Thursday, July 30, 2015

Building a new antenna at N6QW ~ Part V

A Potential Major Setback ~ the Rohn H950 Mast

We all have heard the caution about the unbelievable low price and you get what you pay for and most likely the physical product does not satisfy the requirement. I believe I am at that point with the H950 mast. I was at first unsure and more confused about how to actually assemble the mast which I found later involves moving a section beyond a point on the next larger section and aligning a notch on the inner pipe with a hole drilled in the larger section.
 
Once aligned you simply place a cotter pin through the assembly so that the inner section notch rests on the cotter pin and then a clamp mechanism is aligned with another hole in the larger section to force against the inner section. The intent here is to have the cotter pin prevent the inner section from slipping down and the clamp's purpose is to make sturdy the two section. Nice theory.
 
I substituted 5/16 steel bolts with nuts for the cotter pin and assembled 4 out the five sections -- the 5th upper most section would be like trying to use wet spaghetti as a car jack tire iron. Just too flimsy! I am OK with just the 4 sections as I think the rotator plus the section of mast above the rotator could easily raise the height to 30 feet. I am OK with that.
 
I tried to "walk up" the just the four sections and immediately saw that there was a lot of play in each of the mechanically coupled sections. This does not bode well because even with adequate guying the rotational forces introduced into the mast could be significant. I really am beginning to question having 30 pounds of weight acting through a 30 foot long moment arm and the implications to the structural integrity especially about the clevis assembly base. Added concerns involve the thought of pushing up some 60 pounds of weight  through a mast assembly that at this juncture does not appear to be robust.
 
So we are left with several options after having discounted the push up approach.
 
  1. Option 1 is to mechanically assemble the four sections, install the beam,  rotator and finally all of the cables plus guy wires while the assembly is lying on the ground. By using a block and tackle mounted on the roof, the assembly could be pulled into place. That solves the push up concern but the flimsy bolted mechanical joints would still be an issue
  2. Option 2 would be like Option 1, but have all of the mechanical joints be welded. That said the flimsy mast itself could suffer a bend, kink or failure during the raising process. (Same applies with Option 1).
  3. Option 3 would be like the original  thought of a push up mast. My back yard has access that could be used by a bucket truck that could raise the mast section by section. This would add a lot of cost to the project. We would still have the flimsy mast issue
  4. Option 4 involves a different mast structure. SpiderBeam has an aluminum mast made for their hex beam and it was written up in QST. It cost 3X the Rohn H950 --guess there is a message there.
Needless to say I am pretty bummed out! Before purchasing the H950 I contacted the distributor about my plan and asked if there were any concerns  -- well you know distributors all they want to do is sell product. I was told my installation would be a fairly typical use of the mast. The ad says you should not use it for a beam --Dah! But the distributor said a 2 element beam would be OK. Like I said the distributors will do anything to sell product. Guess I need to find an alternate distributor.

All this leaves me wondering just what would you do with a Rohn H950? It would probably work OK if you were supporting a 6 Meter dipole made out of #30 wire.
 
Stay Tuned de N6QW

Building a new antenna at N6QW ~ Part IV

Task Sequencing ~ Step by Step Task List

If you haven't guessed by now this blog is more to cause ME to think about how to install the new antenna and in doing so document and share the information. I tend to get a bit wordy, mostly out of fear that I will fail to include all of the detail needed to do the task. Please bear with me and in future posts I will try to be more economical in my word usage.
 

What goes where and what gets done first?

There are so many individual tasks that must be done and in somewhat drifting back to my days in aerospace manufacturing, we often found that items installed at one station had to be removed at a subsequent station to install the items at that downstream station. That was wasteful and caused a lot of rework and did I mention additional cost. There is also another consideration in that my current antenna mast has to be removed to make room for the new mast. Thus I will be "off air" for a period of time and the goal is to make that the shortest period of time possible.
 
This is more of a process that begins by identifying all of the tasks and to then order the tasks so that there is a logic to the install. Consideration must be given to tasks that can only occur in sequence versus tasks that can be done in parallel. It is difficult to raise a mast unless the foundation has been poured and the concrete cured is an example of sequencing. Again this first list is just items to be done and the second list will put those in a proper sequence (or sequencing).
 
  • Precisely set the area and size of the concrete foundation
  • Build a new house bracket assembly
  • Build the pulley assembly to raise the mast to a vertical position (mast is nested at this point)
  • Develop an MTO (Material Take Off ~listing of all tools, supplies and materials needed)
  • Build shop aids needed for the install
  • Calculate the length of the guys wires and guying anchor locations (two on the house and a third to a nearby fence)
  • Review all the clearances and alignment factors (When the mast is vertical and attached to the house bracket the clevis assembly must be in the center of the concrete base.)
  • Remove the existing antenna
  • Install the rotor on the mast. Include drilling a "pinning" bolt hole to lock the rotor to the mast.
  • Look at the wire run from the shack to the antenna/rotor. Evaluate existing junction box that was used for the satellite antenna as a junction box entry into the shack
  • The existing 20 Meter Extended Double Zepp will be reinstalled on the new mast which will be provide coverage on 40 and 80 Meters. Evaluate the attachment mechanism to the mast ~ most likely one of the guy rings.
  • Pour the foundation & allow three days to cure.
  • Perform a "fit check" of the mast to house bracket and foundation.
  • Without the beam or rotor installed raise the mast to assess the difficulty in raising just the mast and then evaluate the "Armstrong method" for raising the mast with the added weight of the beam, rotator and cables.
  • Erect a temporary random wire antenna for listening purpose while off air.
  • Pour the concrete with the mast in place to insure full alignment
  • Dig the foundation which at this point is a cube of about 1.4 feet cubed (120 Pounds of concrete).
I will be adding to this list and then finalize the sequencing/parallel activities. The final result is a critical path schedule (PERT) chart.


Tuesday, July 28, 2015

Building a new antenna at N6QW ~ Part III

More Front End Engineering

In Parts I and II, I covered looking at some of the basics about where I would place the new beam support mast and the all important dimensional clearances needed to raise and operate the beam antenna. In parallel with that activity I had been "noodling" the three very important components of the antenna system which I will describe here.
 
  1. The mast selection was based principally on cost which hopefully I will not rue the selection I made. A roof mounted mast was ruled out in large part because of the implications of boring holes into the roof of my "California Cracker Box" home. A roof installation most likely would involve a structural engineering review and very likely some internal construction to support the mast, beam and rotator. That also has implications for earthquake safety as we are located in an area of active earthquakes. A permit and engineering review by the local building department would be required if this option was selected. Thus a ground mounted mast was an obvious choice. The Rohn H950 Mast must be guyed with the option of an installation with a house bracket plus some guying which is my plan. The H950 once fitted to the concrete base and affixed to the house bracket is raised section by section until it is at its full height of about 34 feet. The mast itself weighs about 34 pounds, the beam about 20 pounds and rotator about 7 pounds. To this one must add in the weight of the coaxial cable pus the rotator cable which I figure is about another 10 pounds. Since the lower section of the mast is affixed to the base and attached to the house bracket its weight van be subtracted since it is not being lifted vertically. Our initial weight calculation was 34 + 20 + 7 + 10 = 71 pounds. Removing the lower section which I estimate to weigh 10 pounds leaves us with 61 pounds to raise to the 34 foot level. But the force required to lift the assembly vertically is progressive. In raising the first section (which is the top) we have the weight of the mast section, the beam, the rotator and some of the cables. So that comes to 27 (beam & rotator) + 6 (mast section) + 4 (cables) = 37 pounds. The next section lift adds the weight of the section plus cables which I estimate is about 8 pounds thus 45 pounds and the same goes for the remaining two sections which now is 53 pounds and 61 pounds respectively. Raising and lowering the mast is not something you want to do daily. I best start with my body building exercises straight away.
  2. The choice of antenna was again a cost factor. Forty five years ago I bought a HyGain TH3 MK3 antenna and I think it was about $200 which has now tripled in price. Thirty five years ago I bought a two element beam (HyGain TH2MK3) and it was less than $200. That antenna has doubled in price. While I was on a walk in my neighbor hood I spotted a new beam installation just around the corner from my home. It was a Mosley Mini32 which is a 2 element light weight beam weighing in at about 9 pounds. Given its small footprint and light weight it does have some compromises on a lower max power level, and the Front to Back ratio. But it certainly looked attractive which cause me to look at other Mosley offerings. My final selection is a custom (non-standard) offering called the MP-32. This beam uses the driven element from the TA-32 which can handle the legal limit and the director form the TA-32 Jr. antenna thus reducing the weight. The gain on 20 Meters is about 3 DB and the F/B ratio is 20 DB. I do have a homebrew legal limit amplifier which is on 20 Meters and thus was interested in having the higher power rating. Why not buy the TA-32? Because it weighs more like 26 pounds. Since it is a custom build I have about a month wait before it will be built and shipped. That is perfect as it will provide me a window to make all of the other installation.
  3. The rotator is the next key element. The wind load is about 5 square feet and so that eliminates some of the less expensive rotators. If you step up to the larger more familiar rotators you are now at around $700 not including the cable. My research led me to the Yaesu G450 which is rated at 10 square feet and called a light duty rotator. I figure that means it is really good for 5 sq. ft. without too many problems. But the eham reviews have not been so kind with specific comments that the rotator is OK but the control box fails. The Yaesu with all of the hardware you really need to make it work (called accessories), costs about $500 with the cable. I figure if worst comes to worst it might be possible to homebrew a replacement control box using an Arduino microcontroller.
To get a better feel of the H950 Rohn Mast and clevis assembly, the next series of photos show those features. The 2X4 is just a shop aid in the drilling of the 5/8"  base bolt holes. The Clevis will be bolted to a section of 1x4 and attached to the concrete forms to keep the bolts aligned during the pouring and curing of the concrete. When the concrete is cured the 1X4 will be removed (as well as the forms) and then the mast will be bolted to the clevis assembly. One the mast is in place and mounted to the house bracket there will be some final shimming to assure a vertical and properly aligned mast.

Rohn 34 Foot Mast with Homebrew Clevis Assembly

The Clevis Assembly

Clevis Assembly

More of the Clevis

Alignment is Critical to the Install

Guy Rings for Upper Sections

Close up of the Clevis

Oblique View of the Clevis



 

Monday, July 27, 2015

Building a new antenna at N6QW ~ Part II

The all important "Engineering" of the project.

I learned a long time ago that the "front end engineering" of a project is the critical success factor whether it is building a new radio or installing an antenna. I have coined a term that I call "noodling" where much time is spent researching the background information and where the alternative analyses are evaluated. When the mast is 1/2 way up in the air, that is not the time to think about will this assembly support the antenna or will it come crashing to the ground. Haste does make waste and you must never forget that sage advice when engaging in a new project.
 
When I installed the current  fiberglass antenna mast I created a plot plan of my house, where I assessed the available real estate and possible site locations of the support mast. Surprise! I found that my options were really limited when considering the length of the Extended Double Zepp, the attachment point to the eaves and choosing the best direction for working DX. That plot plan analysis is shown below and for the most part the same location of the new support mast would serve the beam installation.
 
The critical factors for the beam install is rotational clearance as the element lengths are in the range 28 feet long and that the eave support is readily accessible. The current concrete base for the fiberglass pole is somewhat diminutive and is unsuitable for the beam mast and so a new base must be designed. The third photo in the series explains it all and the new base will be about three times that size.   Since the beam will be rotational the best direction to point the beam is merely a matter of spinning the rotator to that direction. By the way whether I am designing circuit boards or new antennas the old fashion "quad pad" graph paper I find is an invaluable tool to visualize the project and this is where I started. In Part I, I mentioned that my current QTH is a postage stamp sized lot -- the noodling sketch surely affirms that statement.
 

 
 
So far we have "noodled" several pieces of critical information for the beam installation:
 
  1. The current location of the fiberglass mast is suitable for the beam mast as we satisfy the rotational clearance requirement and there is access to the eave so that the lower part of the mast will be anchored to the house structure using a homebrew house bracket similar (but more robust) to the fiberglass bracket.
  2. The concrete base must be larger in size since the clevis assembly will be affixed to the concrete base using 5/8 Inch by 12 inch long galvanized anchor bolts. The new base will be a cube of about 1.5 feet in each direction. The current base is much smaller and contains a stub piece of pipe where the fiberglass bottom section simply slips onto the stub.
There is a chimney quite near the current mast which is shown below and the mast location in relation to this chimney has several implications. The chimney is 17 feet high and thus installing the beam on the mast presents some "clearance" issues which are best thought of now rather than later. The beam boom is about 6 feet long which means the boom to mast bracket is located at about midpoint thus about 3 feet either side of the mast. A critical dimension is the measure of the distance of the boom as it extends past the chimney. A further critical dimension is that the beam MUST be higher than 17 feet for a full rotation. The second photo below shows the current mast and gives a rough feel of these dimensional considerations.
 

 
 
The discussion so far should give weight to the level of analysis involved to effect a successful installation. Stay tuned. Pete N6QW

Sunday, July 26, 2015

Building a new antenna at N6QW ~ Part I

A New Antenna Installation at N6QW

When I moved back to California in Mid-2013, it was with great trepidation and sense of loss of my beloved extended Lazy H antenna. Moving to a postage stamp sized lot with no trees surely was a step back from my former QTH that was a 1/2 acre lot with 150 foot tall pine trees, located about 500 feet from Puget Sound with a clear shot to Europe. But life can be cruel and we should always think of the glass as half full!
 
My  antenna at the new Southern California QTH was a compromise given the time available, my desire to get back on the air and working with what I had. Subsequently I ended up with a 20 Meter Extended Double Zepp that was arranged in an inverted Vee configuration with the apex at 26 feet and the ends at 10 feet. For the center support I purchased a 4 section telescoping fiberglass pole and bracketed the lower section to one of the eaves on the back side of my home.
 
The antenna is fed with a 35 foot section of 450 Ohm line from a 9:1 Balun which then connects to 52 Ohm coax to the shack. I work all bands and use a homebrew 3 KW "T" type tuner. It was like night and day as compared to my Extended Lazy H. But it was certainly better than being completely off of the air and/or some sort of random wire in the attic.
 
Below are a couple of photos of that antenna. I must have properly engineered the install as it has held up very well but now is the time for something better.
 





 
 
 
Using the experience gained with this install I am replacing the 26 foot fiberglass pole with a Rohn H950 push up steel mast that will top out at about 34 feet which gives me 1/2 wavelength on 20 Meters. I will keep the 20M EDZ and that will be at about the same height as today. At the top of the mast will be a Moseley 2 element beam. This beam which is a custom product uses the driven element from the TA-32 and the director from the TA-32 Jr. The idea here is that you can run legal limit into the beam but it weighs less than the TA-32. Turning this monster will be a Yaesu G450 rotator which has been identified as problematic -- but it is what fit in the budget. The known problems involve the control box and not the rotator --so maybe a chance to design an Arduino based rotator control as a retrofit to the Yaesu Controller
 
 
In Part II I will document the engineering of the H950 Mast assembly which I have modified so that it will fit in a ground mounted clevis assembly. This was done  so that it can be easily raised into the vertical position. From there a similar house bracket will keep the bottom section "vertical". Guying will be used for the upper section to keep things safe and sturdy. There will be a poured concrete base to capture the clevis assembly and keep the base of the antenna solidly anchored to the ground. The clevis assembly was made from standard metal parts manufactured by Simpson products and sold by Home Depot.
 
 
Stay tuned for Part II
 

Saturday, July 25, 2015

First Receiver Tests LBS-II

 
The first receiver tests of the LBS-II. 7/2015

This is my newest SSB transceiver dubbed the LBS-II. It is a single band for 40 Meters and has a 5 watt output. The size is 2.5 inches high by 4 inches wide and 7 inches deep. The IF is at 9.0 MHz using an INRAD model 351 four pole filter. The VFO and BFO signals are supplied using a Si5351 driven by an Arduino Pro-Mini. It took about 3 weeks to construct. See full detail on the build at http://www.n6qw.com/LBS2.html