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[VE3HLS]

Hi Group,

I operate a remote station that consists of an IC-7300 and a Hustler 6-BTV trap vertical. The vertical was tuned to provide best SWR in the FT8 portion of the bands.  I can fine tune things with the 7300's built in autotuner to keep the rig happy.  I use it daily and SWR is never greater than about 1.2:1 on all HF bands, until this morning.  I went to operate on 30m and the SWR was 5:1.  All other bands were OK as before.

My understanding of multiband trap antennas is that a trap will pass signals to lower bands but not higher bands.  In other words if the 30m trap became damaged then I'd have problems on 40m and 80m as well, but I don't.  20, 15 and 10m are unaffected. 

This behavior on only one band baffles me, and challenges my notions on how trap antennas work.

Has anybody had a similar problem, or have any information that I appear to be lacking?  Any help would be gratefully received.  In the mean time, I have emailed my remote station's "host" and asked him to make a quick visual inspection to see if the antenna looks OK.

73 and thanks in advance.

Ken Alexander  VE3HLS

[N4UFO]

My understanding of multiband trap antennas is that a trap will pass signals to lower bands but not higher bands.  In other words if the 30m trap became damaged then I'd have problems on 40m and 80m as well, but I don't.  20, 15 and 10m are unaffected. 

Hey Ken!  Long time!  How are things? Still overseas or back in NA? I moved cross country and have not been on the birds much, but I have plans... always plans and more things to do. I'm sure you know how that goes. 

I have had a couple Hustler verticals, generally good antennas. As to your understanding, mine is different. Simply put, the trap will pass everything except the band it is TUNED FOR and designed to trap. It will pass bands on either side, so as far as I know, 40m & 80m should still work.

That said, you mention that SWR is normally 1.2:1 on all bands. Is that a wide dip across entire bands? If so, that is not necessarily a good thing. With a proper ground mounted vertical, first thing is that the normally lowest SWR is 1.4:1 although some tweaking can get it lower. But the 'dip' should not be terribly wide. If it is, then that likely means a poor ground that is not efficient. In other words, the SWR may be "good" because the antenna is losing power to an inefficient ground setup. Many hams install these antennas on a pipe with no radials (including me early on) and see a nice low SWR across all of the bands and think, 'That's great!'. But alas, in fact no, that means an inefficient antenna that is warming the ground instead of radiating. Adding radials will sharpen the curve and more energy will be radiated into the sky & towards the horizon instead of into the ground.

Sorry if that is more info than you bargained for. Hard lesson on verticals, but your on air performance may thank me later. 

73 & Good luck!  Kevin N4UFO

[WB6BYU]

A tree branch laying against the antenna near
the 30m trap could do that.  The impedance is
high at that point on 30, so the antenna is very
susceptible to detuning from nearby objects,
but less so on other bands.

Generally the problem would be easier to
evaluate if we knew the SWR on each band
without using the autotuner, both before and
after the failure.  It is quite possible that the
SWR curve has shifted on other bands as
well, but still within the range of the tuner.

[VE3HLS]

My understanding of multiband trap antennas is that a trap will pass signals to lower bands but not higher bands.  In other words if the 30m trap became damaged then I'd have problems on 40m and 80m as well, but I don't.  20, 15 and 10m are unaffected. 

That said, you mention that SWR is normally 1.2:1 on all bands. Is that a wide dip across entire bands? If so, that is not necessarily a good thing. With a proper ground mounted vertical, first thing is that the normally lowest SWR is 1.4:1 although some tweaking can get it lower. But the 'dip' should not be terribly wide. If it is, then that likely means a poor ground that is not efficient. In other words, the SWR may be "good" because the antenna is losing power to an inefficient ground setup. Many hams install these antennas on a pipe with no radials (including me early on) and see a nice low SWR across all of the bands and think, 'That's great!'. But alas, in fact no, that means an inefficient antenna that is warming the ground instead of radiating. Adding radials will sharpen the curve and more energy will be radiated into the sky & towards the horizon instead of into the ground.

Hi Kevin!

Nice to her from you!   I haven't worked anyone via satellite since 2018, but I do listen from here in Thailand occasionally.  I want to set up an SDR at my host's QTH and see if I can work that satellite on HF/UHF with the uplink in the 15m band since I already have half the equipment I need.

Anyway, I can tell you that I can only operate in a very narrow section of the 80m band, centered around the FT8 portion 3.583 or something like that.  I can work some CW but going up into the phone portion is a little too far away.  On the other bands the 7300's tuner will usually give me enough latitude to work down to the bottom the band and further up, though I rarely use phone.  The 6-BTV is a replacement for an antenna I installed originally that didn't work very well.  I bought it from DX Engineering and had it shipped to a ham friend who volunteered to install it and set it up for me.  He did a good job but I don't know how many radials he laid down.  "Not that many" is my guess, but I really don't know.  My host is on a suburban property; surprisingly quiet but the lot is only about 35 ft wide and his back yard is about 30 ft deep.  Not a lot to work with.

I'll try install bunch of short radials next time I'm back but no idea when that will be.

73 for now,

Ken

[VE3HLS]

A tree branch laying against the antenna near
the 30m trap could do that.  The impedance is
high at that point on 30, so the antenna is very
susceptible to detuning from nearby objects,
but less so on other bands.

Generally the problem would be easier to
evaluate if we knew the SWR on each band
without using the autotuner, both before and
after the failure.  It is quite possible that the
SWR curve has shifted on other bands as
well, but still within the range of the tuner.

A tree branch laying against the antenna near
the 30m trap could do that.  The impedance is
high at that point on 30, so the antenna is very
susceptible to detuning from nearby objects,
but less so on other bands.

Generally the problem would be easier to
evaluate if we knew the SWR on each band
without using the autotuner, both before and
after the failure.  It is quite possible that the
SWR curve has shifted on other bands as
well, but still within the range of the tuner.

Hi,

I'm inclined to believe the tree branch theory.  I had my host check the antenna to make sure it was OK.  He sent me a photo showing it is near some branches.  I also re-checked the SWR on all bands just now with the following results (note that 30m appears to be OK but now 80m has problems.

Band     No Tuner     With tuner
80m        4.5:1           4.5:1
40m        1.5:1              1:1
30m           3:1           1.1:1
20m           2:1              1:1
15m         2.5:1             1:1
10m         1.5:1             1:1

It seems a different tree branch is rubbing up against the antenna, on the 80 section.  I'll check it again this evening to see if things change again.
Any additional thoughts?

73 and thanks!

Ken  VE3HLS
 

[WB6BYU]

The 80m bandwidth will be pretty narrow, and
strongly affected by the capacitance between the
stinger on the 80m resonator and surrounding
objects.  I e watched the SWR vary on a “Hamstick
Dipole” due to a branch blowing in the wind 5’
away.

A useful check would be the 80m SWR across
the band, to see what range of frequencies
it will cover.  You may find that it changes with
the weather.

[K1KIM]

I have a 5-BTV and the issue with 80M whip having a very narrow bandwidth is directly related to the length the whip is cut to.

The 80M on the 5 and 6-BTV is really a very poor offering unless you are satisfied with picking a 20kHz portion or swapping whips for each area of the band you go to.

Mine is cut for 3.885 which is the local net.

I wish I had bought the 4-BTV years ago, as now I have a resonant 80M wire that covers the entire band at a very acceptable SWR with my tuner.

In my opinion it is a bad choice of antenna for 80M.

I don't operate on 30M so I can't offer any comment there.

[VE3HLS]

The 80m bandwidth will be pretty narrow, and
strongly affected by the capacitance between the
stinger on the 80m resonator and surrounding
objects.  I e watched the SWR vary on a “Hamstick
Dipole” due to a branch blowing in the wind 5’
away.

A useful check would be the 80m SWR across
the band, to see what range of frequencies
it will cover.  You may find that it changes with
the weather.

The 80m bandwidth will be pretty narrow, and
strongly affected by the capacitance between the
stinger on the 80m resonator and surrounding
objects.  I e watched the SWR vary on a “Hamstick
Dipole” due to a branch blowing in the wind 5’
away.

A useful check would be the 80m SWR across
the band, to see what range of frequencies
it will cover.  You may find that it changes with
the weather.

Just got in the shack.  'll try on 80m nwo before I get busy doing other things.

Thanks,

Ken  VE3HLS

[VE3HLS]

A useful check would be the 80m SWR across
the band, to see what range of frequencies
it will cover.  You may find that it changes with
the weather.

Hi,

OK, here's a scan across the 80m band.

Freq     No Tuner     With Tuner
3510     1.9:1            1:1
3520     1.9:1            1:1
3530     1.7:1            1:1
3540     1.6:1            1:1
3545     1.6:1            1:1
3550     1.6:1            1:1
3555     1.6:1            1:1
3560     1.6:1            1:1
3565     1.7:1            1:1
3570     1.8:1            1:1
3573     1.8:1            1:1  FT8 Frequency
3575     2.8:1            1:1
3580        3:1         1.1:1
3585     4.5:1            5:1
3590        5:1            5:1

Everything makes sense to me except for how it behaves below the design frequency (3573 kHz).  That was unexpected.

73,

Ken  VE3HLS

[VE3HLS]

I have a 5-BTV and the issue with 80M whip having a very narrow bandwidth is directly related to the length the whip is cut to.

The 80M on the 5 and 6-BTV is really a very poor offering unless you are satisfied with picking a 20kHz portion or swapping whips for each area of the band you go to.

Mine is cut for 3.885 which is the local net.

I wish I had bought the 4-BTV years ago, as now I have a resonant 80M wire that covers the entire band at a very acceptable SWR with my tuner.

In my opinion it is a bad choice of antenna for 80M.

I don't operate on 30M so I can't offer any comment there.

Hi,

Thank you for the comments based on your experience.  I'm satisfied with my 6-BTV.  I'm retired and live in Thailand so my remote setup is twelve time zones away.  I don't have a lot of opportunity to tweak or experiment with other antennas.  My host's back yard is also quite small: 30' x 35'.  Despite that, I have WAS (digital) on 80m and am well on my way to DXCC 80m (mixed Digital/CW). 

Next time I'm back in Canada I plan to add more radials to the antenna system.  Another ham installed the 6-BTV for me;  I don't even know how many radials there are.  Not many, I think.

73 and thanks again!

Ken  VE3HLS

[AI5BC]

I use it daily and SWR is never greater than about 1.2:1

That's a problem and it is telling you that you do not understand the antenna to start with.

[VE3HLS]

I use it daily and SWR is never greater than about 1.2:1

That's a problem and it is telling you that you do not understand the antenna to start with.

Care to enlighten me, or are put-downs the limit of your involvement?

73,

Ken  VE3HLS