WE RECENTLY RE-DESIGNED THE PHONE –CW RELAY AND COIL HOUSING AND GENERAL
ASSEMBLY. This was done to make manufacture easier and to allow customer modification and main-
tenance. We now use a fiberglass enclosure that can be opened for inspection, repair or modification.
Looking inside the housing you will see that we have provided two holes in the coil leg that attaches to
the relay. Generally the easiest way to move the frequency of the element when the coil is engaged, is
to change the inductance of the coil by spreading it. Quite a wide range of inductance can be achieved
by lengthening or shortening the coils. They are set to be just under 2.5 uHy from the factory. By shift-
ing to the other holes in the coil legs, the inductance can be dropped to about 2.3 uHy. This will shift
operation up the band about 50 kHz. You may also have to physically open the coil since it is springy
and make sure all the turns are evenly spaced. Larger movement in frequency can be achieved by re-
moving turns, however you should do some calculations first or contact the factory to avoid seriously
degrading the bandwidth, or performance of the antenna. The antenna has been modeled in Brian
Beezley’s AO “PRO” ,version 6.5. Linear loading will not necessarily model correctly in NEC based
programs. AO is
Mininec
based and does much better at modeling parallel wires than NEC.
What about coils in the place of the linear loading? Several hams have had another group modify our
Yagi to eliminate the linear loading and convert to coils. The boom is also lengthened by about UP TO
18 feet. This results in a gain improvement of .8-.9 dB and this is not due to the coils, but to the added
boom length AND NARROW BANDING.. We have modeled both coils and linear loading and when all
other parameters are equal, the performance is virtually the same. One big But remains however. The
“Q” of the coils used must be over 600. This is very difficult and expensive to do. For those of you
who have structural or local weather concerns, you should know we are planning on producing a coil
version of the 80M3. We are doing this carefully and slowly. We are also planning on offering a longer
boom version of the 80M3. As always, we like to make changes in such a way that past owners can
upgrade. We will continue to review customers desires and at some point, if some want or need coils or
a longer boom, or both, we will make what our customers request.
We just don’t want you to be misled by a few random, uncontrolled on the air tests that show one an-
tenna to be better than the other. So many parameters are at play that it is easy to come to the wrong
conclusion. Height above ground, local terrain, location in the world or in the United States, feedline
loss and of course, the RF power delivered to the antenna all can have massive effects on test com-
parisons.
Enjoy your 80M1L and call me if you have questions or concerns.
73, Mike Staal, K6MYC
ADJUSTING / CUSTOMIZING YOUR 80M YAGI
