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Posts: 8

« on: March 04, 2013, 03:39:43 PM »

I have a good 4btv hustler that I had on a 2 story garage with wooden roof and 8 radials. It worked just fine. I am now needing to convert it to ground mounted, or perhaps elevated 5 feet. 1. How well might this arrangement work in comparison to roof mount? 2. Several hams have mentioned to me and demonstrated to me how well 75 ohm hardline will work for HF. The reason I need to know the answer is that I have a large quantity of 75 ohm quad shielded and flooded for direct burial coax. Super cable, IF 75 ohms would not pose a problem. I use only 100 watts. 3. If your answer is YES to being able to use the 75 ohm cable, what would you suggest as the maximum run underground? Any opinions, advice or shocking replies will be appreciated a bunch!  73, WA3TJO (Congrats to my XYL for studying from scratch and passing her Technician Exam with a 100% !! ) Grin  If you wish to respond via email it is 

Posts: 1169

« Reply #1 on: March 04, 2013, 06:17:36 PM »

The shift from roof to ground mounted will not be too noticeble if you add more radials, I would not bother with the five foot elevation if considering raised radials at that height, don't think it's worth the trouble to tune 4 bands of radials.
As far as the use of 75 ohm it will be a small mismatch due the 4btv being engineered for 50 match but nothing that some fine tuning at the antenna or shack can't alleviate.

Posts: 295

« Reply #2 on: March 04, 2013, 06:40:20 PM »

To WA3TJO.......
I totally agree with N4JTE. Also, I come from the "old school" that if it works then leave it alone. However, IF...If you do indeed have to move the antenna to a ground-mounted configuration try to lay down as many radials under it as you can. Plus, if its going to be mounted on a lawn that you mow then please look into radial ground staples to hold the radials(wires) close to the ground. Once they(the radials) get inter-woven into the grass(usually after a couple of mows) they will become invisible. Just some food for thought.
My best regards and many 72/73.
Don sr. -- WA2TPU --

Posts: 8

« Reply #3 on: March 04, 2013, 08:57:20 PM »

Hi Guys! Thanks so much for your valuable advice. I appreciate it. Can you please follow up with a couple more opinions? 1. Longest reasonably recommended run for the coax? 2. Optimum numbers of ground radials. 3. Minimum gauge of copper to be used as the radials?  I can't remember the name of the instrument, but it costs about $250. as I remember and it will let you tune your antenna without a rig attached. I will try to obtain one of those and tune with it. Thanks again!! 73, Len

Posts: 8

« Reply #4 on: March 04, 2013, 09:01:49 PM »

I would like to ask one more question. I have a few hundred feet of stranded copper #14AWG with the extra weatherproofing layer. It is THHN wire. Would this be good for the radials? At least the copper will not corrode away with the insulation. 73, Len

Posts: 392

« Reply #5 on: March 05, 2013, 12:01:27 AM »

I put down 60 radials under a 6BTV.  It's probably overkill but when I accidentally snag and break one, I have plenty left...   30-32 radials is a good number and 16 is probably the absolute minimum.  I've always thought the more radials the better, but a series of articles in QEX by N6LF seems to indicate there is little performance gained beyond 32 radials.  I made each radial 55' long but others report good results using shorter radials.  If you are short on space, put down what you can make fit.  

Mount the antenna close to the ground.  THHN will work just fine.  Don's suggestion about using staples and letting the grass roots capture the wire is a really good tip. Here in the desert we either have to bury them a half inch or so or live with the radials exposed.

DX Engineering has a good set of instructions and hints on their web site for the Hustler antennas, including details on mounting and tuning.  Look under the technical documentation section.  I used their radial plate and tilt-over mount and am happy with both.  I have no affiliation with them, I just like their stuff.  

An antenna analyzer is a big help for tuning.  The MFJ-259b is pretty popular but there are a lot of others on the market.  You might see if someone local has one you can borrow.


« Last Edit: March 05, 2013, 12:18:19 AM by K0BT » Logged

Posts: 3289

« Reply #6 on: March 05, 2013, 08:31:05 AM »

-Any gauge is fine from about 28AWG or upward, bare, enameled or insulated

-There is no optimum number of radials.  Impedance tends to stabilize from about 8 radials upwards.  My level of effort is around 36 radials, and no more than 64.  Smiley

-Fancy radial plates are just that..fancy and not required.  Attach the radials directly to the mount, or use a scrap piece of aluminum/stainless, or some copper plated plumbers' tape.  One magazine article suggested using a kitchen sink strainer.

-Remember, radials need to attach as close as practicable to the antenna feedpoint/mount.  Don't mount the antenna on a 5ft post and then run wire to the ground.  That would detune the antenna.  Equivalent to adding 5ft on to the tip.

Enjoy.  bill

Posts: 2276

« Reply #7 on: March 05, 2013, 12:03:59 PM »

The 75 Ohm nomenclature is the characteristic impedance of the line and may vary slightly.
You are placing a 25 ohm bump into the system and at best the match will be a 75 ohm antenna maybe depends on your tuning modifications at the vertical traps matching the feed line and antenna but the rig and all the equipment is 50 ohms characteristic impedance.

Some will think on this fact as OK and support their theory.
Some will not and support a more correct  position.

If you have a built into the rig tuner this difference in impedance of 25 ohms assuming that it is non inductive will be irrelevant relative to you rig output and not necessarily the case for the  transmitted ERP field strength and the dB into your receiver.

Why because

Everything in the antenna line beyond your rig tuner will see a mismatch difference of 25 ohms.
Why deal with that when the antenna is designed to be tuned to 50 ohms avoiding mismatch somewhere beyond the tuner totally in the first place.

One can easily use a 100 ft coaxial low loss 50 ohm antenna line and trap multi band vertical  system performance is expected to equal 100% or very closely.

Height matters

Now to address the height question relative to system performance. The short answer is model the twins from the two heights and make a decision based on your operating goals.

The difference in height between two exact hypothetical elevated vertical systems TWINS above earth surface at  5ft vertical system or raised to roof top height say 15ft is hard to predict because there exists a sky wave variable but what is assigned to the equation is pattern development as a function of height above ground in either of the two identical elevated vertical systems  compared is better understood and can be modeled even when some assumptions are made such as ground conductivity in Milli Siemens frequency in wavelength are all included amongst many other variables,
Because sky wave angles vary and the two previously mentioned systems have different patterns where manifested erp power angles are a function of height above ground the answer can be when that the higher antenna has more major lobes of concentrated power about the semi circle as compared to the lower near earth surface identical twin.

The best answer always involves some variables and as a result, more questions. One simply can not casually, compare easily which system is more utilitarian.

Pick a system and optimize it.

One will not know what he doesn't hear unless one has identical twins and rapid A/B switching between the two and that answer is fluid in time as the sky wave varies etc.

Ground wave or perhaps for direct point to point contacts elevated height helps vertical systems relative to ground mounted vertical systems.

There is differences when a properly ground mounted and flat plane radial system is compared to a properly elevated system at 5ft base height where we install the radial as elevated and dc ground isolated tuned radials properly it is comparing apples to oranges.


Posts: 8

« Reply #8 on: March 10, 2013, 05:48:47 PM »

 Grin I want to give 6,533,550 kudos to all that have assisted me in getting to a reasonable solution. I am VERY impressed with the extreme knowledge all you guys have! It is refreshing and gratifying to know that there are Hams like you guys that are genuinely interested in assisting fellow Hams. THANKS SO MUCH!! ( Don't spend all your kudos in one place! )  73 to all. Len.  73
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