Power rating and SWR of Alpha Delta DX LB

[KA2PTE]

I was given one of these multi band antennas a while back and after reworking the loading coil connections
to the radials, its functioning much better.

The antenna is basicly a 40m dipole with longer radials added and loading coils to make 80 and 160m possible towards the end of the antenna.
There is an LB PLUS out that is different than this, but has some similarity.

The plots for mine on 40 look as intended, but the SWR on 80 and 160 are kind of on the high side and wonder if this is to be expected?
I have plots for the antenna taken with a nano VNA here:

http://www.mediafire.com/file/t6vjlv9zkx7n89f/DX_LB~Nov_12.zip/file

Also am curious about the power ratings for the antenna as the company provided none. I am told probably the 40m section could handle legal limit, but as we head to 80 and 160, the loading coils come into effect for those bands. Apparently the loading coils are designed to block
out the ends of the antenna at 40m and I guess as you head down towards 80m, the blocking effect of the 1st coil becomes less and adds length,
and so fourth for the 160m section. I believe coils reduce efficiency, and its understandable as this is a compromise antenna, but how would we go about figuring out the max power to run in this antenna for the 80 and 160m band?




 

 

[kd1nw]

Hi,

The info is in the instruction sheet.
http://dxsupply.com/produktfiler/DX-CC,%20DD,%20EE,%20LB,%20LB%20Plus%20instructions.pdf

Make sure the SWR is 1.5 : 1 or less for max pwr rating. I used my DX-CC with a Globe Champ 300 at 200 watts carrier with no issues but your mileage may vary as they say.

•Model DX-CC: 80 thru 10 meters, 1000 watts CW/PEP, ICAS duty cycle.
•Model DX-DD: same for 80 and 40 meters.
•Model DX-EE: 40 thru 10 meters, 1000 watts CW/PEP, ICAS duty cycle.
•Model DX-LB: 160, 80 meters, 600 watts CW/PEP; 40 meters, 1000 watts CW/PEP, ICAS duty cycle.
•Model DX-LB Plus: same as above for 160 and 80 meters, and same as Model DX- CC on 40 thru 10 meters.
IMPORTANT NOTE: All models shown above are limited to 250 watts RF output for continuous key down modes like RTTY to prevent overheating of components.

I hope this helps!

73 - Kevin KD1NW

[KA2PTE]

Thanks, great document Kevin, never seen that one before.

With my SWR high for some reason on 80 & 160 anywhere from 3-4,
I can get it down with the Dentron MT-300A tuner, but I am told it ought to be closer to a
2.5 or so if I remember right.

Today I did another test on 80m and I have 2.76 swr at 3830kc where back on Nov 12 in the linked file,
its 3815kc at 3.13 swr.

On 160m today I have 3.49 swr at 1946kc and in Nov it was 4.14 at 1936kc.

I didnt check 40m because its always been very flat and well below 2 for the most part except on the upper part of the band.

Strange how thats moving lower in SWR and up up in frequency about the same on each band without touching anything. Wonder if its a bad coil or coil connection - but we went through all of them and I repaired alot of bad
connections from the coils to the radials, and replaced them with ring terminals, including the feedpoint.

Im wondering if a coil connection is marginal, does it sorta start to act like an OCF dipole, as one radial is seen as shorter than the other.

[kd1nw]

Hi,

These antennas are somewhat sensitive as to how you have installed them. Especially for the bands after the resonator such 80 and 160. Things like how high up they are, are they running through trees or close to metal objects, are they configured as inverted v or regular dipole.. they might even change a little bit if the ground has been soaked etc. Also make sure the wires before the resonator are well separated in the stand offs. They don't have to be pretty but you don't want the wire close to each other. Once it's all worked out the antenna works pretty good, it's just a bit of a pain with those wires fanned.. they are cumbersome to deal with. I would expect you to be able to get a low swr somewhere on 80 meters but I bet this antenna would be touchy on 160. If you get a low swr there it will be narrow, like pretty much one frequency.

73 - Kevin

[KA2PTE]

Still have this antenna up, and working well....its up in a "Vee" type
config, so its got some vertical polarization to it.

There is a "Plus" version DX eng makes now where they turn the 40m dipole section
into a fan dipole by adding more radials for 20 and 10. The description on their site says:
"coverage from 160-10m". But does this include even the WARC bands?

Mine is just the plain LB, no fan radials, but I want to try adding radials to it to get more band coverage.
Would it be more efficient to include radials for the WARC bands, plus 20 and 10 ? I also work 6m and 2....
but I think that would mean 7 additional sets of radials total.

I am curious too that if the new radials are mounted above the main 40m section, would they act as directors
and improve signals on the lower bands, kind of like how a beam works?

[KA2PTE]

Had to take the LB down a while ago due to the tree being a problem.

I am converting it into a fan dipole for 60/17 and 6m and re-using the radials
fo rthe 60m section. Noticed there are 2 scorch marks on the radial
between the loading coils on one side. One is all the way thru, the other
you can just make out some discoloring and bubbling.

Was curious if this is the usual evidence of RF overload, or could the burns be
from someone holding a lighter to the radial?