Oubacker Antenna for Portable Operation

Discussion in 'On the Road' started by KE2D, Oct 8, 2014.

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  1. KE2D

    KE2D Premium Subscriber QRZ Page

    Hello,

    I’m considering doing some portable operation as a rover station for the PA QSO party this weekend. I don’t have the time to install the HF rig in the car and provide proper, mount, power, grounding, antenna, etc. However, I think I have enough to make a portable solution my son (KD2AWE) and I can setup and breakdown quickly.

    I have an older (circa 1995) Outbacker Perth antenna (when they were made by Terralin) but haven’t used it since about ‘96. I have read the installation and operation documents on the current U.S. distributor page which seem to be primarily about using the antenna for mobile operations. They suggest that users mounting the antenna on a balcony or railing use a 20-30 foot long x 3” wide copper strap, ala counterpoise.

    I plan to mount the antenna on a heavy-duty telescopic film/TV light stand known as a C-Stand. This extends up to 13 feet tall. I will weight the bottom of the stand with 3 x 25 lb. sand bags (75 lb. total) which will make it stable.

    Unfortunately I don’t have any time to do R&D or testing so I’ll have to take my best shot and see how it goes. Here are my questions:

    Should I use the single counterpoise approach? From what I understand, the counterpoise is either an “artificial” ground, or acts as the missing alternate leg of an imagined dipole depending on what you read. In non technical terms, it “counterbalances” the antenna. The Outbacker documentation is non-specific about length. Other literature seems pretty certain about tuning this to be resonant for the chosen band. I’d like to operate on 40/20/15 and optionally 80/75 (good for local contacts).

    Or… Would it be better to treat the antenna as a ground plane and run radials from it? In this case my understanding is that the radials create the ground plane under the antenna. The theoretical best ground plane would be a copper sheet extending for some distance in all directions. Short of that, numerous wires begin to approximate a similar effect. I can probably only manage 4 to 8 radials (best case). I know this is minimal. More than this will make setup and breakdown too cumbersome and time consuming (roving, not camping). Most discussions on ground plane antennas seem to agree that the radials should be tuned to the band (most typically slightly under ¼ wavelength). I can only make so many radials and a custom set for each band probably won't be practical. I have several lengths of 38' long wire recovered from a salvage op set aside.

    Should I allow the antenna mount (where the shield of the coax also will connect), to be connected to my all metal stand? The stand is solid, chrome-plated steel with HD set screws so it will be DC connected top to bottom. Won’t this begin to act as a counterpoise if it’s connected to the coax shield? I will probably setup in parks and parking lots so my assumption was that getting up 10-13 feet would be best to get above nearby objects but maybe keeping it lower would be better? On 40m I won’t be able to raise the antenna anywhere near a significant fraction of the wavelength. However, on 20m, it will start to get close to ¼ wave (16.5’) and on 15m I may be slight over (11’). I do have a method of insulating the antenna mount/feed point from the stand with some 3/8” Lexan used as an offset interface plate.

    Lots of questions. Little time. Any thoughts greatly appreciated.
    Bob – KE2D
    C-Stand.jpg IMG_20141008_095256.jpg
     
  2. K7WFM

    K7WFM Ham Member QRZ Page

    I've never used my Perth on an elevated mount that tall. I have used it on a small tripod that was about 3ft above the ground using three 25ft radials laid on the ground. It worked very well. The coax shield was attached to the metal tripod and it seemed it had no affect on the antennas performance. I used a 3/8" CB metal mount to mount it to the vertical shaft on the tripod.
     
  3. WC5P

    WC5P Platinum Subscriber Platinum Subscriber QRZ Page

    Outbacker makes a collapsible aluminum tripod for their antennas, but I imagine they are hard to find these days.
     
  4. W9GB

    W9GB Ham Member QRZ Page

    The Tripod counterpoise product is referred to as: Outbacker Outpost (I have one).
    http://www.outbackerantennas.com/outpost.html

    The Outbacker Outpost uses the Beehive/Gumdrop 3/8-24 antenna mount (photo of a gray colored version is attached)
    with a supporting aluminum "L" bracket mount for the Gumdrop and connection to aluminum tripod.
    http://www.cqradiosupply.com/servlet/the-2767/ANTENNA-GRAY-BEE-HIVE/Detail

    image.jpg

    This heavy-duty mount is important for taller/longer Outbacker vertical antennas,
    as the wind load stresses on concentrated at this location.
    This is especially important if installed as semi-permanent, rather than as a true portable/temporary antenna whip.

    A TV, camera, or other tripod can be used --
    BUT they will require a bracket for a the 3/8-24 thread mount of the Perth vertical.
    Wayne Eubanks, KG5RE discussed this is Episode 86 of Ham Nation.

    Penninger Radio produces Aluminum tripods, but would require a 3/8"-24 mount bracket
    https://www.penningerradio.com/gallery.asp?id=54&cc=

    Homebrew Outbacker Outpost Tripod Antenna Mount
    by David Tavener, VK4ICE
    http://www.vk4ice.com/pdf/Homebrew_Outpost_Tripod.pdf

    Jim Burns is the Outbacker Antenna distributor for North America.
    http://www.outbackerantennas.com/index.html

    Outbacker North America, Inc.
    214 Second Street
    Manchester, KY 40962
    606-598-2029
    jfburns@windstream.net
     
    Last edited: Oct 10, 2014
  5. W9GB

    W9GB Ham Member QRZ Page

    Since you mentioned that you will be using this as a "rover / portable station" during the Penn QSO party,
    I must mention that COMMON MODE RF issues are VERY COMMON in this tupe of setup.

    Usage of a GOOD UN-UN / BAL-UN is mandatory to minimize RF issues.
     
  6. KE2D

    KE2D Premium Subscriber QRZ Page

    Thanks for all the advice and feedback.

    I've seen pictures of the Outbacker mounted on the Outpost tripod. I don't have the time or cash to invest in one right now. Trying not to go too nuts. My main motivation is to get out and do some operating with my 15 year old son and maybe decrease his time sitting in front of the computer during the weekend by a few hours. :)

    I don't have the gum drop mount but I do have a stainless L-bracket with insulated SO-239 to 3/8-24 adapter. It is essentially a stainless version of the unit that Warren (K7WFM) posted a link to in the first reply here. I used to have an aluminum one but can't seem to locate it. Years ago, I used this antenna clamped to the stern rail of a 42' sail boat and it worked like a champ from the Caribbean. I was helping my uncle move his boat and was away from home for about a week. A friend was helping me with phone patches back home to my wife who was pregnant with our now 18 year old daughter. I had the benefit of the salt water amplifier then.

    I've been trying to get in touch with Jim Burns all week but I always get the machine despite calling at various times during the day. I left a message with my number but haven't gotten a return call.

    Greg, thanks for the note on the common mode RF. Given that I only have one day left to prepare, I won't be able to get a balun or un-un. However, maybe I'll wind a common mode choke on 4" PVC with some coax tomorrow night if I have time. Aside from winding up with stray RF in the laptop computer and the transmit audio, it also occurs to me that I could wind up with unwanted RF current on the metal stand which may be one good reason to isolate it from the coax shield.

    Tonight I trimmed my 8 radials down to 33'-6" (approx. 40m 1/4 wave). I decided that 38' wasn't resonant on any ham band, they may work well on 40 and possibly 15m but not sure about 20m. They are all insulated. While I don't plan to grab the stand or radials while we transmit, since I'm going to be in public places, I want to minimize the risk to unsuspecting tourists who might get too close before we notice.

    So what is the consensus, should I go with a single counterpoise or ground plane and 8 radials?

    Thanks again to everyone for the input.

    Bob - KE2D
     
  7. KE2D

    KE2D Premium Subscriber QRZ Page

    Post Script:

    The contest is over. We operated as rover from 3 counties. This is our first time trying out the rover mode and we learned a lot.

    On Saturday, we setup in a park in Bucks county, only about 20 minutes from our home in NJ. It was a soggy day, raining most of the morning and staying gray into the evening. We setup the antenna as high as we could on the C-stand and set out the radials. Connecting and setting out the radials takes almost as much time as everything else combined. We had dumb bell weights attached to the end of each radial to keep them from sagging and falling to the ground. We got a late start but once we setup we had no problem making QSOs on 20m and 40m. We worked several DX stations on 20m and got good signal reports both from Europe and various points in the U.S. Everything seemed to be working as good as could be expected. Naturally, the Outbacker has a fairly small SWR bandwidth. We did not have the time to raise and lower it to tweak the "stinger" whip length to tune it better, so we let the internal tuner in our TS-440S deal with it which it did quite easily. It didn't improve radiation efficiency but as long as we were logging contacts, we forged ahead. If we could hear 'em, we could work 'em.

    One thing we were thankful for was no stray RF problems or common mode problems. On Friday night, I hastily improvised a common mode choke (aka "ugly balun") with what I had available: 10' of RG-213 and a short section of schedule 40 x 2 inch PVC. Similar to this:

    http://www.hamuniverse.com/G4APLBALUN2A.JPG

    I don't know for sure if this alone kept the RF demons at bay but it seemed like chicken soup: couldn't hurt. What I've read about common mode chokes mostly recommends about twice this amount of coax but I had to make due with what I had. I attached it directly below the antenna mounting bracket / feed point.

    The park closed at dark so we packed up and went home for dinner. Later, we drove down to the outskirts of Philadelphia and setup in an empty area of a very large shopping mall. Trying to keep a low profile, leery of the anyone driving over our radials, hoping to avoid being chased away by mall security, and a desire to make breakdown as quick as possible, we did not set up the radials. The auto tuner could load the antenna on 40m OK but when we tried 80m, not so much. We operated about 90 minutes and only made 12 contacts. Not very encouraging.

    On Sunday, we drove to Northampton County. Initially we setup with the full radial setup in a park along the Delaware River. The stand was on a slight hill and we pressed two of the legs into the soft, moist soil to try to level it. We had difficulty attaining a low SWR. We operated for over an hour and only made about 5 contacts. It seems that having the metal stand lodged in the soil was an ill fated plan and I believe this is what kept the SWR so high. I also feel strongly that being down at the bottom of the river gorge was killing us too. We folded up and drove to a municipal parking lot atop a hill in Easton. We had a limited amount of time we could stay so we setup without radials. We spent another 30 to 40 minutes and made 5 more contacts but it was a struggle. Some stations could hear us but not complete the QSO. We had this happen at least 3 times which is something I am not used to. My son had a prior late afternoon commitment so we packed up and headed back home.

    I dropped him off and with only an hour left I headed straight back over to nearby PA. This time I setup in an interstate rest area atop a hill just over the river in PA only 5 minutes from my home. Time was growing short but I took the time to put out the radials. I was up and running quickly and with only 35 minutes left in the contest, I made 46 QSOs. At times I had a small pileup going and was working them as fast as I could.

    My conclusions:

    Radials = Good. No trouble working U.S stations and Europe reliably with solid signal reports when we asked for them.
    No radials = Bad, marginal at best. Struggled with most of the QSOs we completed without radials.
    Don't sink your metal stand connected to the coax braid into wet ground.
    Elevation matters. Even on HF. Being down at the bottom of a river valley is a bad plan.
    Under the right conditions (e.g.with radials and not in a trench) the Outbacker can be a very effective antenna. It actually amazes me that the such a small antenna can work so well.

    These are seat-of-the pants empirical observations. I wish I could give some more quantitative evidence but we were trying to keep moving and didn't have time to experiment much and take a lot of readings.

    Beyond the antenna experience, like all other such endeavors (e.g. Field Day), it's the little things that get you. Keeping the laptop running N1MM charged was perhaps our most limiting factor. We powered our radio from pairs of 18ah sealed lead-acid batteries (UPS style batteries). We had 3 pairs of them charged and ready but never needed more than one set (I recharged it during dinner and overnight but it never went below 12.5v). I had hoped to run a 150w AC inverter from one of the sets of batteries to run the laptop power supply and charge the laptop (I know, DC-AC-DC, but makng 19v from 12v for a Dell laptop requires a kind of power supply I don't have). The inverter worked for a few minutes but eventually sounded an alarm and went into "protect" mode. I discovered that it would work fine from the ~14v of the car (engine running) with no problem but it did not like the 12.6v of the batteries. Luckily the computer's battery lasted about as long as we could operate at one stretch but if we needed to operate longer, this could be a serious problem.

    All in all, so many things did work that I can't complain and as I said, we learned a lot. Our call sign will be easily noticed at the bottom of the rover category but we had a good time and that's all that really matters in the end.

    Thanks to everyone for the advice. I have some pictures I may come back and post if I have time.

    See you on the air and 73,
    Bob - KE2D
     
    Last edited: Oct 13, 2014
  8. K7WFM

    K7WFM Ham Member QRZ Page

    Glad you had a good time and made the contacts. I'll have to remember to try and insulate the metal tripod from the antenna mount next time I set the Perth up portable.
     
  9. W9GB

    W9GB Ham Member QRZ Page

    Bob -

    In urban settings, one of the best antenna locations can be found on the top of parking garages with "open" top floors.
    These floors usually have the fewest cars, and virtually empty (commuter usage) on many weekends.

    greg, w9gb
     
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