[TowerTalk] Questions on Low band receiving antennas in forests and wetlands along ridgelines and ravines.

[kq2m at kq2m.com]

Mike,

Thank you for your reply and for the link.  I will definitely look into 
it!

73

Bob, KQ2M


On 2021-12-05 20:39, Michael Tope wrote:
> Bob,
> 
> Given your unfriendly terrain, you might consider the Waller Flag
> antenna. You could mount one on a short tower with a rotator. From
> what I have read, these antennas are capable of very high RDFs with a
> relatively small footprint. It consists of two terminated flag
> antennas driven 180 degrees out-of-phase. The 180 degree phasing
> enhances the front-to-side rejection of the array thereby raising the
> RDF, which comes at the expense of output level. The very low output
> level resulting from the 180 deg phase shift requires very high
> common-mode rejection in the feed system to preserve the RDF and a
> very low-noise high gain pre-amp to bring the signal levels up to a
> useful level. You can read more here:
> 
> https://www.kkn.net/dayton2011/N4ISWallerFlag.pdf
> 
> Some variation of this antenna has been on my list of things to try at
> my QTH. Hopefully ham radio will still exist when I finally find the
> time 🙁
> 
> 73, Mike W4EF............
> 
> On 12/4/2021 3:09 PM, kq2m at kq2m.com wrote:
>> I want to supplement my transmitting antennas with the most useful 
>> low-noise low-band receiving antennas possible that I can put up in 
>> dense forest and with extremely challenging topography.
>> 
>> My qth and surrounding woods are on a hilltop with extensive and 
>> steeply angled jagged ledge, many ridgelines, ravines and wetlands and 
>> areas of standing water and marsh, varying in height from ~ 750' - 
>> 820' ASL.  Past where I would be able to put receiving antennas, there 
>> are very sharp dropoffs to South and West of several hundred feet.  It 
>> is beautiful but NIGHTMARISH to walk through the woods under the best 
>> of cndx (like today) but it is a true HORROW SHOW when all the thorns 
>> bushes and dense vegetation is growing rapidly and the Deer Ticks and 
>> mosquitos are everywhere.  It's even worse in snow as the ledge and 
>> rock slopes become exponentially more dangerous to access and there is 
>> ledge EVERYWHERE.
>> 
>> Complicating matters are areas of the woods that resemble the moguls 
>> on a ski slope only more spread out.  Some of these moguls can 
>> approach 30' high with the ridgelines even taller than that. While 
>> they somewhat run in the same direction ENE to WSW others run on 
>> steeply sloping hills like a series of "steps".  One ridge runs North 
>> to South on the side of a hill; drops 15' feet then there is a another 
>> ridge then another drop of 15' or so to a ravine and standing water 
>> and muck pond about 20' across.  And there are flatter areas of ledge 
>> that have what appears to be a boulder on it about 5' high and 30' 
>> long right in the middle of a flat spot.  There are a few formations 
>> like this in other areas as well.  The result is that there are very 
>> few areas open for more than 100' in any direction without running 
>> into these rock formations and steep hills and dropoffs.
>> 
>> Now that I have described the terrain, my questions will make more 
>> sense:
>> 
>> 1) Is that a formula specific to beverage antennas for determining 
>> length?  Or should I used the standard dipole formula 1/2 wavelength = 
>> 468/ f?
>> 
>> 2) What is the effect on a terminated directional beverage (terminated 
>> at the back end that runs downhill at an 8% slope?  If the maximum of 
>> the lobe is at say 15 degrees on flat ground, does the lobe maximum 
>> drop to an even lower angle?  Or does the lobe change? or both?
>> 
>> 3) Same question but with the beverage now running uphill at a 5% 
>> slope.
>> 
>> 4) Same question but with a 20' high "Hump" in the middle? as the 
>> beverage starts and is terminated on a flat spot, runs to the top of a 
>> ridge and then back down again on the other side.
>> 
>> 5) If you put a phased array of verticals NW to SE (with pattern 
>> broadside to the direction of the elements - receiving NE) in a flat 
>> spot that then points directly into a 30' high ridge to the Northeast 
>> 50' from the front of the array, have you essentially turned a low 
>> angle receiving array into a created a high angle receiving array?
>> 
>> 6) What happens when you have 4 ground mounted receive verticals with 
>> that large 5' boulder taking up of the space in the middle of them?  
>> What does that do to the pattern?
>> 
>> 7) Let's say that you have a 6 L array of receive verticals in 2 rows 
>> of three with each line  pointing NW to SE (pattern broadside NE) and 
>> they are phased.  But instead of being on flat ground However, they 
>> are on the side of a steeply sloping hill so that the first row is at 
>> 820' asl and the 2nd row is in the same direction but at 800' asl.  
>> How might that affect the pattern? (for purposes of this question 
>> ignore the impact of ground being "ledge" rather than soil.
>> 
>> 8) Now lets say that you have transmitting antennas for 160, 80 and 40 
>> nearby.  How far do the receive verticals and beverages have to 
>> physically be from the radials of the 160 Inv L, 80 M 4-square and 
>> from the 40 meter wire beam before the performance of either the 
>> transmitting antennas or receiving antennas starts to degrade?  A 
>> formula for distance in wavelengths would be most helpful.
>> 
>> 9) How far apart fractions of a wavelength do the beverages have to be 
>> from each other before their performance starts to degrade?
>> 
>> 10) What is the impact on beverage receive performance if the RG6 Quad 
>> Shield coax to the shack instead of running along the forest floor, 
>> instead runs horizontal and parallel to the beverage?  I am thinking 
>> of keeping it elevated to greatly reduce the opportunity of critters 
>> to chew on it but I don't want to impact the performance of the 
>> beverage.
>> 
>> 11) Is there any performance advantage if I were to terminate the 
>> beverage with a ground rod and radials in that standing water on the 
>> hilltop?  Or does it not make a difference?
>> 
>> Finally, I have read about many preferred beverage lengths for 40, 80 
>> and 160 but few if any seem  to be based on an established formula to 
>> calculate their lengths.  What formulas and multiple of wavelengths 
>> would you use and why?
>> 
>> 12) How many wavelengths on 40 is too long and how many is too short?  
>> Same question for 80?  Same question for 160.  I know that these 
>> answers vary by band which is why I am asking.
>> 
>> They are challenging questions that are not really covered in anything 
>> that I have read.  I would appreciate all of your thoughts and 
>> insights!
>> 
>> Tnx & 73
>> 
>> 
>> Bob, KQ2M