The Loss List - Your Shrinking RF Energy Misplacement and Loss in Low Band Antenna Systems An Inventory of Loss Issues and Remedies
Addressing many of the issues below could involve relocating wires, or erecting wires. **Always know the electrical code, including local codes for these installations and their location and follow them.** No dB improvement is worth the risks of insurance-cancelling code violations, possible severe property damage, injury, or even loss of life when these rules are not followed.
DISCLAIMER: Any advice given on this web site shall be construed as withdrawn if following it in a specific location or circumstance involves violating electrical or building codes, unsafe practices or the following paragraph. Readers are solely responsible for knowing codes in effect at their locations.
Additionally, do not use any tree for antenna support, which if partly or entirely toppled could fall into or across power lines. Particularly dangerous are primary lines typically with 13 kV and higher voltages.
At K2AV the base of a 100 foot loblolly pine supporting the 160 Inv L was offset 25 feet from the base of a then planned, now installed 13kV primary pole line along our service road at 35 feet above ground. That antenna site was abandoned when the power company's plans were certified and funded, and the inverted L was moved to a site near the house.
In the three decades K2AV has owned the property, there have been three major weather events which dropped trees along US 64 and the service road which actually fell across power lines, or would have fallen across the new primary lines. Hurricane Fran put thirty or forty trees onto Progress Energy primary lines along a five mile stretch of US 64. Later an ice storm deposited one to two inches radial ice and took down more trees in our local area with longer power outages than Hurricane Fran. And a "derecho" wind event in places snapped full-grown healthy tree trunks at the base. The damage that 13kV could do, coming back up into the house via a 13 kV charged tree entangling wire and feedline, ranges from destroyed equipment to fire to death.
This section will permanently remain under construction, with items added or modified as new information becomes available. Some items will have their own linked explanatory/remedy sections. Providing explanations and drawings as needed may take quite some time. Hopefully many are self-explanatory with intuitive solutions.
Particularly on 160 meters, it's easy for one's TX signal to be right at the distant end's noise level. The failure to QSO may have far more to do with that far end signal-to-noise ratio than with a pileup, especially when competing stations are all operating split and spread over 5 kHz. On difficult propagation paths your sum of remedied loss issues can raise your signal out of the noise for the DX. Even just another dB TX strength may have gotten your signal copied.
If you have not already done so, please read
There is a reason why we focus on issues with seemingly small gains.
Upgrade project installers who have gone through the Loss List were often surprised by the number and sum of loss factors embedded in their existing setup. Some approached twenty issues for remediation. Items with fairly small loss are listed below because enough small losses add up. The best procedure will be to avoid these in the first place, or repair any issue listed on this page unless you have a specific reason to tolerate the issue or delay fixing it.
All of the items on this list have been remediation tasks at correspondent stations. There surely are others as we haven't heard of yet.
Although we would like to be able to put down precise loss factors for each item, the characteristics of dirt underfoot and random local conductors will cause the degree of loss to vary substantially. What fixes a half dB or less in one place could remedy two dB's in another. The trick is simply to get them all if you can. We're not trying to prove the list or numbers to skeptics. We're trying to make your TX signal louder.
160m is significantly worse for ground and dielectric loss issues than higher frequency bands because of its longer wavelength. All else equal, a 160m ¼λ radial will induce twice the length of ground of an 80m ¼λ radial resulting in more than twice the power loss (ΣE²/R). A 160m ¼λ radial will induce four times the length of ground with nearly five times the power loss of a 40m ¼λ. This is because exposure to ground induction loss with a simple wire increases with the length of the wire.
A Listing of Loss Issues
Focusing on SWR in planning and remedy instead of reducing loss - This occurs repeatedly in correspondence. We do need a good SWR IN THE SHACK, particularly with transistor finals in transceivers and QRO amplifiers. But we also need a loss-remedied antenna that performs well on our small properties.
Temporarily forget SWR, concentrate on removing loss. Remedying loss almost always changes the antenna feed impedance, R+jX. Almost always, this improvement also requires some readjustment or redo of the feed system. Frequently the feed system itself was lossy and part of the problem.
AFTER specified dimensions and loss remedies are in place, DO use Method A, B, C, D, or T in
to produce a low SWR in the shack. The matching steps in "Taming" apply as well to almost any aerial wire being used above an FCP -- T, Inverted U, Sloper, etc.
DO NOT modify loss-reducing, performance enhancing dimensions to adjust SWR. Performance will suffer, producing complaints that the FCP did not work.
Insufficient or Irregular Radials
- Radials are not long enough, are not equal length, zigzag, are not uniformly spaced around entire 360 degrees, are not dense enough, or any combination of these issues. Improve radials to full size, linear, dense and uniform all around, or convert to an FCP.
Avoid Inverted L Bend Supported by Tower
- Vertical wire of the inverted L and a tower supporting the L's bend are essentially primary and secondary windings of an RF transformer. We need to avoid this configuration or take steps to reduce tower RF current driven into lossy ground from the tower base. Supporting the bend in the L with the tower involves additional antenna design steps to minimize loss, possibly making other L support schemes more attractive. If you must use a tower and a tree to support, consider supporting the bend at the tree.
Tower Supported Inverted L Bend Unavoidable or Deliberately Chosen
- There are two methods that reduce loss by reducing RF current driven into the ground at the base of the tower. These methods show reduced ground loss in NEC 4.2 comparisons, and in anecdotal results:
For towers 60 feet (18m) and shorter, a solution working in the field, the bend in the L is supported three feet from the tower. The vertical wire is pulled directly down to the FCP center, located 13-15 (4-4.5m) feet away from the tower. This results in a slanted vertical wire roughly 15 degrees off vertical. This method is described in
For towers 65 feet (20m) and taller, the bend and the entire length of the vertical wire are supported 3 feet (1m) from the tower. The FCP is at a minimum 10 feet (3m) above ground. The L/FCP is deliberately isolated from coax, tower and ground, except at a "shorting height". There a 3 foot horizontal shorting wire connects the vertical wire and tower. A table specifies the shorting height per tower height. This method is described in
FCP, adjusting dimensions to reduce SWR
- ** Do not change FCP dimensions. ** This defeats the FCP's cancellation trick responsible for much of the loss savings. It may be tempting because it's an easy reach from ground. The FCP's wire folds are designed to maximally reduce the vector sum of all their fields at ground. Changing FCP dimensions immediately increases loss, especially over poor and very poor urban/suburban "ground". This was one of the first "gotcha" lessons we learned about the FCP in its early development. That low wire was so tempting.
Vertical Wire too Close to Tree Trunk
- Vertical, or vertical wire of inverted L or T is too close to tree trunk. Keep separation from the tree trunk never less than 10 feet (3m), 15 to 20 feet (4.5-6m) if at all possible. It is better to not go quite as high with the vertical wire than heavily induce the tree trunk. Do not go through or over the tree canopy with either vertical or horizontal wire.
FCP supported with electric fence insulators on tree trunks, etc
- As support for an FCP, do not use electric fence insulators directly mounted to tree trunks, wooden fence posts, sides of houses, etc. If an FCP is sturdily supported at the ends and center, simple devices made from small diameter PVC pipe, etc, can push the horizontally running FCP wires a foot away from vertically oriented posts, trunks, and then spray-painted with a color to blend with surroundings.
FCP too close to parallel running dielectric or conductive materials
- To the extent possible keep the FCP 5 feet away from parallel running extents of any material. If the FCP must be run above a fence, try to get the FCP at least two or three feet above it, especially above a wooden fence. Do not run an FCP above a wire fence unless you are able to break up the wires into non-resonant sections.
We understand that "appearance" issues at your site may not allow desired vertical clearance. In these restricted cases with unavoidable loss, creating a foot or two horizontal clearance a little below the top of a wooden fence may reclaim some of the clearance benefit.
Trees, Large Structures Inside Bend of Inverted L
- Other than right next to the wire, the highest RF field strengths of an inverted L occur inside the rectangle defined by vertical, horizontal and ground. A particular lossy item such as a tree inside the bend will result in far more loss in watts than the same tree in front of the bend or well out to the sides. There are measured instances of 2-3 dB RBN improvement cutting down trees inside the bend of an L.
Nearby 80m/40m L, Dipole, Vee, OCF, with Unblocked Feedline
- On 160 meters, these antennas can look like 160 vertical parasitic elements, with part of the vertical wire (coax shield) laying on the ground. Very confusing, they can severely detune the 160 antenna, or keep adjustments to the 160 antenna from having their usual effect. Worse, some configurations can put a lot of 160m power back down 80m, 40m feedlines and damage unprotected attached equipment.
These issues are usually two sources. One is using a balun at the antenna feed, with inferior blocking at 160m. This can be solved by use of available baluns with 4k or 5k ohm blocking at 160. Second, long feedlines without common mode blocking. Commercial common mode blocks should be examined for blocking measurements before purchase. Or one can use DIY devices in
K9YC's excellent 2018 choke cookbook on ferrite devices.
Miniaturized or Undersized Tuners or Components
- Though easily understood for back-packing and summit events, smaller cores and wire sizes, etc. contribute loss that you will want to avoid where possible. The specific
devices recommended here are easily home-brewed. Time for component procurement and construction may require planning well ahead of contests.
Using Whatever Toroid and Wire on Hand for the Isolation Transformer
- Some number of FCP adopters have mimicked K2AV and W0UCE's pre-publish attempts at FCP feed devices. Like the original attempts, they too have left behind torched wire/toroid devices until finally "giving in" to the published specification, joining W2FMI and the rest of us with #2 powdered iron and teflon sleeved #14 heavy polyimide.
Defective or Unsoldered Connectors
- PL259 connectors left unsoldered for testing or quick construction and then forgotten. Connections gradually worsen from increasing corrosion between coax conductors and PL259 metal elements. If not an outright short by carbon paths, deteriorated bakelite center material, mold or corrosion debris in space between conducting surfaces can form a lossy shunt resistance. Water inside connector has an open path to wick into shield, see next.
Water Penetration of Coax Woven Shield
- Water wicking into the fine wire of the woven shield begins the corrosion. This ultimately causes excessive loss not necessarily visible in changed SWR at the shack. Removing the jacket over the corroded shield sometimes exposes completely green corrosion. Process can be slow and sneaky. The coax can become excessively lossy without changing from its characteristic impedance (Z0).
Long Run of Too-Small Coax
- The smaller the coax the greater the loss. Small is often cheap, with related deterioration of jacket and water ingress. If you're buying amplifiers, you should also be buying quality coax well-suited to the use.
Cheap "Copperweld" Conductors with Insufficient Copper Depth
- Sometimes found with bargain "RG-6" coax. Used on 160m, skin effect can be using some portion of the steel for conduction. This is inconsequential at satellite frequencies for which the product was designed. Test the coax for Z0 = 75 ohms and standard low loss at 1.8 MHz. Will not get into the discussion whether to use RG-6 for TX. We understand why some will make this choice.
Using Coax to Feed Severe Mismatch with Tuner in the Shack
- Many antenna solutions really require a tuner at the antenna end of feed coax. Coax loss goes way up if the tuner is in the shack and there are high current maxima between shack and antenna. Purposeful QRO high current on mismatched coax should be restricted to ½ inch hardline coax or larger.
Coax Previously Misused to Feed Severe Mismatch at High Power with Tuner in the Shack
- Very high current at current maximum(s) can heat the fine woven shield wire to the point of turning black and melting/partly decomposing dielectric material. Once misused this way, such coax remains lossy even though it may not affect SWR. TDR analysis of coax may show increasing Z every electrical halfwave on the band(s) abuse occurred.
Poorly Targeted Use of Insulated Conductors
- There are situations where some insulation is simply required. Do not insulate any more than required. Use PTFE or PE insulated wire. Use PTFE sleeving on bare wire. To fix the position of sleeving, use a single bare wire wrapped one turn around cleaned antenna wire at the insulation ends, and then soldered in place. Not soldering will create noise and intermod. ** Do not use PVC insulation or PVC insulated electrical house wire for this purpose.**
Poorly Targeted Use of Stranded Conductors
- Only short lengths of new, never-exposed-to-weather fine stranded wire should be used to go around bending points or construct moving drip loops, etc. Stranded wire should be insulated with PTFE or PE ** and the ends sealed against the weather.** Use WireMan #547 (#12 AWG, 259 strands bare copper, black PE jacket) or its equivalent for this purpose. Do not use PVC insulated wire.
FCP, More Spacing Insulators than Needed
- The 66 foot 160m FCP is adequately supported with separators every 11 feet. They can be made from pieces of 1/2 inch PVC pipe. The end and center separators can be two inch PVC pipe also maintaining height above ground, or use support cord between trees, etc.
FCP, Insufficient Height
- Particularly for poorer "earth" underneath, lower FCP support raises feed impedance of the antenna system, broadens SWR and increases system loss. If at all possible, use a minimum height of 8, preferably 10 feet (2.5 to 3 meters)
FCP, Not Constructing from At Least Solid #12 Bare Wire.
- Early, pre-2012 constructed FCP's used various insulated wires, including (now-disapproved) unstripped PVC insulated #14 THHN. Yes, at one point we did use it in an FCP with ladder snaps from 73CNC every 18 inches. Going to bare solid AWG 12 with 7 total separators significantly improved performance.
FCP, Bends at Other than 1/4, 3/4 Overall Length
- The center-most portion of the FCP, e.g. 1/4 point to center to 3/4 point, or -16.5 ft to center to +16.5 ft for a 160m FCP length is the most important for field net cancellation. Best results are found at 180 degree opposition. Fold an FCP to navigate corners in layout with a 90 degree angle at the 1/4 or 3/4 point. To go around an inside corner consider 45 degree angles at the 1/4 and 3/4 points which will increase distance from FCP center to dielectric material. See illustrations and further detailed discussion. Reading the entire article may be useful.
(USA) Using THHN Wire Without Stripping Insulation
- Extreme loss in certain tests. Though there is a slight reduction velocity factor using unstripped THHN for dipoles, etc, this is fairly minor. Particularly for elevated radials, the insulation vastly increases the capacity of the wire to the ground. Also if THHN is close to leaves and branches, capacity to those is increased as well. These increase dielectric and resistive losses. While trimming the wire lengths will tune out the resonance effects of this extra capacitance, the insulation itself is designed and intended for use in conduits, and is not resistant to UV radiation. The change in dielectric qualities over time imparts a slow detune of initial lengths, and with some insulation appears to increase the capacity. If insulation simply must be used in certain situations, it is best to slip the proper size of PTFE** sleeving over bare wire for just the length needed.
** PTFE is often referred to by the brand name Teflon™, the registered trademark for the PTFE product line of E.I. du Pont.