing this blog.

Now that the recovery effort is making slow, steady progress, I can resume work on my "homebrewed" antennas and this blog.  My amateur radio news blog will continue publication in that area, while my antenna efforts will be directed here.

Thank you for your patience and understanding.

Since I have to replace all of my wire antennas at the new QTH, expect a few projects in this area.  As before, I'll cite sources and provide appropriate videos for each project.  The internet connection is a bit tenuous, so I'll be using my reserve dial-up connection for awhile.  In either case, the antenna blog is back.

Until next time,

Russ Roberts (KH6JRM).
Site Administrator.