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Author Topic: Which amp to start with?  (Read 46572 times)
KB1SNJ
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Posts: 139




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« Reply #150 on: January 30, 2017, 09:52:57 PM »

thanks a million guys, glenn for the diagram and calc on the coil. I will get 10 more feet and a couple and add that on. jarrad thanks for the explanation of the 160 match with no choke.

by working with this piece of wire I am starting to get the fundamentals just a bit.

I will try to add a couple more radials (really can only go in one more direction), and later apply the diagram and longer coil etc. and another choke. the monitor distortion is a good "tool" for seeing RF in the room. I suppose that could also be from the radiating element itself. not sure how to tell the difference just yet.

it seems that 50ft of wire straight up should be able to do something when little screwdriver antennas work for people down to 80M

I also found a youtube vid that steps through using EZNEC, so now I can try to get used to that!

btw I stumbled onto this talks about using smaller verticals on 80/160. key takeaway is use radial system and expect low net ERP. (Although 5% of 600W is 30W)

http://www.eham.net/ehamforum/smf/index.php?topic=81071.0;wap2



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VK3BL
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« Reply #151 on: January 31, 2017, 06:08:10 AM »


it seems that 50ft of wire straight up should be able to do something when little screwdriver antennas work for people down to 80M

btw I stumbled onto this talks about using smaller verticals on 80/160. key takeaway is use radial system and expect low net ERP. (Although 5% of 600W is 30W)


Thanks for the kind words Chris.  Its been an enjoyable thread, and I think you're doing a great job learning about things.

The only thing I will add is that it isn't necessarily as simple as just settling for a low ERP, especially if you wish to use an amplifier one day.  The thing you have to understand, is that if you're only radiating say 5% of the power, that means the other 95% is being lost somewhere.

Now, at 100 watts, losing 95% of it in a little screwdriver probably isn't a huge deal, especially in SSB / PEP modes.  However, if you were to run 1000 Watts input into the system, suddenly it has to deal with 950 watts of essentially heat; thats going to demand some serious sized components.

50ft is a nice sized radiator, don't get me wrong, but on 160M, its about 1/10th of a wavelength; well and truly on the electrically short side.

I'm not trying to discourage you - its definitely doable, just don't underestimate the power handling required of the matching components. 

It sounds like you're on the right track with the 1/4 inch copper.  Most of the loss will be in the coil, and 1/4 inch should handle it just fine.
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J.D. Mitchell BA  - VK3BL / XU7AGA - https://www.youtube.com/ratemyradio - Honesty & Integrity
W9IQ
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Posts: 3397




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« Reply #152 on: January 31, 2017, 06:18:18 AM »

I would view the losses on 160 meters coming primarily from ground losses due to an inadequate radial system.

- Glenn W9IQ
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- Glenn W9IQ

I never make a mistake. I thought I did once but I was wrong.
KB1SNJ
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Posts: 139




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« Reply #153 on: January 31, 2017, 12:13:08 PM »

hi glenn what does that mean?  lets say 900 watts being "lost" and under your post thats "ground losses" what does that really mean, that electrical energy is going down into my ground rod, and the 3 radials? or a percentage thereof, with the rest converted to heat in the "loading coil" (if thats what the copper coil is properly called)?

by the way just to keep this on track, 160m is not a priority here at all. not looking to do much radio with it but making that coil and capacitor setup etc, and discussing it is the real benefit as the principles apply to any situation of running an antenna electrically shorter than the 1/2 wavelength (I think). it seems from this recent posts that if the wire is 1/10 wavelength, then building a loading coil creates a nonradiating section that absorbs (and converts to heat) the radio frequency rather than just reject it back the other way?  but then there's the ground losses aspect which glenn mentioned.

which then (sorry) makes me wonder if there was no ground or radials at all, just the wire and loading coil, what happens to the radio energy situation then?



I would view the losses on 160 meters coming primarily from ground losses due to an inadequate radial system.

- Glenn W9IQ
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W9IQ
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« Reply #154 on: January 31, 2017, 01:11:42 PM »

Chris,

The earth under our feet is really a poor conductor of RF energy. For a vertical antenna this means that if there is not a sufficient ground plane or counterpoise that a part of your RF transmit power is heating the earth as it tries to find a return path. This also means that the RF energy will search out other lower reactance paths. In your case it has found the shield on the outside of your coax to be one of those paths so as a result, you have common mode current. The balun that you built puts a high reactance (specifically high resistance) into the outer shield to discourage this as a return path.

There will also be other losses due to the resistance of the antenna components, the inefficiencies of your unun, etc. Some of these will become much more apparent if you apply high power to your antenna. Things that have sufficient resistance will melt and things that cannot handle the higher voltage will arc. This is why several respondents, including me, on this thread have recommended getting everything cleaned up first before you consider going QRO as this will tax everything in your antenna system.

Specific to the 160 meter coil, in itself it will not represent any significant percent of loss of the overall antenna system. But consider that your radials will become even more inadequate at those lower frequencies so the effects mentioned earlier could become worse.

- Glenn W9IQ

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- Glenn W9IQ

I never make a mistake. I thought I did once but I was wrong.
N1ZPY
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Posts: 38




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« Reply #155 on: February 02, 2017, 03:48:38 PM »

If you don't mind going out to the base of the ant to change bands some ideas from this ant might help. .http://www.arrl.org/files/file/Technology/tis/info/pdf/7806016.pdf
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KM1H
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Posts: 5281




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« Reply #156 on: February 03, 2017, 08:21:01 AM »

Chris, you have received a wide range of ideas, from excellent to useless.

Here are a few of mine that are far from unique but well proven.

Single 3-500Z Amp:

Ameritron AL-80A or 80B. The original 80 is OK if it was factory updated.

Heathkit SB-1000, needs a few simple mods for 160 and WARC bands and is an almost clone of the AL-80A; Ameritron supplied most of the parts.

Amp Supply LK-450 Rugged and reliable

Several other single 3-500Z amps that were relatively low production but do show up at times. Im another who has no use for the AL-811 series until the friggin' Chinese stop shipping garbage.

Any amp that is 20-25 years and older should have the PS filter caps replaced and their are complete replacement board and parts kits available for many.

Several other vintage amps are fine but you should be aware that PM, repairs, and mods are often required. I use an old Dentron Clipperton L and DTR-2000L strictly as AM linears on a separate bench devoted to vintage "hollow state" gear from the 30's to 60's.

Carl
KM1H
Ham since 1955


RFI

Read and digest the info in these links, there is nothing better available and used by the serious hams who will not tolerate RFI while in a contest DXing, and otherwise dont want to be bothered by family or neighbors when on the air.

http://audiosystemsgroup.com/RFI-Ham.pdf    The latest update from K9YC

http://www.audiosystemsgroup.com/K9YC/K9YC-old.htm  Hours of good reading

Even the best of common mode suppression does not fully eliminate what radiates directly from electronics in your home and neighborhood. Snap On ferrites are by far the least effective and cost the most. I had to spend a lot more for ferrites on all sorts of power cords around the house as well as toss all the small switching PS wall warts and go back to old fashion linear versions. My Comcast modem and TV box plus a few larger switching supplies were the hardest and required being wrapped in aluminum foil where it wasnt blocking ventilation plus ferrite. A portable AM radio is best for noise hunting as is shutting off all but one circuit at a time at the main panel. Or shut all off and what remains is not from you but do all the feedline work first.



Baluns and ferrite cores:

Most of what is on the market is overpriced, junk or both. Especially stay away from Amidon and Palomar along with the big color ads in the rags which cost a lot of $$ to run and you are paying that premium. This is one area when homebrew is usually the best.

The 52 mix is 3X the price of 43 and offers very very little extra except on paper.

I always shop Mouser first and their Fair-Rite 2643803802 and 2631803802 are the best choices. If you really need the best at 160 use the 31 mix and you can also stack one or more of each mix for full 160-10M coverage. Most of my antennas are monoband or HB 2-3 band verticals so I use 31 for 80/160 and 43 for 30-6M.



Power Rating:
I would never use RG-58, 59, 6 or equivalent at even 600W since the voltages and currents may be excessive on chokes AND baluns and you wont know unless you try them. Any of the similar size Teflon coax is far superior in that application even if it does require an adaptor to go to the regular RG-213 or LMR-400 (or equivalent) feedline.
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KB1SNJ
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Posts: 139




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« Reply #157 on: February 05, 2017, 10:53:16 AM »

OK a few dumb questions, as I make my way through the reading and resources above:

1) how to design (build) a 1.5 or 2kw (robust) unun thats 9:1
2) will a remote tuner unit do better job keeping the RF at the antenna and not coming back into feedline than inside tuner, or is that all a function of the chokes?
3) if I were to hoist an inverted vee by using 100ft of wire instead of 50 and bringing the other leg down say 35ft away, would that radiate better than a single wire, and what kind of impedence would be seen at feedpoint? (the broadside if applicable would face WSW which would be very good from New England)



While I make my way through the resources posted above (thank you!), I have a couple basic questions:

I now understand what the ratio is in my 9:1 UNUN, it reduces impedance by a factor of 9:1. So my wire must present an impedance of around 9 times 50 or 450 more or less depending on length and maybe other factors.

My question is that if I wanted to build a heavier duty (for more power) 9:1, how can I scale that up? I do know that Balun Designs sells a 2kw 9:1 but I'm going to guess that ferrite size and formula and also the gauge and number of wraps of the three wires affects the final results. I wonder how to measure a unun anyway? The post a few posts back told me to put a 450OHM resistor on the antenna size and check the coax input side ahhhhh that must be how to do it. So resistance is resistance whether it's a straight 50ft wire against ground or shunted through a resistor on the antenna side of the unun?
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AC6CV
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Posts: 302




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« Reply #158 on: February 05, 2017, 01:44:06 PM »

If it were my shack I would first make sure my present antenna was properly matched and no RF in my shack or in nearby equipment. Then possibly think about an amp. I don't have any problems with working nets on 75 in my RV with my home brew  23 ft vertical and loading coil. However, it is properly matched and the load is resistive.
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K6AER
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« Reply #159 on: February 05, 2017, 01:54:34 PM »

A 9:1 Balun, that will handle the RF voltage of 1.5 KW, will have to with stand 2500 volts on the output not to mention the heating of the toroids.  This assumes the antenna is somewhat resonate at that output impedance. This is a recipe for disaster. You need a more resonate antenna for the low bands when running power.  Not all locations will accommodate 160-80 meter operation. Most hams have multiple antennas to cover most of the bands. I addition you have never mentioned what local noise sources are in the area. Having a working antennas on the lower band will be a moot point if your noise floor is a non-workable level.

I noticed that we are up to almost 160 posting on this subject, 41 from yourself going back three weeks. I suggest you do some reading with the ARRL Antenna Handbook. It is not fair to ask the ham community to spoon feed you with knowledge when you have not taken the time to understand the basics. 
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N1ZPY
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Posts: 38




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« Reply #160 on: February 05, 2017, 02:29:47 PM »

I would also suggest buying or borrowing an antenna analyser to help you with your antenna.  As many others have said you need to fix it before you add an amp. 
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AC2RY
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« Reply #161 on: February 05, 2017, 06:32:45 PM »

I would also suggest buying or borrowing an antenna analyser to help you with your antenna.  As many others have said you need to fix it before you add an amp. 

He has a good one already. The problem is he does not fully understand how to use it. This is time for CHRISDX to seat and read BOOKS, not posts on forums.
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W9IQ
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« Reply #162 on: February 05, 2017, 06:34:18 PM »

Chris,

A few thoughts on your questions.

You should determine if you even need the 9:1 unun. Take your antennalyzer out to the base of your antenna. Take and record measurements from all of the bands from which you intend to operate, with and without the balun.

The purpose of putting the tuner at the base of the antenna is to reduce the extra loss in the coax due to high SWR. It will do little to nothing in the way of reducing stray RF in your shack.

The inverted V is a good idea. It is a balanced antenna so this in itself should reduce the RF coming into your shack via the coax shield. Do install your homemade choking balun at the apex of the V. Do not guess at a length for the legs of the V - look it up or model it for the primary bands on which you wish to operate. The primary direction of a V antenna is out the opening of the V when the antenna is 1/2 wavelength long.

- Glenn W9IQ
« Last Edit: February 05, 2017, 06:47:53 PM by W9IQ » Logged

- Glenn W9IQ

I never make a mistake. I thought I did once but I was wrong.
WW8X
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Posts: 34




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« Reply #163 on: February 07, 2017, 11:41:50 AM »

Your lot sounds like mine. Very small city lot with virtually no room for a decent antenna. On my 2-story house, I roof-mounted a Hygain 5BTV vertical trap antenna using a tripod mount and two radials for each band spread across the roof shingles fastened with some clips to the shingles. I put a 6" x 10 turn coil in the coax at the feed point. I live in a valley of sorts, with hills on 3 sides – yet, on all 5 bands (10, 15, 20, 40 and 80) I can usually work any station I can hear with often surprisingly great signal reports. I use a Drake MN-2000 tuner and have had no RFI problems since day one. As others have said: you shouldn't consider an amp until you get your antenna and RFI issues solved.
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VK3BL
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« Reply #164 on: February 07, 2017, 04:03:40 PM »

The inverted V is a good idea. It is a balanced antenna so this in itself should reduce the RF coming into your shack via the coax shield. Do install your homemade choking balun at the apex of the V. Do not guess at a length for the legs of the V - look it up or model it for the primary bands on which you wish to operate. The primary direction of a V antenna is out the opening of the V when the antenna is 1/2 wavelength long.

- Glenn W9IQ

Another thing I would add to Glenn's advice is do not be concerned about antenna pattern just yet. 

Whilst its 'sexy' to talk about patterns, and several manufacturers tout verticals as a solution, you have to be mindful of the overall Effective Radiated Power of any given antenna.

Eg, there is no point gaining 1dB at a lower take off angle using a vertical, if its Effective Radiated Power is 3dB down over a dipole.

With my own suburban block, I have never been able to install a vertical that has managed to outperform a dipole for DX.  99% of the time, the Inverted-V dipole is just as good with DX, but much, much stronger for local rag chews.

Its fun to play around with EZNEC etc, but the most important thing you should be paying attention to in your (our) situation is how easily the antenna can be fed on the bands we wish to use.

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