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Author Topic: Which amp to start with?  (Read 46841 times)
KB1SNJ
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Posts: 139




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« Reply #30 on: January 15, 2017, 02:25:25 PM »

Thanks Glenn, very big help. Im starting to get it. Looked at this page regarding choke at feedpoint.

http://palomar-engineers.com/antenna-products/1-1-balun-kits/choosing-a-feedline-choke

 I'd appreciate suggestion on the very best broadband feedpoint chokes available ready to go that I can procure.

After that then I can experiment with some homebrew ideas and have something to compare to.

Hopefully in my case one choke will mitigate the RF common mode coming back although that site did describe situations where they need to be added at intervals (Im imagining with long feedlines).
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NI0C
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« Reply #31 on: January 15, 2017, 03:38:20 PM »

Here's what I use: http://www.balundesigns.com/feedline-isolation-baluns/

I like that Balun Designs publishes graphs of choking impedance versus frequency, so you know what performance you are getting.
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KB1SNJ
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« Reply #32 on: January 15, 2017, 05:07:20 PM »

Cool thanks. Which model? Single or dial core, 1-31 or 1.5 to 54?

Im going to assume 1.5 to 54 to cover 6m, dual core.


Quote from: NI0C li :)nk=topic=113083.msg974213#msg974213 date=1484523500
Here's what I use: http://www.balundesigns.com/feedline-isolation-baluns/

I like that Balun Designs publishes graphs of choking impedance versus frequency, so you know what performance you are getting.
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VK3BL
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« Reply #33 on: January 15, 2017, 05:27:55 PM »

Cool thanks. Which model? Single or dial core, 1-31 or 1.5 to 54?

Im going to assume 1.5 to 54 to cover 6m, dual core.


Quote from: NI0C li :)nk=topic=113083.msg974213#msg974213 date=1484523500
Here's what I use: http://www.balundesigns.com/feedline-isolation-baluns/

I like that Balun Designs publishes graphs of choking impedance versus frequency, so you know what performance you are getting.

With your current setup already in place Chris, my suggestion would be to purchase a FT240-43 core, and wrap your coax round it as many times as you can.

Steve G3TXQ has published the design graphs, you can see them here:
http://www.karinya.net/g3txq/chokes/

I have used both his 12 Turns on FT240-43 & 11 Turns on 2x FT240-52.  Both provide excellent common mode blocking performance as advertised.

Given that you can pick up a FT240-43 core for ~$10 USD, and just pass your coax through it a few times, I'd try that first before investing in a commercial version of what you can probably make yourself with Steve's published designs.

The 11 Turns on 2x (stacked) FT240-52 cores is probably the closest to an 'ideal' balun you can get, it is however a bit more costly to purchase as you need 2x 52 material cores.  However, if wound with teflon coax, it should be good for well over 2kw continuous into reasonable (SWR < 5:1) loads. 

The current 11T/2xFT240-52 Balun I use tested fine (no heating or insulation breakdown) at 1.3Kw into my dummy load.  It has not failed in service at 400 Watts PEP with ANY load.

By comparison, my a commercial Kenpro '1Kw CW' balun I had failed instantly when I tried putting 400 Watts PEP into a non resonant load.

I can't stress enough how much the Amateur community owes Steve G3TXQ for his work testing various designs and publishing them. Thanks Steve, hope you're well!
« Last Edit: January 15, 2017, 05:33:54 PM by VK3BL » Logged

J.D. Mitchell BA  - VK3BL / XU7AGA - https://www.youtube.com/ratemyradio - Honesty & Integrity
N3DT
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« Reply #34 on: January 15, 2017, 05:55:37 PM »

You can get those 240-43 ferrites from Mouser at a lot better price than Fair-Rite. I can come up with a number if I try. Let me look at my previous orders. I got 6/8 of them as I remember. You can also put them in multiple places along the coax. Especially at the entrance of the coax to the house, not just at the antenna. I use them, but my antennas are at least 120' away from my house and the shack is mostly underground, so that helps a lot, I have no rf in the shack with an 80B. Can you move your station to your basement? It actually may help. I like TXQ's choke plans, but then most of my coax goes underground to my shack so that also helps.
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KB1SNJ
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« Reply #35 on: January 15, 2017, 06:05:58 PM »

 thank you yes any source and part number information would be great. I did notice that Amazon has them for about ten bucks including shipping but if I get an order from Mouser I can be more confident of the authenticity and combine the shipping of a larger amount of them. and I saw that the comment that the number 52 toroids, doubled up would be ideal I'm not exactly sure why but it sounds like the 43 would be okay too.

 as to moving the shack to the basement,  I wish I had a basement, that's the one thing I really don't like about my house and probably the main reason that I hope to have a different house someday there's no basement and the house is extremely small. On my last house we actually installed a basement. Funny story an acquaintance of mine who moves houses stopped by and casually suggested that we could lift the house, move it, and when I have a hole with four concrete walls he could put it back. Said he could do it "next Wednesday". So I said "ok". The following Tuesday by the time my wife got home from work it was a little bulldozer and some iron beams sitting on my side yard and she asked what it was for I just told her don't worry about that.  But tomorrow when you come home from work the house may look a little different.  Oh It did! 

But our current house is built on a slab and that's not an option. Besides I'd really like to prevent RF flying around all over the place where it's not supposed to and protect the consumer electronics etc.  I really like the idea of any emanating RF to come from the antenna in the direction that it is supposed to go, and learning something in the process!



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NN2X
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« Reply #36 on: January 15, 2017, 07:45:28 PM »

SB 220!
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KB1SNJ
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« Reply #37 on: January 15, 2017, 08:46:58 PM »

SB 220!

Whats the main difference with the SB200?
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VK3BL
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« Reply #38 on: January 15, 2017, 10:42:35 PM »

thank you yes any source and part number information would be great. I did notice that Amazon has them for about ten bucks including shipping but if I get an order from Mouser I can be more confident of the authenticity and combine the shipping of a larger amount of them. and I saw that the comment that the number 52 toroids, doubled up would be ideal I'm not exactly sure why but it sounds like the 43 would be okay too.

Have a look at Steve's graphs.  The 2x52 has a wider bandwidth and handles more power.  The 1x43 is very broadband for a single core, but not as much as a 2x52 stack.  Cost difference, at least here in VK, however.
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J.D. Mitchell BA  - VK3BL / XU7AGA - https://www.youtube.com/ratemyradio - Honesty & Integrity
KB1SNJ
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Posts: 139




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« Reply #39 on: January 15, 2017, 10:54:17 PM »

Was JUST looking at that!  Smiley   But I'm not quite sure which way the colors go, not sure what values on the color key at the bottom. is that resistance to common mode current, and higher (such as green) is better?  So theoretically all green from 160-10 would be ideal?

also, do these cores come in different sizes? is the FT240-43 also a size as well as compound? The chart mentions turns and coax type for example 17 turns of RG58, so I need to get a large enough toroid core to accept rg58 17 times. I just dont know if the FT240 is a size spec or if I have some math to do. I suppose I could just cut out some cardboard with 35mm ID, get some RG58, and see that way!

The chart represents apparently a lot of work as u said, and it is very helpful once I can interpret its basics.  

sorry for the dumb questions and thanks for the info. if I can get the RF situation acceptable then its back to the amplifier choice. the 80b seems to get a lot of votes as does the old SB's


thank you yes any source and part number information would be great. I did notice that Amazon has them for about ten bucks including shipping but if I get an order from Mouser I can be more confident of the authenticity and combine the shipping of a larger amount of them. and I saw that the comment that the number 52 toroids, doubled up would be ideal I'm not exactly sure why but it sounds like the 43 would be okay too.

Have a look at Steve's graphs.  The 2x52 has a wider bandwidth and handles more power.  The 1x43 is very broadband for a single core, but not as much as a 2x52 stack.  Cost difference, at least here in VK, however.
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VK3BL
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« Reply #40 on: January 16, 2017, 12:30:17 AM »

Was JUST looking at that!  Smiley   But I'm not quite sure which way the colors go, not sure what values on the color key at the bottom. is that resistance to common mode current, and higher (such as green) is better?  So theoretically all green from 160-10 would be ideal?

also, do these cores come in different sizes? is the FT240-43 also a size as well as compound? The chart mentions turns and coax type for example 17 turns of RG58, so I need to get a large enough toroid core to accept rg58 17 times. I just dont know if the FT240 is a size spec or if I have some math to do. I suppose I could just cut out some cardboard with 35mm ID, get some RG58, and see that way!

The chart represents apparently a lot of work as u said, and it is very helpful once I can interpret its basics.  

sorry for the dumb questions and thanks for the info. if I can get the RF situation acceptable then its back to the amplifier choice. the 80b seems to get a lot of votes as does the old SB's


1) Green 160-10M would be ideal, correct

2) They do, but FT240 means its a 2.4" diameter core, so its not as hard as you might think.

No worries Smiley
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J.D. Mitchell BA  - VK3BL / XU7AGA - https://www.youtube.com/ratemyradio - Honesty & Integrity
W8JX
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« Reply #41 on: January 16, 2017, 04:52:48 AM »

SB 220!

Whats the main difference with the SB200?

The 220 uses a pair of 3-500z tubes vs a pair of 572's in 200. The SB 220 can make about 1000 watts out without much fuss and is only limited by its power supply (voltage and current)from being a true legal limit amp. (when it was built/designed the limit was 1000 watts)
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Ham since 1969....  Old School 20wpm REAL Extra Class..
N3DT
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« Reply #42 on: January 16, 2017, 07:53:52 AM »

Sorry, yes, FT240-52, I was relying on my defective brain to remember. Mouser PN 623-5952003801. If you look at TXQ's chart, the black/green bar is the one you're looking for, but that doesn't mean it won't work outside that range to some degree. FT=ferrite torroid, 240=2.4" as was said and -52 is the mix. You can pick up a fairly recent ARRL Handbook for a few bucks and there's a wealth of information in there about the Iron core and FT's, as well as lots of other good radio information. I see the Mouser price has gone up, seems I got them for around $6 in 2014. I also would suggest getting some RG400 off ebay for a few bucks to wind the 2 cores, that way, they'll handle anything you can give them and you don't have to worry about melting the coax with soldering. I use the 4" square weather proof electric boxes from Lowes or HD to put them in with #10 SS hardware for the antenna and SO239 for the coax. They're a bit tight but do-able. Larger boxes are available, but the price goes up too.

You're in a tough situation. No amount of reduction of the RF on the trans line or other things is going to stop the antenna from radiating into your house because the antenna is so close, even with a directional antenna. Vertical separation is your best bet. You might want to consider just running lower power and using the most effective antenna you can get up and dealing with it until maybe your situation changes. Lots of people use low power as a challenge. You might also consider a Mag Loop for RX and transmitting on something else, but with low power the Mag Loop is a cheap (home brew) alternative too. Try to get up different antennas to see what works, there's never enough antennas. I once had an inverted L that was right outside my shack and it too had horrible RF in the shack with just 100W, especially on the higher bands. If I were you, I'd concentrate on the RX end. If you can't hear them, you can't work them. Good propagation is your friend also.
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KB1SNJ
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« Reply #43 on: January 16, 2017, 08:18:18 AM »

thanks for the advice.  it seems often I can hear them and they cant hear me, or can barely hear me. as a result of information in this topic I figure on lower power but definitely wish to try more than 100w. 

also, if I could erect a free standing vertical, I could use the front yard but there's my house power coming across there so it would have to have at least a couple guys to prevent ever falling that direction (right?). of course if fiberglass then would that matter?

at any rate, I think I need to learn how to stop CM at the feedpoint and with that chart and the toroid info I am almost there. 

question: if I wanted to apply two ranges on the chart can I make both winded-toroids and install in series? I think I can just want to ask.

 is there any other way that the feedline can radiate RF in my house, when there is a choke?
how can I know there is no CM coming back?



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W8JX
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« Reply #44 on: January 16, 2017, 08:41:36 AM »

thanks for the advice.  it seems often I can hear them and they cant hear me, or can barely hear me. as a result of information in this topic I figure on lower power but definitely wish to try more than 100w.

I know you have some coin in current vertical but it is a big part of your problem. Plug n Play verticals like that promise a lot actually deliver less and can have common mode RFI issues too by nature. And such a tall vertical is not going to have favorable lobes on 20m and above too. Before amp, scrap current antenna and try a different setup because adding power to current setup could cause a LOT of problems with RFI in your house and not really help that much. One more thing if you limited yourself to 40m for now and shortened antenna to 33 feet and removed 9 to 1 balun it should work pretty good without a tuner too. You could insert 9 to 1 and use tuner on higher bands and it would work better on higher bands being shorter too but given susspot cycle is declining 40m is a good place to be. 
« Last Edit: January 16, 2017, 08:47:39 AM by W8JX » Logged

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Ham since 1969....  Old School 20wpm REAL Extra Class..
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