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Messages - Quietguy

Pages: 1 [2] 3 4 ... 12
16
Antennas / Re: Super Gain 9db 40m NVIS Antenna.
« on: March 24, 2017, 06:33:40 PM »
Thanks Wally, very informative! What's the book?

It's "Electronic and Radio Engineering", 4th ed, by Frederick E. Terman from 1955.  It was a college textbook still in use back in the mid-1960s.  It was used in some of my courses, which is why I happen to have a copy.  Sigh, yes, I'm that old and obsolete...

I can see that in my minds eye, but the gain they are speaking of in this article is going straight up !  Good for NVIS, bad for DX !

That was pretty much the author's point - reduce interference arriving at a low angle from foreign shortwave broadcasters on 40m and favor high-angle NVIS regional contacts.  I don't believe the term NVIS was used back in the '60s when this article was written, but they certainly were aware of the effect.  As DJ6KR mentioned in his post, the significance of this article is the reflector laying on the ground underneath the antenna wire directing more of the energy upward.  Terman's book (Figure 23-36) shows "Directive Gain" of about 8 at  a spacing of 0+ to about 0.1 wavelength and then steadily dropping to about 4 at 0.3 wavelength, where the plot ends.

The same figure has "Radiation Resistance" plotted at the same spacing scale, and it gets better as spacing goes up.  The downward sloping Directive Gain plot crosses the upward sloping Radiation Resistance line at a spacing of about 0.17 wavelength.  This yields a Directive Gain of about 7 and Radiation Resistance about 50 ohms.  That is probably the sweet spot for overall efficiency, but it puts the antenna up about 22 feet, which is still NVIS territory, but is much less convenient than 7 feet.  Additionally, Terman's figure is based on a reflecting screen beneath the antenna; 3 wires 6 feet on center may be a good approximation of a (40m) screen at 7 feet height but I wonder if additional reflecting wires would be necessary with higher antenna elevations, just because of the geometry.  At 7 feet the "screen" is wider than the antenna height, so would a 22 foot high antenna require a much wider "screen"?  I suspect it would to get the maximum effect.

Wally

17
Antennas / Re: Super Gain 9db 40m NVIS Antenna.
« on: March 23, 2017, 09:11:28 PM »
It is all about the reflector on the ground under the Antenna, I think.

Yes, I have a copy of Terman's book that is referenced in the article.  Terman discusses a "Half-wave Antenna with Reflector" starting on page 903 and derives the gain.  He shows plots of gain compared to radiation resistance as a function of antenna to reflector spacing.  Radiation resistance (and efficiency) goes way down with small spacing, while gain stays around 8 up to a spacing of about 0.1 wavelength (about 13 feet on 40 m) before falling off with increased spacing.  He says:

"In order to prevent incidental loss resistances from making the antenna efficiency very low, the spacing S should accordingly be at least 0.05 wavelength, and preferably 0.1 wavelength."

The article uses 7 feet, which is about 0.05 wavelength at 40 meters, but Terman's chart shows you would have better efficiency without losing gain if you made the antenna 14 feet high.

Wally

18
New To Radio / Re: Problem with antenna on 1 of 2 radios
« on: March 21, 2017, 06:02:21 PM »
With the working regular antenna that came with it, if I put my finger on the antenna and gently push in one of several directions, the incoming signal shuts off, as if the antenna has been removed. 

I haven't pulled a Baofeng apart to verify this, but it sounds suspiciously like the antenna connector is soldered directly to the edge of the printed circuit board and the connection is broken.  Since flexing the working antenna loses signal it sounds like it normally makes contact but any movement breaks the connection.  The odd antenna may fit slightly different from the stock antennas and deflect the connector enough to cause the problem.  This was a problem with the old Icom W32A dual band handhelds; an impact to the antenna could break the circuit connection and cause intermittent operation.

If you are comfortable with a soldering iron you can attempt to take it apart and touch up the connection or circuit traces leading to the connector.  At the price of a Baofeng you don't have much to lose.  If you transmit with the connection broken you may fry the output anyway.

Wally

19
Net Activity / Re: Preppers Calling Frequency.
« on: February 23, 2017, 05:16:24 PM »
I'm not sure such a frequency legally exists.

Only on 160 and 60 meters as far as the US is concerned.  Attached is a screen shot of the HF portion of the table I linked above.  Note that 80 meters is defined as 3.525-3.600 MHz and 75 meters is defined as 3.800-4.000 MHz.  40 meters is divided into two segments, 7.025-7.125 MHz and 7.175-7.300 MHz.  You are right, digital modes are not permitted in the phone allocations.

I believe this was one of the reasons the ARRL requested a rule change where the FCC would regulate by bandwidth rather than by mode, but I don't know what happened to that proposal.  There was a lot of objection because some people said they were just trying to turn all the bands over to "robot" digital stations.


Wally

Edit to add:  Full Members can't post images without approval now?  It says my screenshot is waiting for approval.


20
Net Activity / Re: Preppers Calling Frequency.
« on: February 22, 2017, 06:49:08 PM »
No, it isn't an ARRL Band Plan, it is in the FCC Part 97 regulations,  "97.305   Authorized emission types".  No 40 meter phone from the continental US below 7.125 KHz.  I took this straight from a government web site which has nothing to do with the ARRL:
http://www.ecfr.gov/cgi-bin/text-idx?c=ecfr&SID=336ab7469b61ecbfa15086dbf1bf2c59&rgn=div5&view=text&node=47:5.0.1.1.6&idno=47#se47.5.97_1301

Edit to add:  this link takes you to Paragraph 97.301 which details the limits for each ITU region.  Scroll down to Paragraph 97.305 for details.  Although the entry "7.075-7.100 MHz    Phone, image" appears to authorize Phone, footnote 97.307(f)(11) takes it away for the continental US:

Quote
(11) Phone and image emissions may be transmitted only by stations located in ITU Regions 1 and 3, and by stations located within ITU Region 2 that are west of 130 West longitude or south of 20 North latitude.

Wally

21
General Discussion / Re: Survival Radios, Really?
« on: February 02, 2017, 04:50:22 PM »
These go-boxes are good for disaster relief supported by an infrastructure, not for preppers on the move.

Or, they are good for the "radio operator" supporting a group in a retreat setting, if you happen to be a member of a group with a retreat.  For an individual on the move... not so much.  It goes back to the first thing people should do but isn't much fun, so it tends to be avoided:  define your realistic needs before obtaining the equipment.  Over and over again we see people on other forums asking "what radio should I get?  Is the Baofeng a good choice?"  Not one word about what purpose they expect the radio to serve, not one word about their terrain, not one word about who they want to talk (or listen) to...  IMHO it is very much like asking "how long is a piece of string?"  But if you ask them for details there usually is no answer.

Wally

22
General Discussion / Re: Survival Radios, Really?
« on: January 26, 2017, 06:17:52 PM »
Al, I am surprised that your agency needed more digital repeaters.

Often the problem is caused by going from analog VHF to digital 700/800 MHz systems.  Areas with terrain issues (those darn hills, valleys, canyons and mountains) - particularly rural areas without tall buildings - are not good candidates for replacing 150ish MHz public safety systems with 700/800 MHz trunking systems.  People tend to think of 150-160 MHz as line-of-sight, but that isn't strictly true.  There is lots of signal bouncing that goes on with VHF analog that doesn't happen with UHF trunking systems.  Many cities have been disappointed when their shiny new trunking system reduced their coverage area.

Wally

23
Morse Code / Re: cw on 2 meters
« on: December 31, 2016, 11:54:02 PM »
I recently configured my Buddipole for 2 meter verticle and began searching for signals in the 144.05 to 144.10 CW area.

I haven't tried it, but I believe most CW and SSB work on 2 meters uses horizontally polarized antennas rather than vertical as is customary with repeaters.  If that holds true in your area you are giving up a lot by using a vertical antenna, try a horizontal configuration.

Wally

24
Technical Corner / Re: How to solder aluminium rods?
« on: December 12, 2016, 03:25:59 PM »
I ended up using a mechanical connection.

Yes - I should have made my comment clear that the oxidation inhibitor paste was for mechanical connections between aluminum and copper, not soldering.  Copper and aluminum mechanical connections aren't reliable because of oxidation.  That was a major problem in the early days of aluminum house wiring connected to copper terminals on receptacles and switches.  I was suggesting using the paste along with a copper saddle straddling the joint.

Sorry if I confused the issue...
Wally

25
Technical Corner / Re: How to solder aluminium rods?
« on: December 11, 2016, 09:32:54 PM »
It is very difficult to solder aluminum and you can't really "slightly melt" it because aluminum does the transition from solid to liquid very quickly and you end up with a puddle.  The best way is welding with a shielding gas because aluminum quickly oxidizes.  I assume you are trying to butt the ends of the rectangles together and make them electrically continuous.  There is an oxidation inhibitor paste designed for making aluminum to copper joints in electrical wiring.  Maybe you could clean the oxidation off the rod ends, apply the paste, and make a saddle splice out of copper spanning the joint.  The cleanest solution is to find a friendly welding shop and have the ends welded.

Wally

26
General Discussion / Re: Contest Mayhem.
« on: November 01, 2016, 05:01:59 PM »
You should see the peeing match about this on eham.net's QRP forum.
I quit reading all of eham's forums several years ago because of the trolls and general lack of civility.  I don't enjoy associating with assholes in Real Life so I decided I didn't need to associate with them in Cyber-Life.

Wally

27
Digital Modes / Re: HF APRS
« on: October 08, 2016, 08:58:40 PM »
Interesting.. Especially if the message can be stored upon reception and read later.

Yes - it's just data; APRS allows a limited amount of free-form text.  The radio/TNC feeds what it hears into a computer as ASCII text and what you do with it on the computer is up to you and the program you run.  People are using Raspberry Pis and RTL-SDRs to process APRS data using Linux software.  I have been involved in an application where we used a 2m radio, Kantronics TNC and Windows laptop to process specific APRS data and upload it to a web server for plotting.  The laptop sits there 24/7 running a cron job where it throws away the stuff we don't want and uploads the stuff we do want to a hosted server.  PHP scripts on the web server process the data for plotting on demand.  We already had the equipment but I'm thinking about replacing it with a RTL-SDR/RPi combo just to free up the "real" radio, TNC and laptop for other use.  It seems kind of a waste to keep a perfectly good 2m mobile sitting there doing 24/7 receiver duty.

Lots of potential, but some creative DIY interfacing may be required for non-standard applications.
Wally

28
Digital Modes / Re: HF APRS
« on: October 08, 2016, 06:58:14 PM »
APRS is a convenient protocol to send any kind of short data packets - short "text" messages, battery/system voltage, ambient temperature, equipment temperature, river/lake levels... a custom interface can be built which sends alarm system status of a remote site.  It will tell you when the tripwire on the trail leading to your cabin is tripped and it will monitor the status of your gates.  All it takes is a little DIY and you can get away from the range limitations of unlicensed wireless devices.

Backpack survivalism is not in the cards for some of us, so a little extra infrastructure can be worth the time and effort.  It becomes a force multiplier for those of us who, because of age or infirmity, can no longer throw the ruck over the shoulders and march off into the sunset.  EMDV.  (Everyone's Mileage Does Vary)

Wally

29
I just did a little looking around and it has been around a year or so with lots of information on various sites, including Miklor: http://www.miklor.com/KT8900/ .  Eham gives it the usual mixed reviews from "the greatest thing since sliced bread" down to "pure junk".  Oddly enough it is available on Amazon for $85 with programming cable and free Prime shipping.  There are a few known issues, so read about it before ordering.

Apparently programming is supported by Chirp and there is a jack in the rear just above the power cable.  It is kinda hard to see in the Banggood photos but if you look close it is there. 

Wally

30
Classifieds / Re: MTR5b, American Morse mini-Paddles, Kayaker Case
« on: August 07, 2016, 08:55:58 PM »
if I have to pay for the plane ticket, I can think of a couple redheaded girlfriends who might take me up on such an offer ;-)

Well, yeah, but are they Morse code wizards?

Priorities...
Wally

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