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Author Topic: 1.5K-FA ATU  (Read 2579 times)
KD2JVX
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Posts: 2




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« on: March 19, 2018, 01:07:10 PM »

Just got a Expert SPE 1.5K-FA.  Having the following issues with the tuner (ATU) - anyone else?

1. I have an EFHW-8010 Multiband End Fed Half Wave Antenna which is resonant Half wave on 80m (3.5MHz) therefore also resonant on second, third and fourth harmonics etc.  It has a high impedance feed point.   The native ATU in the IC-7100 and 7300 seems to recognize this and will not try to tune.  I have low SWR on all those bands (less than 2).  It is rated for 1.5k watt.  The 1.5K-FA seems to try to tune it.  It will not function on 80m when I had no problems with 80 before.  Is there a solution to this?

2. I also have a full size G5RV. I used an MFJ-939.  It would tune anything higher in frequency 80 and over.  The G5RV should be resonant at 20m.  The 1.5K-FA ATU can not find a match for this antenna on any band including 20m.  Strange.  Is there a solution to this?

k2jvx
Thanks and 73
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N7EKU
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Posts: 1045




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« Reply #1 on: March 19, 2018, 02:39:35 PM »

Hi,

Are you using any common-mode chokes in your system?  At lower power levels, the magnitude of common-mode current may not be high enough to bother your tuners, but at high power it can become a big problem.

73,


Mark.

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Mark -- N7EKU/VE3
VK3BL
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Posts: 1790


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« Reply #2 on: March 19, 2018, 10:50:29 PM »

The built in ATU is only designed to match ~3:1 mismatches; the same as most transceivers.

Its really just designed for 'trimming up' mono band antenna such as a Yagi on band edges.

If your radios won't match the antennas, and the amp won't either, the simplest explanation is the antennas are presenting a higher mismatch.

My G5RV, which admittedly I never 'tuned' for my specific installation - I just slapped it up there - is nowhere near the theoretical specs published online.

Luckily, I have the monstrous Palstar HF-AUTO to take care of such things.  Even then, there is no 'free lunch'; beyond about 5:1 SWR you can be sure something will flash over sooner or later; in my case usually the N connector between the balun and feed line.

The dream of a multi band antenna is mostly that when it comes to QRO - a dream.  Possibly the closest solution is a fan dipole or a cobwebb antenna.

Perhaps its time to tune up that G5RV so it meets specifications, or upgrade antennas?

As for the endfed, throw that thing away mate.  No point pumping QRO into an antenna when you have no idea what the radiation pattern actually looks like.  The only multi band antennas that have desirable patterns across all bands of usage are the fan dipole, cobwebb and multi band Yagis (trapped or nested).  There may be a few others, but a high impedance random wire "half wave" isn't one of them.
« Last Edit: March 19, 2018, 10:56:15 PM by VK3BL » Logged

J.D. Mitchell BA  - VK3BL / XU7AGA - https://www.youtube.com/ratemyradio - Honesty & Integrity
AC2RY
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Posts: 761




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« Reply #3 on: March 20, 2018, 08:01:33 AM »

The built in ATU is only designed to match ~3:1 mismatches; the same as most transceivers.

Its really just designed for 'trimming up' mono band antenna such as a Yagi on band edges.

If your radios won't match the antennas, and the amp won't either, the simplest explanation is the antennas are presenting a higher mismatch.

My G5RV, which admittedly I never 'tuned' for my specific installation - I just slapped it up there - is nowhere near the theoretical specs published online.

Luckily, I have the monstrous Palstar HF-AUTO to take care of such things.  Even then, there is no 'free lunch'; beyond about 5:1 SWR you can be sure something will flash over sooner or later; in my case usually the N connector between the balun and feed line.

The dream of a multi band antenna is mostly that when it comes to QRO - a dream.  Possibly the closest solution is a fan dipole or a cobwebb antenna.

Perhaps its time to tune up that G5RV so it meets specifications, or upgrade antennas?

As for the endfed, throw that thing away mate.  No point pumping QRO into an antenna when you have no idea what the radiation pattern actually looks like.  The only multi band antennas that have desirable patterns across all bands of usage are the fan dipole, cobwebb and multi band Yagis (trapped or nested).  There may be a few others, but a high impedance random wire "half wave" isn't one of them.


G5RV and its cousin ZD6BKW can be used on many bands with wide-band tuner at feedpoint. But I would not try to push more than 1kW into it on any bands.  Though if you look at REAL 1kW rated wide-band tuners ( here http://www.barrettcommunications.com.au/1kw-atu/ is an example), you will understand why.

« Last Edit: March 20, 2018, 08:04:01 AM by AC2RY » Logged
K6BRN
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Posts: 1348




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« Reply #4 on: March 20, 2018, 08:54:24 AM »

Lloyd (KD2JVX/K2JVX):

The SPE 1.5K-FA is a pretty potent amp and I'd be very careful driving a lot of power into the wire antennas you've mentioned and on your web page.  In the case of the MyAntennas EFHW-8010, it is rated at 1.5KW ICAS (low duty cycle).  I upgraded to the 2K version because I run RTTY and the high duty cycle of this mode will overheat the 49:1 matching transformer in the lower power models.  Even with the 2K version, I have to watch SWR carefully and never run more than 500W in this mode.  SSB is considerably lower duty cycle normally, but with liberal application of compression can approach 50% as well.  So I'd advise you to be careful.  Note that I have and use (very successfully), several EFHF-8010, EFHF-4010 and an EFHW-16040 with good results, on the road and at two QTHs.  Power is the Achillies Heel of EFHW antennas, and Danny's are the highest power examples I know.  He is continually improving their design to increase power handling (latest units include venting), but power application must still be watched carefully when approching the legal limit.

With regard to SWR approaching 3:1 on the EFHW-8010 on 80M, two causes I know of can result in this effect:  1.  Coupling to nearby structures that detune the antenna, and 2.  Heat damage to the toroidal cores in the matching transformer.

If you've used the EFHW-8010 on the road (in particular), You've probably noticed that it is sensitive to height above ground and nearby power lines and metallic structures - more so on 80M than any other band.  This is due to the long wavelength enhancing capacitive/inductive coupling to objects in the "Near Field".  Structures or ground will have a significant effect if they are within about 130 feet and a pronounced effect on SWR if they are within 60 feet.  This comment is NOT from armchair theory - it is my from installation and use of several of these antennas on the road, at my QTHs and at other hams QTHs.  In some cases we've had to trim or lengthen the wire to adjust the resonant frequency, particularly at one location that is surrounded by power lines.  Unfortunately, this tends to de-tune the other bands.  Pretty much par for the course for any 80M antenna without enough clearance to nearby conductive objects.

One other note... I've noticed that on 80M in particular, if the antenna is affected by nearby objects, the SWR may vary with power level.  So it may be higher (or lower) at 100W than 500W.  I do not have an explanation for this other than it seems to happen.

Also... many trap antennas (Yagi, vertical, dipoles) and those with matching transformers (like the EFHW and others) cannot sustain more than 500W CW, including Cushcraft, HyGain and Mosley models.  Look at the specs before you buy one and drive the SPE 1.5K-FA into it at full power.

Congrats on taking delivery of a very nice amp!  But note that you'll have to be more careful of feedline, antanna and matching network capacity to fully exploit it's capabilities.

Brian - K6BRN

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KD2JVX
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Posts: 2




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« Reply #5 on: March 20, 2018, 11:00:49 AM »

Thanks  all, and particularly to Brian - K6BRN.  It is clearly a whole new ball game.  Somewhat frustrating as it is completely automatic with no bypass or manual overrides except to change power or by pass the amp completely.  That said the CAT control works, as if they tested my particular radios.   So it was automatic as advertised.   Except that when I push the tuning button on the 7300 i hear servos working in the 7300, which should not be the case as pushing that button in cat control should activate the tuning sequence in the amp itself as it did with my MFJ-939 (now disconnected).

Any ideas as to the "best" location for a choke? 
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AC2RY
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Posts: 761




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« Reply #6 on: March 20, 2018, 12:46:10 PM »

Thanks  all, and particularly to Brian - K6BRN.  It is clearly a whole new ball game.  Somewhat frustrating as it is completely automatic with no bypass or manual overrides except to change power or by pass the amp completely.  That said the CAT control works, as if they tested my particular radios.   So it was automatic as advertised.   Except that when I push the tuning button on the 7300 i hear servos working in the 7300, which should not be the case as pushing that button in cat control should activate the tuning sequence in the amp itself as it did with my MFJ-939 (now disconnected).

Any ideas as to the "best" location for a choke? 

When you load transceiver to amplifier, you need either disable tuner in it or configure it to use "external tuner", which also means that you need connect device that serves like tuner to "tuner" port in your ICOM.
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VK3BL
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« Reply #7 on: March 20, 2018, 06:30:57 PM »

G5RV and its cousin ZD6BKW can be used on many bands with wide-band tuner at feedpoint. But I would not try to push more than 1kW into it on any bands.  Though if you look at REAL 1kW rated wide-band tuners ( here http://www.barrettcommunications.com.au/1kw-atu/ is an example), you will understand why.

I can tune my G5RV up with the Palstar HF-Auto on every band, that said, I can only push decent power into it on 80, 40 & 20.

The tuner isn't the problem - the feed system is.  As the SWR increases so does the voltages present, and thus the demand on the feed line.  In winter, even on 80M there is often enough moisture about for the feed line to arc over at 'dry' power levels.  Severely non resonant bands I can usually manage 250-400 Watts, but I don't like the strain it places on my equipment, and the results DX wise are never that impressive anyway.

The moral of the story is that pushing high power into anything above a 5:1 SWR is quite the engineering challenge; to the point that one cannot use traditional HF connectors like the "UHF" Connector and the N Connector.  You're best off having no connectors in line, or using say the 7/16 DIN series.

Of course, you could just chose to use resonant antennas on the low bands (or feed point matched antennas with sizeable matching components), and something like a Heavy Duty Cobwebb for 20-10 or a HD Yagi.

"All Band" antennas are much like the tooth fairy and Santa Claus.  Once you graduate to real power you realise they're the stuff of fiction.

Just look at the size of the unbalanced output on that Barrett tuner referenced; at a guess I'd say its rated somewhere between 7500v & 10,000v, which should give you some idea of the voltages encountered when feeding non resonant antennas with QRO.

I can't speak for everyone, but I tend to keep an 'all band' antenna about 'just in case' for low power work, and erect dedicated and known pattern antennas for QRO work.  My strategy is to implement QRO antennas for my favourite bands, and/or the bands I am chasing DXCC on.

At the moment thats 80M, and I'm more than half way there Smiley. Once that endeavour has been reached (and the solar cycle gets better), I'll go after 15M & 10M and some of the WARC bands.

73, Jarrad

PS.  Don't damage your amp by pushing too much power into an antenna that you know will ultimately fail.
« Last Edit: March 20, 2018, 06:33:45 PM by VK3BL » Logged

J.D. Mitchell BA  - VK3BL / XU7AGA - https://www.youtube.com/ratemyradio - Honesty & Integrity
K6BRN
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Posts: 1348




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« Reply #8 on: March 20, 2018, 11:12:45 PM »

Lloyd (KD2JVX/K2JVX):

To answer your question:

Quote
Any ideas as to the "best" location for a choke?

To reduce stray RF in the "shack" that originates from RF on the outside of the coax feed line, often due to a mismatched antenna, a reasonable place to put the choke is on a 5 foot or so jumper from your amplifier, with the other end connected to the N feet of coax going to your antenna.

But there are also other ways to do this that include a choke on a jumper a few feet from the antenna and a coax shield grounding block/lightning arrestor on a ground rod just before the coax enters your home/"shack".  This approach tends to limit stray RF better and works well with many antennas, such as rotatable dipoles and Yagis, but interferes with the ability of some antenna types (mostly wire antennas) to use the outer coax shield as part of the antenna system - the so-called "counterpoise".

Try a simple feed line choke at the shack end first, focus on resonant antennas and limit power to the antenna to what it can handle and see what happens.  If you still have RF in the shack, you may consider the alternate scheme outlined above, or consider where you've routed your antenna relative to your radio equipment and house wiring.  One ham I helped had his wire antenna running just about 12 feet above his radio equipment and very close to his roofline.  Whenever he transmitted substantial power on 40M his garage door would begin opening and closing and he'd have stray RF problems in his "shack", which was in the garage.  A simple feed line choke was not going to solve the problem because both his shack and house wiring were too close to the antenna wire, and the RF was coupling into them very strongly via inductive and capacitive (near, near) near field effects.  We changed the antenna route to move it much further away from the house (back yard with minimal house overlap) and the problem went away.

Myantennas (and many others) sell well built, ready made feed line chokes.  The CMC-130S-3K might be a good choice for you - see this link.

https://myantennas.com/wp/product/cmc-130s-3k/

Best Regards,

Brian - K6BRN
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