Category Archives: Antennas

Articles about Antennas, Feedlines, Towers and related equipment. Fixed, Portable and Mobile Antenna Articles are included.

Antennas: Where There is a Will…

The 2017-2018 contest season featuring the “big four” events (CQ WW SSB, CQ WW CW, ARRL DX CW and ARRL DX SSB) recently came to a close with a resounding thud. The Solar Flux Index seems to have flat-lined below 70 as we bottom out in the current sunspot cycle. This translates to little DX above 20 meters. For 40 meters and down to Top Band, however, no sunspots are good. I remember the fun I had during the last cycle bottom when I roamed Top Band as an avid bottom-feeder pulling in choice DX from the Pacific and Asiatic Russia. I had a pair of K9AY loops oriented in a cross configuration to enable me to select the four cardinal directions. The loops worked wonders at reducing the high noise levels on 160 meters. They also worked well on 80 meters during noisy conditions.

Alas, being in the land of CC&R and clandestine antennas (read: low, short wires and verticals), Top Band operation is non-existent. Yes, there are some diehards here who have a convoluted run of wire that is heavily loaded and fed with a tuner struggling to make a match. Working FL, GA, AL, Cuba and the Bahamas becomes the high point in a Top Band contest. If 160 meters is not practical, perhaps there is something to be done for 80 meters.

I think I may have found a way. About a month ago while the family and I were on a cruise, I noticed a three-masted sailing vessel at one of our ports of call. I was intrigued by the mess of ropes and sails on the ship and wondered how the sails were hoisted. Each sail is attached to a series of collars that ring the mast. As a sail is hoisted, the collars ride up the mast, much like a shower curtain that is pulled close. As my few brain cells coalesced on the concept, it occurred to me that I could do something similar with my PVC flagpole. In lieu of a sail, I thought of an extendable fiberglass mast like those usually found at hamfests. The base for the mast would be two or three feet away from the flagpole to hide it from direct view of the street. My thought is to erect a 40-foot mast using the sailing vessel approach to guy the mast against my flagpole. This approach would provide a support near the 22-foot top of my flagpole with a couple of guy ropes off the top of the mast. The mast to flagpole connection would be fixed at the 22-foot point with the mast.

So what kind of antenna will go on the mast? I did some modeling with EZNEC to see what an inverted V for 80 meters would look like. Each leg would be about 56 feet long if the anchor points are out 40 feet from the mast. First look at the antenna should reasonable performance – above 3900 kHz; not an area of the band I care to operate in. I added some inductive loading at the feedpoint to electrically lengthen the antenna. I was able to get good SWR performance for the lower 100 kHz which encompasses the CW and digital parts of the band.

(Note: The casual observer may notice that a 40-foot structure in a CC&R territory is begging for a visit from the local vigilantes. This problem is adequately mitigated by the fact that 80-meter propagation favors darkness so I would not raise the antenna until after sundown. I would have it down before most folks get through their first cup of coffee.)

Now that I have a sporting chance with something other than the fat coil plus 3-foot wire that I currently have with my 6BTV vertical for 80 meters, I needed to come up with a better receive antenna. While power-washing the moss and mildew off the side of my house I experienced another epiphany as well as a tired back. My house has vinyl siding, good for growing moss and mildew but it also non-conductive. I had been thinking of a K9AY loop but the loop needs a vertical support and has to be away from large objects such as a house. I looked at other receiving antennas such as the flag and pennant antennas, so called because of their physical resemblance to said shapes. These antennas have a length similar to the K9AY loop and function the same way, i.e. the intended receive direction is the feedpoint and the opposite leg is terminated in a non-inductive impedance. The antennas are mounted about 20 feet at the top point so that the lower leg allows clearance for people and critters.

While I am not able to raise a receiving antenna up 20 feet, why not slap in on the side of my house? I have an expanse of siding about 32 feet long by 8 feet high without windows where I could install a pennant antenna. The antenna vertical section would be about 8 feet at the top and about 0.5 feet above the ground at the bottom. The sloping parts of the pennant would run to the front corner of the house where the termination/junction point would be conveniently hidden by shrubs. The feedpoint, located halfway up the vertical section, would be hidden along the edge of one of my bedroom shutters. I can use yellow wire for the pennant to match my house color to add more stealth. If nothing else, I can always pass the pennant off as artwork on the side of my house. Many homes in The Villages has decorative metal artwork on the walls so I would fit right in.

So how would a “slap-on” pennant work? Back to EZNEC for some more modeling. I checked the antenna patterns for a frequency of 3.550 MHz and a termination resistance of 900 ohms. At an elevation angle of 35 degrees, I have a gain of -31.4 dB and a front-to-back (F/B) of 21.0 dB. I compared the performance of my pennant with a design by K6SE that has a 14-foot vertical section and is 6 to 20 feet above the ground. Total wire length is within a foot for both antennas. At 3.550 MHz, the K6SE pennant shows a gain of -26.6 dB and an F/B of 21.6 dB. Not bad.

To compare my pennant design to the K9AY loop, I ran patterns for 1.8 MHz since I had data for the K9AY loop for 160 meters. The K9AY loop sports a gain of -23 dB while my pennant manages a gain of -41.9 dB. It is likely that such a difference will also be the same for 80 meters. It is a good thing there are preamps available.

Now that I have the will, I just need to find the way to make it happen in time for the next contest season.

Ed, K2TE

Upgrading 2.0 Satellite Station for an ARISS Crew Contact

We have been working with Hudson Memorial School near Nashua, NH to prepare for a possible ARISS Crew Contact. The ARISS folks work with schools and their Ham Radio helpers to prepare for these contacts. ARISS provides recommendations for ground station equipment to help ensure a good experience for the students. The ground station recommendations provide a solid set of specifications to support communications with the ISS on the 2m band. The recommendations include things such as:

  • A requirement to build both a primary and a backup ground station
  • Radio and power specifications (a 200W amp is recommended)
  • Antenna specifications including recommendations to provide for switchable LHCP and RHCP
  • Computer controlled azimuth/elevation positioning of antennas to track the ISS
  • Use of a receive preamplifier at the antenna

You can read more about our ISS Contact upgrade plans via the link below…

Source: Upgrading our 2.0 Satellite Station for ARISS Contact

Fred, AB1OC

Portable Satellite Station 3.0 Initial Contacts

With the construction of our portable satellite station 3.0 complete, we’ve been looking forward to an opportunity to test the new setup. We chose the Nashua Area Radio Society’s recent…

Portable Satellite Station 3.0 Antenna System
Portable Satellite Station 3.0 Antenna System

Source: A Portable Satellite Station Part 6 – 3.0 Station Initial Contacts | Our HAM Station

Our next generation portable satellite station is complete and we tested it during our recent Tech License Class. We discovered a minor issue which was easily sorted out. The new antenna system includes switchable circular polarity and has performed really performs well during the first 50 or so contacts made using the 3.0 station. You can read more about the new station and the initial tests via the link above.

Fred, AB1OC

Get ready for Antenna Modeling

Antenna Modeling
EZNEC Example

The March Tech Night (March 13, 2018) will have an introduction to antenna modeling by me, Scott, NE1RD. I’ll begin by going through some antenna theory and then proceed on to the NEC-2 software and its popular front ends EZNEC and CocoaNEC. (Both the evaluation/demo version of EZNEC, and the Macintosh-based CocoaNEC are free.) LINUX users should consider getting Andy (KB1OIQ) Stewart’s Andy’s Ham Radio Linux suite. The main concepts you’ll learn will apply equally well to any of these programs.

Please download the antenna modeling software for your platform,  and download the slides for this presentation from the Tech Night web page. The slides have a lot of detail on them, and it will be much easier to see the subtleties on your own screen.

So, bring your laptop with software and slides, and we’ll have you modeling antennas by the end of the evening. See you there!

Scott, NE1RD