Author Archives: Frederick Vobbe

About Frederick Vobbe

I have won numerous awards in broadcasting, electronic engineering, and civic service, and has been a finalist for the City of Lima Neighborhood Award numerous times, as well as nominated several times for the national Jefferson Award. I’m presently employed as Director of Engineering for Block Communications, Inc., and I’m Vice President and Chief Operator for the a group of television stations in Lima, Ohio. On the amateur radio side I’m the trustee for the KT8APR repeaters on 53.630, 145.370, and 443.625, and the W8AOH repeater on 146.745 operated by the Allen County Office of Homeland Security. These repeaters are analog, IRLP, and DSTAR. I was the long time editor of the DX Audio Service, a non-profit radio magazine on audio cassette devoted to the medium wave DX hobby. The magazine ran from April 1985 till the National Radio Club shut it down in April 2015, I’m a member of B.P.O.E. #54, Eagles #370, and on the Salvation Army board of directors. I’m a past member of the Lima Host Lions Club where I served as President, VP, and on the board of directors. I hold the Melvin Jones Award, one of Lions Club top honors. In my nearly 48 plus year radio career I’ve worked at recording studios, radio, and television stations. One of my other hobbies is collecting “oldies” from the years 1955 to 1990 that charted in the radio industry. I have my own automation system and Part 15 radio station where I can listen to “good” music. I also restore old recordings of radio jingles, airchecks, and production music from tape and records. Another hobby is designing circuits and home-brewing equipment such as audio processors, tube compressors, switcher & control systems, audio distribution amplifiers, and audio mixers. I’m married to Debbie, who is amazingly tolerant of my audio/RF addiction. We have two children wonderful children, Jonathan and Constance, both grown up and have made their parents proud. I’m Originally from Toledo, Ohio, and lived in Lima since 1985. My ham radio call sign, W8HDU, was granted via the vanity callsign program, and was my grandfather’s call. He worked at Western Union during the days and at night he operated on 80 meters from his home in Toledo using a home brew transmitter and receiver, working the CW mode.

Old School Console

Gates Studioette from the Ross Revenge

Today I found a reference to the Gates Studioette console.  Remember them?  This console resided in the pirate ship Ross Revenge, “The Boat That Rocked”.  If you’re not familiar with the history its well worth an hour of reading!   Radio Caroline was an amazing station.

My first experience with the Gates Studioette was a visit to then WAWR-FM in Bowling Green, Ohio.  The station was on 93.5, mono, and in a college town, Bowling Green, Ohio.  The announcer giving me the tour was Bob Ladd who later went on to own a station in Bellevue, Ohio, on 92.1.   I never forget the tour of WAWR.  It was awesome.

The console was typical of that era.  Tubes, step faders, but the interesting part was the construction.  Note how the chassis was made, the number of brakes made in the metal.  Knobs which you can actually handle.  Then there is the switching on the front as well as the escutcheon plates detailing the function.  Those, by the way, are steel and silk screen.

Today you don’t see that craftsmanship.  Recently I had to look for a console for work, and I was dogged by the fact every darn one of them is either a computer, or a production/stage mixer type of console.   OK, they look cool and futuristic, but they can’t be fixed at the component level, (you’re beholding to a manufacturer), or they don’t “feel” right.

Soon I’ll be starting on converting an old tube Yard, (circa 1958), to a modern stereo console.  The restoration will be interesting as the Yard’s old guts go, replaced by my own designed amps, but I want it to look like it did in 1958.  I’m also adding some options which include mix-minus for the Telos, and solid state relays for the On-Air light and remote starts.

The cabinetry will be the hardest part, as well as replacing switches and knobs.  Presently I’m trying to find a source for the Gates knobs uses at that time.   Due to our economy, (or lack thereof for the past several decades), we don’t make things anymore in this country.  So it’s going to be hard to find a company to make them.  I did find someone to make the switch knobs, except he didn’t have the dye they used to make colored caps.  Only black.

VU meters?  Try to find one.  Most are unobtanium due to the complex nature of the meter.  The specifications are rather narrow, and only new old stock is available.  If you buy any of the VU meters from China, they will likely be DC meters 500mA, and even with an AC to DC conversion, the ballistics are not right.

The bottom line is, after the Gates Yard is finished, I might start on a Studioette.  It’s a classic.  But to make it, it’s going to require learning metal braking, silk screening, and other jobs which we simply don’t do here in the United States.

 

 

April 1st is Here

April 1st is here, so I thought I would mention some pranks.

Yes, I like a good joke if it’s not mean or harms someone.

OK, so let’s look at a few from the past.

The Mackinaw Tunnel

I love the north, and hope to retire there if the locals don’t mind.  I’m an amateur radio operator, and during one long conversation with a friend in Alpena, MI, I had the opportunity to spin a tale.

As I was talking to my friend a mobile operator heading north broke into the conversation rather crudely.  He was sort of an excitable type, using CB lingo, with nothing to say good about the traffic and the way people up in the U.P. conduct their affairs.  From no late night carry outs, to lack of gas stations on each corner to fill up his brand new Escalade, nothing pleased him  I was about to ask him why he even ventured north when he didn’t like it.  That is, until he gave me the opening.

“What the hell is wrong with the traffic before the bridge?  They closed the damn bridge.  I’ve got places to go.”  His bitchy tones were getting me in the mood for some fun.

My friend Larry tried to tell him that they close the bridge during high winds, or ice falling from the bridge cables.  Despite this the fellow argued again and again about how primitive the area was, and how in Detroit was MUCH better as they had a bridge AND a tunnel.

Larry, a civil engineer, tried to explain to him what a 5# chunk of ice falling from 150 feet would do to his car, not to mention people inside.  But our dear Rochester Hills friend was having none of it.  He wanted across now, and there was no debate.  That’s when I talked to him.

“Have you thought about taking the private tunnel?”  I asked.   There was silence then he asked about it.  I could hear the reel on the fishing pole spinning.  I hooked me one!

I explained that they had a bad storm and closed the bridge for a few days.  Then after reopening it, a herd of jackalopes blocked all lanes for a few days, and they were on Governor Snyder’s endangered species list so you can’t disturb them until they crossed.  Jackalopes are small so they take up to a day to cross.  Then the timber trucks from the U.P. had to cross so they could make their deadline at the Grayling Toothpick Factory.  Because of situations like this the locals built a private tunnel.

The tunnel to the other side was one lane each way for cars only and the toll was a buck.  The guy was amazed that it cost only a dollar toll, but Larry jumped in and reminded him it was a private tunnel and not on the highway system.  He also said the locals didn’t want anyone to know about it, but it’s on Huron Avenue behind a bait shop.

The fellow thanked me, and I told Larry I would catch him later and turned off the radio not wanting any more questions.  I often wondered if anyone ever clued him in.

The Moose At My Radio

As I mentioned, I’m an amateur radio operator.  While on vacation on the North Manistique Lake I set up my portable amateur radio station, consisting of a Yaesu FT-857D,  tuner, and dipole antenna.  I then started talking to friends back south.

Some amateur operators like to collect grid squares, meaning locations across the United States within specific boundaries.   There is a map on QRZ.COM if you are interested in what they look like.

We’ve all had that person who hangs around, either at a party, or in a conversation.  That friend who says they just need to stop “for a second”, and 5 hours later they are still hanging around.

I was just about to shut down for the morning when I got called by a fellow on the radio who interrupted my conversation with someone else.  Apparently he needed my grid square for his count.  He asked where I was and I mentioned, “I’m at 46° 18′ 4” North by -85° 43′ 59” West, which is grid EN76dh.  I’ve got to sign off.  People are waiting for me.” 

The fellow took this to mean that we needed to strike up a long conversation.   After several exchanges, and reminding him each time that I needed to go, (and the fellow not taking the hint), I figured I needed to create some drama.

On my last communication with him I said.  “Can you hold on a second.  There’s a moose wandering into our campsite.  Wait …. the moose is coming toward me.”  I then made a snorting sound.  “Oh no!  The moose is eating my radio.  Someone needs to get this moose before …….

From this point on I didn’t transmit again, however the fellow I was talking with continued to call and ask questions for the next 20 minutes.  Priceless!

Erasing a Record

When I was a DJ I pulled a lot of pranks and told a lot of jokes on the radio.  One such joke was to explain how records worked.  After giving the explanation I mentioned that records were like audio tape and could be erased, but it only removed the vocals from the record.

Little did the audience know that some 45s pressed at the time had the full song on the A side, and then the B side was the instrumental without vocal.

So I started to play the Barry White song “You’re The First, The Last, My Everything“.  After playing about 15-seconds of the song, I stopped it and explained that I was about to erase the song’s vocal off the 45 RPM record.   I made a sound effect and then played the B side of the song.   It was surprising how many people thought you could erase a record.

Mr. Lyons

At one station I worked at we had a salesman who, honestly, looked like Conway Twitty, but acted like Herb Tarlek.   No, he was worse than Herb because this guy was always jazzed, and many of us suspected he was on uppers.  Good salesman.  Obnoxious creep.

On the morning of April 1st he came in the station to discover his usual mail and pink telephone message slips.  One of those was a slip that said “Call Mr. Lyons at 313-xxx-xxxx.   He wants to place a rather large ad buy for 26 weeks.”  He called and didn’t quite catch on until someone clued him in.  The number was for the cat house at the Detroit Zoo.

After he figured it out he was on the warpath to find out who pranked him.  This only lead to staff members finding pictures of lions, tigers, and bobcats in the newspaper and magazines, and depositing them in his mail, sales files, desk drawer, and anywhere he would discover them at a later date.

The Pettisville Drive In Theater

In the late 70s I worked briefly at a radio station in Archbold, Ohio.   Down the road a bit was a little town called Pettisville, Ohio.  The town at the time was probably only a thousand feet long in any given direction. It has a population of only 498 now, and I would bet it was a 1/3rd less back then.

One April 1st morning I announced that the town now had a drive in theater, and created some commercials to go with gag.  Movies like “American Hot Car Wax”, and “National Lampoon’s Animal Hospital”, and “The Catbox from Outer Space.”   Of course this was outright humor, and the tag line to all the commercials was “The Pettisville Drive In Theater.  You can come as you are, but keep your kids in the car.

Most people took the humor in stride, and thought it was funny.  But apparently some people took it seriously as after my shift I was summoned to the station owner’s office and told to knock it off as it was causing some concern in the small town.  Someone from the little town had called the owner saying that they didn’t appreciate the humor.

These same people had kittens over the Col Sanders Obit.

Toledo Edison Transmission Line Cleaning

At the same station, and as a public service, I reminded people in Delta and Swanton, Ohio, that they needed to place sandwich bags over wall receptacles and light fixtures with no bulb screwed in.   “Toledo Edison will begin cleaning their transmission lines out in the country by using compressed air in the wires.  We all know that birds sit on the wires, the transformers, and poles, and we all know what birds do from time to time.  So if you don’t want bird poo to accidentally get into your hours, cover any receptacles and sockets and you can confine the mess and throw it away.

After saying this on the air I had a lady call me and ask, “How will I know when it’s safe to take the bags off?”

I had to go back on the air and mention that cleaning was starting at 9AM, and would be done by 11AM, so if you didn’t have anything in your bag then it meant the utility probably preemptively vacuumed some of the wires a week earlier.

I also explained that some of the transformers had vac units in them, which was why some had brown stains down the sides.  (In reality it was rust).

At least I didn’t do what WEBN-FM had done for years, and broadcast a fake parade which usually got people out of their homes to find the non-existent parade in Cincinnati.

I miss this sort of thing on the radio.  Today with social media, and news organizations picking up stories without vetting them, a good DJ prank would be a welcomed relief to dull airwaves.

 

The Rescue of the VB28FM

HyGain Model VB28FM

Growing up with depression era parents and grandparents I learned a good lesson.  Don’t be quick to discard something which might have value.  Something broken can be fixed, and with some sweat-equity you can realize something expensive for very little money.

Recently I found a pair of HyGain VB-28FM antennas. The ham who had them was not happy with them.  These antennas had been up on his tower since the mid 1980s, were quite corroded, and in sad shape.  He was tired of 2-meter FM, (working distant repeaters).  He concluded the antennas were no longer of any value to him and he wanted them gone.

I took the antennas because I love to experiment and refurbish antennas. And contrary to his assumption these are “FM only antennas” these will work great for CW and single sideband in the 144.00 to 144.30 MHz range.

INTRODUCTION

The HyGain VB28FM has been around for a while. The VB-28FM is still in production and a manual for the antenna can be found simply by Googling “hygain vb28fm“. I’ve found VB28FM antennas for anywhere between $69.95 to $100 at various web sites.

The VB28FM’s bigger brother is the HyGain VB-214FM. The little brother is the VB-25FM, and little sister is the VB-23FM. The design of each antenna similar, but each model has a different number of elements, and of course, gain.

The VB-28FM’s stated frequency range is 144-148 MHz, which encompasses the whole 2-meter band.  It’s further stated that the antenna is good for 4 MHz bandwidth with a maximum VSWR or 2:1.  I did find the original antenna slightly less bandwidth than claimed.

The gain of a VB-28FM is 14.0 dBi, or 11.8 dBd.  The front to back ratio is 20 dB.  The stated maximum input power is 250 watts continuous, or 500 watts PEP.  Half power beam width is 43° in vertical operation, or 36° in horizontal operation.

HyGain VB28FM Antenna

HyGain VB28FM Antenna

The VB-28FM has 8 elements, and is 148.75″ long. The widest element, (the reflector, tip to tip), is 40.250″.

The antenna weighs 4.25 pounds, and needs about 80″ of turning radius when operating them in horizontal polarization. In reality you should have more space to limit VSWR reflections.

When installing a second VB-28FM in a stacked arrangement it’s recommended that the antennas are placed 1 wavelength apart at you operating frequency, which should also be the best match.

A good formula to use for spacing in inches is ((300/f)x39.3637), where f is your ideal operating transmit frequency.  Keep in mind you’ll have to make a 75-ohm power divider to feed both antennas in phase.  I’ll explain how easy this is later.

FIRST THOUGHTS

Element Attachment

Element Attachment

The overall mechanical design of the antenna is good, but could use some improvement. The elements are held in place with a routing eyebolt.

An element goes into the boom, through the eyebolt, and exits the other side. The eyebolt is then tensioned up to hold the element in place. As you can see from the picture the existing bolts were quite rusted. The instructions call for the eye bolt to be attached using (2) 10-24 nuts torqued together.

I found over-tightening of the nuts can bend the element. Instead of it being straight across the boom at 180-degrees, it may be 177-degrees. Once the element can not slide back and forth inside the boom it’s tight enough.  There is no need to over-tighten.

Feed-point of the antenna

Feed-point of the antenna

The feed-point of the antenna is a “wire lug” connection with the shield of coax going to the boom, and the center conductor feeds one of the driven elements.

The signal is then fed to the second driven element using a 1/2-wave section of RG-58/AU coax.  A “hairpin” attached to each driven element and grounded to the boom of the antenna.

Although the picture is blurry, you can see the connection was very rusty from the hardware, and the coax was basically rotted out due to being exposed to the weather.

RESTORATION

The first thing I did was to disassemble the whole antenna and straighten out the elements which were bent. The elements were scoured with steel wool to remove corrosion.  One of the boom sections had a slight bend at the first director but it was not enough to cause any concern.

Eyebolt

Eyebolt

I replaced all the eyebolts which held elements in place, (along with the zinc nuts and washers).  To make these antennas right, stainless was the only way to go.

I found stainless steel, 10-24 Thread, 1″ Shank, 7/8″ Thread Length Routing Eyebolts at McMaster Carr. They were p/n:9489T54 and cost $7.55 per pack of 5. You will need at least three packages for the VB28FM.

I also replaced the (2) 10-24 zinc nuts with (1) type 316 stainless steel nylon-insert Hex Locknut. These were available from McMaster Carr in packs of 100 for $9.42 and are p/n: 90715A011.

The type 18-8 stainless steel internal-tooth #10 lock washer is available in packs of 100 for $3.63 and are McMaster p/n: 91757A107. I typically buy 100 packs as I know I’ll need more hardware later for other projects.

Feed point of the antenna

Feed point of the antenna

This brings us to the feed point, which I feel is a critical factor in antenna design, but was the most compromised in this antenna’s construction and design.  The hardware was rusted, and the connection depended on bare wire attachments of the transmission line and the phasing cable.   This may be OK on a TV receive antenna, but the RF connection to the antenna should be a standard UHF or Type-N.  The phasing harness would have the same integrity and be protected from the elements.

Box for RF Connections

RF Connection Box

I decided to standardize with a small outdoor rated, sealed aluminum box using a Type-N connector for the RF input, and (2) BNC connectors for the phasing line.

To insulate the antenna connection points from the box, nylon unthreaded spacers, 5/8″ OD, 1/4″ long, and tooled for a #10 screw were used. These are McMaster Carr p/n: 94639A170 and were $8.24 for a pack of 25. The box is a Bud AN1302, Natural NEMA 4.53 x 2.56 x 1.18″. It’s Mouser p/n: 563-AN-1302 and cost $9.40.

RF Input Connector

Amphenol 172117 Type-N

Because the profile of the box is small, (to limit wind load), I had to use an Amphenol 172117 chassis connector. It is Mouser p/n: 523-172117 and costs $5.53.

The connector Is designed to mount to the outside of the box with one penetration hole to feed through the RF, and four connection points.   (4) #4-40 stainless screws with stainless washers and nut hold the connector.

VB28FM(17)The feed is rather simple.  The RF input connects to one element, and then exits to the phasing line.  The phasing line is connected to (2) BNC connectors on the box, Mouser p/n: 523-31-221-RFX and they cost $1.63 each.

The BNC connectors mount through 7/16″ holes in the box, with the connector nutted from the inside.  Be sure it has a lock washer and it’s snugged tight.

For the feed point phasing line I used Andrew FSJ1-50 transmission line. This is HELIAX®, Low Density Foam, corrugated copper, 1/4 in, with a black PE jacket. The loss of this cable is 1.52 dB/p 100′. Each line is 35.23″ (including connector on end).  For two antennas I needed two lines.  I also need (2) connectors to go on each cable. The RF connectors for FSJ1-50 which mate to BNC female connectors are mfgr p/n: F1TBM-C and cost about $23.00 each from RF Parts.

Molex Terminal

Molex Terminal

The physical connection between the #10 screws on the antenna and the RF connectors is by a Molex star ring terminal, 22-18 AWG #10 Stud, p/n: 1907-40033.  found these at the local hardware store.

Soldered to the terminal is a short piece of Belden 83030 Teflon hook-up wire.   This is a stranded 19×29, 16 AWG Silver Plated Copper wire ideal for interconnections.   The MIL spec rating is 1,000 V, 200°C. All wire is inside the box.  When connecting up the lug to the RF connector, use the least amount of wire possible.  Loops, or the wire laying against the box forms an inductor or capacitor at VHF frequencies.

SIDEBAR: In keeping with my motto of Quisquam dignitas effectus est dignitas super effectus, you may want to alter your phase line to limit the cost. You could use RG-58, RG-8 or any 50-ohm cable. You need to make your sections of line 1/2 wavelength with propagation factor, internal wiring, and connector length factored in. I used the FSJ1-50 because of its rigidity and ease in mounting to the antenna.

Your phasing line and antenna feed will be an integral part of your antenna. The lines and RF connectors must be able to handle your maximum power. They will also have to be tough enough to stand up to weather.   Don’t use bargain-brand electricians tape.

Wrap the entire connection twice with 3M Scotch® Super 88 electrical tape. Then wrap the entire connector twice with 3M Scotch® 2242 rubber electrical tape. Then the last wrap the is twice with 3M Scotch® Super 88. Makes sure there are no gaps, and your layers are overlapped by at least 1/8″.

Start at the box, wrapping around the connector and cable till you get about 1′ to 2″ down your transmission line, then go back to finish the second wraps.  Never apply CoaxSeal directly to an RF connector.

Look over your work and make sure there is no way for water to get in. You don’t want to have to take down your antenna to make a repair in the dead of winter, or in the middle of a contest.

ASSEMBLY

Now that the antenna is cleaned up, new hardware is installed, and we have all our parts, let’s shift into the assembly mode.  First, we must make some changes to the antenna’s driven element.  The screws which presently hold the driven element saddle in place are removed.  So are the two screws holding each of the driven elements.  We will replace these with #10-24 2.5″ long stainless steel machine screws.

Driven element saddle with elements and hairpin. Image 2 of 2.

Driven element saddle with elements and hairpin. Image 2 of 2.

Driven element saddle with elements and hairpin. Image 1 of 2.

Driven element saddle with elements and hairpin. Image 1 of 2.

The sequence is to put a lock washer on the screw, then a flat washer, and then attach the hairpin to the elements.   On the bottom of the saddle you have a flat washer, lock washer, and then a #10 nut.  Tighten snug but don’t over tighten and break the saddle.

Next you place another 10-24 x 2.5″ stainless screw through the saddle.

At this point we can attach the feed point.

Before attaching the feed/phasing box, put the following hardware on the threaded ends which will go through the Teflon spacer.  A #10 nut, followed by a lock washer, then flat washer.  The flat washer will end up against the Teflon.  Make sure the nut is down about midway into the mast.

Inside feed box. Input on right, the phasing lines connect to the left connectors.

Inside feed box. Input on right, the phasing lines connect to the left connectors.

Attached the feed/phasing box to the mast by the center screw, and then on the inside of the box place a flat washer, lock washer, and nut.

Tighten so the box is solid against the mast.

Be careful not to allow the box to pivot, bending the screws from the driven elements, or damaging the Teflon.  Everything should be square.

It’s OK that you have the extra length of the screw in the box.  Testing the box with the 2.5″ and a 2.0″ does not show any difference in impedance or performance.

Feed & phasing is mechanically attached by pressure against the Teflon spacers.

Feed & phasing is mechanically attached by pressure against the Teflon spacers.

Place a flat washer over each screw, then place the lugs over the screws as shown.  The right wire is the input to the antenna.  The wire to the right of this is the outgoing feed to the phasing line, and the wire below is the return from the phasing line.

Tighten “finger tight” a #10 nut on top of the lug.  Here is where it gets interesting.

On the outside of the box, start tightening the nut on the screw till the flat washer is against the Teflon.  The tighten the inside.  Go back and forth till you have the Teflon wafer equal length inside and outside of the box.  You can eyeball it.  When done you should have about 1/16th of an inch inside and outside the box.  Double check to make sure the hardware is tight.  Then you can attach the lid onto the feed/phasing box.

Completed feed/phase box.

Completed feed/phase box. Phasing line on left.

The box should look like this, with the feed coning in from the right, and the phasing line on the left.  The loop I made was scientifically calculated.  (humor)

It’s several turns around a can of bee killer spray, with two ty-wraps to hold its shape. and then connected to the box.  After connecting everything, use one wrap of Super-88 tape for a courtesy wrap, the rubber tape, and the complete with Super-88.  Make sure you mold the rubber against the box.  Getting water into the box is not good.

In the image above, you are seeing the box as mounted on the TOP of the antenna.  Water should drip down over the box, so before we move on, put some silicone rubber or tub caulk around the edges of the Teflon on the bottom to keep water from somehow getting in.

Drill out the tapped screw hole.

Drill out the tapped screw hole.

#10-24 x 1.50" to a locknut.

#10-24 x 1.50″ to a locknut.

Now let’s fix the hairpin attachment.  Remove the screw which held the clamp onto the boom.  Drill it out, and drill through to the other side (top) of the mast.

Pass a #10-24 x 1.50″ screw through from the top, and then reattach the clamp with a #10 lock nut.  Tighten generously, but don’t crush the mast.  This mechanical connection will work better than the old self tapping galvanized screw.

The feed point is now complete!  At this point you might want to take some VSWR measurements, or if you’re lucky enough to have a network analyzer you can check to make sure the feed is 50 ohm and the reactance is as close to zero as possible.  If you can get somewhere between 47 and 53 ohm, ± 30j, call it good.   As you’re testing, bang on the boom while watching the VSWR to check for loose hardware.  You don’t want to put an antenna up, only to have to take it down for repair.  Check your connections!

The cable feeding my antenna is part of a phasing harness for running two antennas to increase gain.  Let’s look at how that’s done.

 

PHASING TWO ANTENNAS

Phasing two antennas is not that hard.  You need 75-ohm cable, (4) Type-N connectors, (1) Type N “T” connector, (1) Type N 90-degree connector, a tape measure, calculator, and some patience.

First, place your antennas where they would need to be.  In my case I have two horizontally polarized beams, one over top of each other.

Second, calculate the length of the line.  A phasing line for two antennas is an odd wavelength.  In other words: ¼, ¾, 1¼, 1¾, 2¼, etc.  You also need to know the propagation or velocity factor of the cable.  You can find this in the manufacturer’s specifications.  But for now let’s assume we’re using RG-11A quad shield.  That has a Vf of 0.66.  (Sometimes it’s expressed as a %).

 

FINAL ANALYSIS

I was getting a match of 1.077 : 1.00 at 144.150 mhz.  Worse case was transmit at 147.995 mhz which was 1.199 : 1.0.   The new matching system worked better than I expected.

Jon working on Tower

Jon and I had to lift the mast with the two VB-28FM antennas, plus a Diamond V2000A up with mechanical lift.  Besides the weight of the antennas and tube (1.500″ OD, 1.2500″ ID, Structural Steel), the total length of the assembly was 26.3′.  6.0′ of the tube went through the thrust bearing to the Ham-IV rotor.

After Jon went through the exercise of properly torquing the bolts, we brought up the rotor control box and checked to make sure it cleanly rotated 360-degrees, and the meter was accurate.

The trust bearing used was a Yaesu model HG-065.  The plate you see which the bearing sits on was custom made for the top of the American type 1 tower.  (Note American towers do not mate with American type 2 or Rohn 25 towers).   Mounting hardware was subbed with Stainless Steel bolts, washers, and nuts.

After making the tower top plate it was taken to Elida Metal Coating company and given an outdoor, thick Power Coating.   Black was chosen so in the winter any snow or ice on the plate would receive the maximum amount of warmth from the sun.

The two VB-28FM antennas are separated by 1 wavelength at 144.1500 mhz.    The top VB-28FM did not need any major separation from the Diamond V2000A as analyzer readings showed very minimal inter-reaction in the 2 meter band, and no effect in 6 meters or 70 cm band.

The coax jumpers down to below the top of the tower were RG8/F with Amphenol Type 1, 50? gold pin.  They will mate to a panel with Andrew L1PNF-BH connectors which are terminated to Andrew FSJ1-50 transmission line which goes to the room with my ham equipment.

The FSJ1-50 is roughly the same O.D. as RG-6 coax, so I was able to use standard CATV plastic staples to secure the line in the attic.  This is a crush-proof type of staple used in cable TV installation.

The transmission line is grounded at the top of the tower just below the top plate, at the bottom of the tower where it transitions into the attic, and then at the RF patch in the radio room.  Before the coax enters into the attic it makes 9 loops of roughly 7″ diameter for lighting mitigation.

Analysis of return loss and VSWR over 4 mhz paralleled the readings made on the ground.

One important note… on my Yaesu FT-897D, there is one RF connector for 2 and 70 CM operation.  However, 6 meter comes out on the HF connector.  This means the feed from the V2000A antenna must go through an RF switch which allow you to select the correct radio port to the antenna.

 

ROLL YOUR OWN

I have every reason to believe that someone with some time, and ability to work with aluminum could easily built this antenna.  Page 2 of the VB-28FM manual provides measurements.  However I would advise you build a matcher like I did as the method used by the manufacturer us poor at best.

You should never leave coax open at the end in the outdoors as the capillary action will cause water to migrate up the shield and center conductor.  Also, don’t go on the cheap and use at hardware.  Spend the money for stainless steel so you get years of uninterrupted use.

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NOTES

1). McMaster Carr. http://www.mcmaster.com (330) 995-5500
2). Mouser Electronics. http://www.mouser.com (800) 346-6873
3). RF Parts. http://www.rfparts.com (800) 737-2787
4). Manual for the Hy-Gain VB-28FM in this article.  Manual for the larger Hy-Gain model VB-214FM.
5). Diamond V2000A Manual, present manufactured.  Use only their hardware as it’s metric.


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