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Author Topic: Station reality checks...  (Read 730 times)
KF4KLZ
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Posts: 53




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« on: September 29, 2005, 04:07:40 PM »

I am getting back into the game after a long hiatus - mainly due to work and $$$$.  I just bought an IC-706-MKIIG.  I used to use a ht and a homebrew groundplane antenna - the one in the arrl handbook.  Well, it was just 5w - now I have more watts!!

What should I be concerned about when using homebrew antennas with my new rig?  I don't want to blow it up.  I really enjoy making my own antennas and will continue to do so.  My next will ba a 2m/6m dual yagi.  

Secondly, how concerened should I be with putting in an RF ground?  I will not be on HF because I am only a tech.  

Anything else you all can suggest would be great.  I currently have the rig, aston 35a power supply and the homebrew antennas.

Thanks in advance!
Sean
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WB2WIK
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Posts: 20542




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« Reply #1 on: September 30, 2005, 08:06:53 AM »

Unless your station is sitting on the ground, and probably outdoors on the ground, you'll never achieve an "RF ground" for your equipment on 6m or 2m.  Which doesn't matter, since you don't need one.

VHF antennas either include their own RF ground planes (such as a "ground plane" antenna does) or are normally installed so high above ground that they're ground independent; most any common VHF antenna design already includes an RF current return path.  In the case of a ground plane, it's the ground plane radials.  In the case of a beam, it's the other half of the driven element.

A station RF ground doesn't do a thing for VHF operations.

You might want a good lightning ground, though -- and that would be *outside* your home, not inside it, and created by making the lowest impedance possible ground path from your antenna support to earth.  That won't help with the way anything works, it's just a good lightning damage prevention mechanism, as are good coaxial lightning arrestors, well grounded, which would also be installed *outside* your home.

WB2WIK/6
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KF4KLZ
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Posts: 53




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« Reply #2 on: September 30, 2005, 09:01:28 PM »

Thanks for the help!

What if I wan to tlisten on HF...should I put in a rf gound?  Obviously being a tech, no xmit.
Thanks.
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WB2WIK
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Posts: 20542




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« Reply #3 on: October 01, 2005, 04:04:09 PM »

You only need an RF ground on the station equipment when you have to return path for RF current, which is a pretty unusual situation actually (nowadays).

If you use an end-fed wire, for example: This is unbalanced, with no counterpoise or image plane.  It's like trying to light up a lamp using only one wire for an electrical connection.  To complete the circuit, so to speak, you can add a good RF ground to the station transmitter or antenna tuner, and half the current will flow through that, the other half through the wire antenna.  If you don't make such a connection, your equipment chassis is likely to be "hot" with lots of RF (voltage) because it hasn't any place to go.  You know what they say about "potential" with no return path -- it's "not very bright" (as in a very dim light bulb, connected by only one wire).

But if you use a dipole, or a vertical with radials, or a loop, or any number of most common HF antennas -- for receiving or for transmitting, doesn't matter -- you don't need an RF ground.

There's still a reason to have a station ground: For electrical safety (shock hazard prevention).  That's very important, but doesn't require an "RF ground."

WB2WIK/6
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KF4KLZ
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Posts: 53




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« Reply #4 on: October 01, 2005, 04:33:28 PM »

Good, I appreciate your help.  I plan to purchase or make a diapole to listen to code and fiddle to learn more.  Good to know I am heading in the right direction.  Thanks again.
Sean
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KF4KLZ
Member

Posts: 53




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« Reply #5 on: October 02, 2005, 01:12:33 PM »

I am slowly adding to my station.  I have an Ashton 35a power supply, IC 706mkIIG, homemade 2m ground plane and a few HF diapoles. Anyone have have an opinion on what to add next? Antenna tuner?
Thanks,
Sean
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AA4PB
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Posts: 12665




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« Reply #6 on: October 03, 2005, 06:48:17 AM »

How about some test equipment? Multimeter, SWR meter, antenna analyzer.
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WB2WIK
Member

Posts: 20542




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« Reply #7 on: October 03, 2005, 08:11:38 AM »

How about eyeglasses, to see the power supply is really an "Astron?"

Only kidding.

Great investment if you haven't already made it: Books and reference materials.  Lots to choose from, and the ARRL Bookstore on their website has many great choices.  Nothing like building a technical library to provide answers to all the questions you were about to ask.

WB2WIK/6
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AD5X
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Posts: 1426




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« Reply #8 on: October 05, 2005, 04:32:37 AM »

"What should I be concerned about when using homebrew antennas with my new rig? I don't want to blow it up."

I think that all modern HF radios have very effective SWR protection circuitry.  I know my IC-706MKIIG has transmitted into some terrible loads (accidentally, of course) with no problems.  The best way to do your initial tuning is to tune with low power, or use the 10-watt cw "tune" mode.  This results in very little stress on your finals.  I also like to use a resistive SWR bridge for tuning as well.  See my "Tenna-Tune" articles on my web page for resistive SWR bridges and easy ways to enable the 10-watt tune mode.

Phil - AD5X
www.ad5x.com
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WA4PTZ
Member

Posts: 528




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« Reply #9 on: October 07, 2005, 09:39:26 AM »

You might want to replace the crowbar circuit
in that Astron with a relay and an RC circuit
before the power flickers and the power supply
meltsdown. Their crowbar sucks.
73 - Tim
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KF4KLZ
Member

Posts: 53




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« Reply #10 on: October 08, 2005, 05:18:11 AM »

>>You might want to replace the crowbar circuit
in that Astron with a relay and an RC circuit
before the power flickers and the power supply
meltsdown. Their crowbar sucks.<<

What would this modification entail? Is it as simple as pulling out the crowbar and replacing the relay and RC circuit? Any soldering and cutting? Are there any plans/notes on this modification on the web?
Thanks! Sean
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AA4PB
Member

Posts: 12665




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« Reply #11 on: October 08, 2005, 04:45:10 PM »

The crowbar is there to protect the load against overvoltage caused by the failure of the regulator (usually the pass transistors) circuit. An overvoltage sensing circuit fires the crowbar. I can't imagine how a relay and R/C circuit could react fast enough to save your rig.
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