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Author Topic: WHICH MOBILE AMP ?  (Read 647 times)
N4GRN
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Posts: 47




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« on: May 08, 2003, 06:39:43 PM »

I am desiring to add an amp to my mobile rig. I spend about 80% of my life in the car so much of my HAM time is in the car.

I know the arquments against an amp in the car as I posted here once before about an amp for the car. I agree that 100W is usually fine, but with large pile-ups and at time due to location a little more power would be nice. I have logged over 38 countries since getting my license back in February 2003 all from car with 100W but simply lost many due to large pileups and not enough power.

I am running a 706MKIIG, a HiQ antenna (4"coil/6-80M), and the AmCom ASAC antenna controller.

I am aware of all of the power issues with batteries and etc but those issue is resolved by new alternator, extra batter at amp location, 2/0 wire and etc.

I am also aware of all of the bonding. I have gone to the extreme with bonding every conceivable part of the body and frame.

I am looking at the Skywalker 1000W amp. I will be using it at my 2nd QTH in Nova Scotia so I can buy it there for my use there assembled by maker.

I am told that without filters the only issues are that some SWR meters will read the harmonics that are rejected by the antenna and give false readings.

Other than that I am told that there is no need to have the alternate filters added as they will simply make me have to stop and change settings when I change bands and while driving that is an issue.

Also, if I place the ASAC after the amp and tune with amp off using the 706's auto tune button (as it works with the ASAC) will I have issues of harmonics causing the 706 to cut power back due to the harmonics once the amp is on?

I also thought about adding the R.F.APPLICATIONS P-3000 DIGITAL WATT METER with auto shut down on high SWR. Will I have problems with this unit and harmonics?

I am new to this so I need help from those that have experience.

Maybe another amp is recommended, maybe other issues that I am not aware of, so let me know.

73 N4GRN

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K0BG
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« Reply #1 on: May 09, 2003, 09:44:21 AM »

I wouldn't touch that amp if it was given to me! And if you buy it, you're asking for trouble.

The little Ameritron by MFJ can be had for $700 or so, and the SGC at about $1,100 with the fan accessory. Both are type accepted. If you keep them cool, they'll give years of service.

Alan, KØBG
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K5LXP
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« Reply #2 on: May 09, 2003, 01:30:43 PM »

An amplifier that generates harmonics strong enough to be measured as reflected energy on a passive SWR meter?  So much for -40dBc...

Mark K5LXP
Albuquerque, NM
k5lxp@arrl.net
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WB2WIK
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« Reply #3 on: May 09, 2003, 01:51:27 PM »

I ditto Alan's remarks.  Why intentionally buy and use an amplifier that knowingly violates the Part 97 spectral purity limits, especially when there are far better alternatives?

The Ameritron and SGC are excellent, current, and FCC accepted products (the SGC bandswitches automatically) and the Metron kW mobile amp, while no longer manufactured, are very available on the used market and also meet Part 97 purity limits.

I doubt you'll be able to use the tuner when running high power.  Most active HF mobileers who run high power stick with one or two bands and optimize their antennas for those one or two bands, so no tuner is required; or of course, a high-power well-deployed screwdriver antenna can handle the power and needs no tuner.

WB2WIK/6
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N4GRN
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« Reply #4 on: May 09, 2003, 04:59:05 PM »

Thanks for the comments. I quess I will keep looking for the Metron or but an SGC.

I need to clarify a few things that you all apparently mis-understood.

1) In my post I said this amp would be used in CANADA NOT USA. I have a home there and leave a car there.

Since several hams there (they mentioned the harmonic issue was the only problem they had) are using the amp I assumed it was approved there as the manufacturer says that there are no problems shipping to anywhere but USA due to the emissions issues.

I assume from your comments that it is not suitable for use anywhere and is junk. That answered my question as to was it an OK amp.

2) One of my questions was in regard to the harmonics causing issues with the 706 assuming the antenna was resonate. I did not get an answer to this question.

3) I assume that some of you do not realize that the "HiQ Stealth antenna" is a "screwdriver" antenna.

I assume that is why you took my word "controller" and changed it to "tuner". I know that a tuner is not needed with a screwdriver. All that is needed is maybe a shunt coil or unun to help load on 80M and a switch to move the coil contacts up/down to resonance.

The "ASAC" by AmCom is basically a "computer controlled up/down switch" and not a "tuner/transmatch" etc. It can handle 1000W but is doing no matching.

I appreciate the point blank facts that this amp is no good. I knew that it was not accepted here in US but did not know it was simply a piece of junk.

73   N4GRN

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K0BG
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« Reply #5 on: May 09, 2003, 06:50:44 PM »

George, let me explain this to you as best I can.

Both Steve and I told you, in essance, the amp is NOT approved by the FCC. And...it is NOT approved for use in Canada either! It is basically junk, it is poorly made, and the maker has ignored the FCC's warning about making them available without certification. In other words, if you buy one, you are own your own as to any rules violation you make. Nuf said about the amp!

I don't care if you call it an auto-tuner, tuner, or adjuster, the result it the same. It moves the coil up or down with in the screwdriver tube to resonant the antenna on the band in question, so it really doesn't matter how the tuning is done. Nuf said!

The problems the amp may or may not present to the 706 is surely not a transmit problem unless the input Z isn't near 50 ohms non-reactive. Nor is it on receive unless the amp's transfer relay or preamp (if it has one) isn't up to snuff.

What Steve said about high power mobile is dead on. For the most part, it isn't worth the extra S unit (or may be an S unit and a half) unless you have a poor antenna to start with. The Hi-Q is one of the better screwdrivers around, but it will not handle a true 1,000 watts. Maybe 400 to 500 out of the typical mobile amp, but that is all.

It is best to optimize the other factors first. Steve has gone on record many many times about maximizing your antenna system first before adding insult with an amp. Please don't misunderstand me, I am not aginst high power mobile (I've been there and done that even with 1,500 watts out!), but these days I have just as good a signal without it by taking Steve's advise. You should too.

Alan, KØBG
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N4GRN
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« Reply #6 on: May 10, 2003, 02:06:44 AM »

Alan and Steve:

I WAS NOT QUESTIONING YOUR COMMENTS IN MY LAST POST.

I have taken your advice on several other occasions and have been very happy with the results. In specific Alan's emails regarding UNUNs, fed point height, bonding, etc.

I am having a ball here in Atlanta with 100W and have no intention of using an amp here. I have contacted Russia, Germany, France, England, Scotland, Ireland, Uganda, Africa, Slovenia, Ukrane, Israel, Saudi, etc all with good signal reports and some with large pile-ups. I have worked several callsigns on 10, 15, 17, and 20 from the car in the same day.

Following your prior suggestions convinced me that proper antenna set up makes the difference.

I was considered that amp only for Canada and was falsely told by the maker and some local Canada HAMS that it was very good and approved there. I was in doubt and thus my original post. SGC was my original choice and that is what I will probably go with.

I WAS NOT QUESTION YOUR COMMENTS. I APPARENTLY MIS-STATED MY SECOND POST AS I WAS AGREEING WITH YOU AND ONLY ASKED FOR AN EXPLANATION FOR GENERAL KNOWLEDGE ABOUT THE HARMONICS AND THE 706.

As for the tuner comment I made. Again I was not questioning your comments. I thought that your comment  "a tuner is not needed with a screwdriver" meant that you thought that I was actually unsing a tuner like the SGC or etc., to match the antenna to the transceiver. I was explaining that it was a position controller for the coil. I was not arguing the statement of yours.

I appreciate your advice and speedy answers. I just wanted that extra punch in Canada as that will be my only station there for a while as I am remodeling my house. Looks like my original choice of the SGC is what I will be doing.

73  N4GRN
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« Reply #7 on: May 11, 2003, 02:07:15 PM »

Mobile amps are generally poorly designed  except for the Metron.  I have seen Ameritron and other manufactured amps that blow up with any antenna problem you might encounter.  Most transistor amps are operating at their max or over power limit.  If the swr should rise very high because of an antenna fault, you may have a $300 repair bill real fast.  The protection circuits don't always work.

I have built 2 1.2kw 28volt amps using MRF422's.  One thing I learned is that transistor amps work much better at reduced output by running lower voltage.  20 volts on MRF422 makes the amps almost industructable.  Running a 12volt amp at about 9 volts will do the same. Getting 300 watts from an Ameritron at reduced voltage will get you a longer lasting amp.  Also, if you examine the rocks and design of the Ameritron, its really a 300 - 400 watt amp.  Ameritron is really pushing that amp by saying its a 500 watt amp.
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WB2WIK
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« Reply #8 on: May 12, 2003, 02:54:22 PM »

N4GRN, I'm sure you know it's human nature to like whatever we each individually own.  I'm a little bit different, personally, in that when it comes to equipment of any type I have no loyalties and always figure that "everything stinks" until proven otherwise, hi hi.

My experience with the Metron 1000 (in the past, years ago, since it is no longer made) as well as the Ameritron ALS600 and the SGC Power Cube is all quite good.  I've used these three FCC-accepted products, never had one fail, and really never had any problems with them at all.  A really long time ago, I even had a Heath "Mobile KW" amplifier, which used a pair of 572B tubes (!) and could nearly suck the life out of an average car battery and alternator system within about fifteen minutes, but it worked quite well and never failed.

The lower-cost "CB" type amps (no bandswitch!), however, have been the subject of many complaints.  There must be some reason that I see these at the local equipment swap meets selling for practically nothing (because they've blown up and are no longer working) every single month.  Possibly CBers using them abused them to death, or just as likely they weren't very good products to begin with.

I doubt that "harmonics" alone would cause any significant change in an SWR reading....those harmonics would need to be awfully strong for that to occur.  Although we are supposed to adhere to -40dBc (harmonics 40 dB below desired frequency carrier power), a really *bad* amplifier might be -20dBc (which is very poor), but that would mean a harmonic that's 20 dB below the fundamental, or 1/100th the power of the fundamental...that's only 1%.  A 1% change in reflected power due to antenna mismatch is not something that can be read by an SWR bridge.

WB2WIK/6
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N4GRN
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« Reply #9 on: May 12, 2003, 06:25:02 PM »

WB2WIK
Thanks for the comments.

I am also skeptical until I see it for myself. Money is a factor but doing it right one time makes more sense than half doing it many times. Thus my looking at as many options as are available for the amp.

My gut feeling was the SGC Amp in the start. Then I was told that it would power down while driving due to fluctuations in the swr due to road conditions, etc. Then I heard that some of the "CB types" were more powerful and more durable and work just as well. Then I'm told I do not need an amp at all.

I am going to order an SGC this week. It looks like the most quality for the buck.

I have a feeling that what the hams running amps that are the cb type were describing is what I found upon first installing and using my 706 with the ASAC controller. I had to place ferrites on everything before I could get the ASAC and 706 working to achieve the lowest swr. It was simply RFI issue in general. More bonding and ferrites solved that problem.

I'm a new HAM but I'm an old experimenter with many things so I'm not stupid just asking for opinions to verify my gut feelings.

THANKS and 73 N4GRN
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G4ZOW
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Posts: 41




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« Reply #10 on: May 25, 2003, 04:59:07 PM »

Just my 2c I mean 2p.

Mention was made of the Skywalker and it's poor harmonic filtering.

Among my collection of mobile HF amplifiers is a home brewed 8 device Skywalker amp. I purchased the complete kit which does include a simple manually switchable low-pass filter network. After final tweaking of each filter my engineer colleague measured a minimum of just under -40dB down. I seem to recollect that the filter design was taken strait out of the ARRL handbook, but I could be wrong. The fact that these filters are not relay switched as in the SGC (optional manual or auto switching in the Henry, Metron and Tokyo Hi-Power) is irrelevant.

I was under the impression that in the US one could 'homebrew' an amplifier for one's own use (IE not for commercial gain) and that you did not require an FCC approval ID. Tell me if I'm wrong here guys. Us Brits know nothing.

I wholeheartedly agree re Screwdrivers and the fact is I've yet to find one that does not suffer from meltdown at a true, Bird 43 Kw in the mobile. I sent two BB3's back years ago and have not been back to Screwdrivers since though there are one or two other designs I'd like to try. On 160 and 80m I have no problem in suffering from inter-turn arcing and corono discharge from the corona ball atop the BugCatcher at the 500w level.

I have spent a lot of time, and money on the charging system and can pull 150A CW keydown with only .3v drop across the battery. I hold 14.3v across any amp terminals without any problem.

I am looking into a DC-DC converter to generate 48v to run a bunch of FET's. I'd dearly like to be the first to see 1500w peak output from a 12v charging system just for the sheer technical challenge however I have no design experience playing with magnetics.

(((73)))

Phil G4ZOW
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