Here are links to photos of the A3 TC 15m trap, the original Cushcraft
version circa 1992 and the recent MFJ one:
sdellington.us/hr/TC_CC1.jpg
sdellington.us/hr/TC_MFJ1.jpg
Note the two pop rivets in the CC trap, missing from the MFJ one. There
are two more rivets on the other side. The extra screw in the CC trap is
one I added. Note also that the wire on one end of the MFJ coil is
wrapped the wrong way. Originally, both terminations looked much worse.
Later, I wrapped both the right way, and added SS flat washers. I also
fixed that almost shorted turn.
The MFJ trap has 4 fewer turns than the CC trap, though the resonance is
about the same. It looks like the MFJ coil form is slightly larger.
I don't like to bash MFJ, as I think they provide a useful service to
the ham radio community, but I do wish they paid more attention to QC,
especially for antennas, installation of which involves a lot of work
and expense.
73,
Scott K9MA
On 9/12/2019 13:22, K9MA wrote:
I recently ordered some replacement traps for my old A3S. One was
defective, so I took it apart. I was appalled at the poor quality.
While the original traps had several pop rivets, in addition to the
coil screws, connecting the tubing to the plastic insulator, the MFJ
version had only the two screws in the very end of the tubing. The
coil wires were sometimes wrapped the wrong way around the screws, and
some of the screws weren't even tight. Where the original coil was
coated with some kind of thick lacquer, the MFJ ones were bare.
The moral of the story is don't even think about going to the trouble
of putting up an MFJ/Cushcraft beam without taking apart all the traps
and fixing the above problems.
73,
Scott K9MA
--
Scott K9MA
k9ma@sdellington.us
_______________________________________________
_______________________________________________
TowerTalk mailing list
TowerTalk@contesting.com
http://lists.contesting.com/mailman/listinfo/towertalk
|