The Quagi Revisited
With interest in 222MHz being tweaked and peaked by the W7BAS transverter kits (w7bas.blogspot.com), it’s reasonable to expect there will be quite a bit of interest in a simple and easy to build antenna for the band.
Dave (W6OAL) and I were on one of our in shop sessions and ran out of things to do. We decided a 222 antenna based on some recent research into close spaced cubical quad and wider spaced linear directors could work well together. We also determined that we had already learned the lessons of cutting off the household broom handle to use as an antenna boom and would not repeat that domestically challenging move. So a metal 3/4″ X 3/4″ X 48″ aluminum stock section would be the foundation upon which this antenna would be built.
Dave set up a test range in the shop and we proceeded to build the driven element (54″ loop with one inch on each side bent down to attach to the BNC (F) receptacle.), and the reflector (59″ loop with 1/2″ overlap soldered together.) The spacing would be closer than the typical quad to maximize the gain from these two elements. Approximately 0.11 wavelength yielded the greatest field strength on the spectrum analyzer receiver in the test range so the quad elements were to be 5 1/4″ from (DE) driven element to (R) reflector. A pair of 1/4″ wood dowel rods 19″ long was inserted through holes drilled in the boom and supported the driven element. A BNC (F) receptacle was soldered directly to the 1″ “ears” bent from the DE. The reflector was supported in a similar fashion with a pair of 1/4″ wood dowel rods 21″ long. The elements were held in place with tie wires and a small amount of Gorilla Glue was applied to illustrate how sure we were that our calculations were perfect. . . . We now had a close spaced two element quad on 222 and were ready to fill out the four feet of boom with linear elements.
We calculated the first director should be 24 1/2″ long and cut a piece of brass rod to this length. The director was mounted through the boom 10″ from the DE and a set screw was employed to keep it in place. The spacing was once again determined by maximizing field strength as displayed on the test range.
The remaining elements were also cut to 24 1/2″ rather than being tapered because there is not much operation beyond a few tens of KHz either side of 222.1MHz. The second director (D2) was placed 12″ from D1 and D3 12″ from D2. There was about 5″ remaining on the four foot boom but we really didn’t gain anything by placing another director that close so the space was left for mounting hardware.
Let’s consolidate those measurements; The reflector is number 12 bare wire 58″ around cut to 59″ to allow for 1/2″ overlap installed in a diamond orientation. The driven element is number 12 wire 52″ around cut to 54″ with one inch bent down to connect to the BNC connector at the bottom of the diamond. The three directors are 24 1/2″ brass rods. D1 is 10″ from the DE. D2 is 12″ from D1 and D3 is 12″ from D2. Quarter inch dowel rod was used to support the DE (19″) and R (21″). These elements were mounted on a four foot 3/4″ X 3/4″ aluminum square stock section.
So, you are probably wondering how this worked. We decided a real on the air test would be the best way to determine if this was a working antenna so off to my QTH some 80 miles from Dave’s place the new antenna went. We established a baseline with a horizontal omnidirectional antenna and connected the revisited quad. The received signal went up approximately 10dB when Quagi2 was put in line. The front to back is greater than 20dB and the pattern seems to be quite clean. We declared success and the antenna can be heard on Tuesdays at 8PM for the 222.1 activity night.
When you get your new transverter built and want to get on the air ASAP with some gain this antenna can provide that critical last element to let you hear and be heard.
A picture is worth a thousand words so this should answer any remaining questions. Yes, the loop is directly fed and SWR is around 1.2:1 without a matching stub.
This antenna fills the bill for an effective, simple, low cost, compact, and inexpensive way to get on 222.1. I look forward to hearing you on the Tuesday activity night.
222 Quagi Revisited
The Quagi Revisited