While you might get into a conversation about why Mosley at all, or why
traps at all with newer antennas from any number of manufacturers that
either eliminate traps or minimize them, I will stay away from that.
The lengths of elements on a trapped element are HUGELY dependent on the
characteristics of the traps. The ten meter (inner) traps on an element
will be parallel resonant on ten preventing significant coupling with
the rest of the element. This makes the ten meter elements most like
full size beam elements.
On fifteen the outer traps will be parallel resonant effectively
removing the tips from the equation, but the ten meter traps now appear
as a series coil, the amount of inductive reactance depending on the
trap design, INCREASING the electrical length of the aluminum inside the
On Twenty both inner and outer traps appear as series coils. This makes
the electrical length of the element considerably longer than the
physical length on 20.
The efficiency of the traps can have an effect on performance.
Particularly if one of the traps is bad. This may show up in obvious SWR
if the trouble is in the driven element, but effects on SWR are much
more muted if the trouble is in the director or reflector. Further,
which bands will show bad depends on the exact nature of the trouble.
Some people have been known to deal with an SWR problem in a new trapped
beam by adjusting the DE to get the **SWR** down, mistakenly equating
SWR with performance. All they did was to MASK the clue to the REAL
problem, elsewhere in the beam, by adjusting the DE.
You need an original construction manual, go over it inch by inch, and
verify that the traps are all OK, the right traps, in the right place,
and all the tubing lengths are correct. Anything else is a snipe hunt.
You may find that the antenna stinks, even if it's right on spec
Won't be the first time that has happened to someone.
73 & Good Luck.
Guy Olinger, K2AV
Apex, NC, USA
----- Original Message -----
From: "Dennis Schaefer" <email@example.com>
Sent: Monday, October 08, 2001 8:57 PM
Subject: [TowerTalk] Mosley CL-33
> I have a Mosley Classic-33 (CL-33M) triband antenna that doesn't seem
> have the "punch" that it should. It replaced a PRO-57 and the
> difference is like daylight and dark (why did I replace the PRO? Long
> story involving modifications for the WARC bands....). On 20, 15,
> 10 meters, I could bust the biggest pileups with the PRO. The PRO has
> foot boom and 3 active elements on each band. The CL-33 has an 18
> boom and 3 active elements on each band. Maybe a little difference
> gain, but not daylight and dark... The new and old antennas are on
> same tower at exactly the same height (56 ft) with the same feedline.
> SWR on the CL-33 looks normal, and it seems to have normal F/B on 20
> 15, but only about 5 - 10 db on 10 meters. I attributed that to the
> wide spacing on 10. However, it just doesn't get out. DXpeditions
> now difficult to work, even running 600 watts out. I usually got 'em
> the first day with the PRO-57, which wasn't that great an antenna
> with others.
> While studying the instructions I noticed the reflector on the CL-33
> feet long (phone setting). The driven element is approximately the
> length (a foot longer with CW setting) but that is explained by the
> that the classic feed system is a capacitive feed and requires a
> I got curious when I looked at some other Mosley manuals. The
> a similar antenna, but with 4 elements. The directors (and
> D.E/reflector spacing) are within a couple of inches of the CL-33
> D.E. is shorter due to direct feed) but its REFLECTOR is nearly a
> A HALF longer than the CL-33's! The reflectors on the TA-34XL and
> CL-33 have identical 25 and 15 turn trap coils, so this isn't the
> The other manuals I have are for the PRO and the CL-36, and they
> have a tri-band reflector.
> Does anyone have any insights on this? Reading the archives tells me
> is supposed to be one of the best antennas Mosley ever made and I
> see a single complaint. Where should I start in trying to diagnose
> (On another subject - If anyone has a TA-32 manual, I would appreciate
> reflector dimensions and number of trap coil turns - I'm trying to
> 2-element tribander out of spare Mosley parts).
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