View Full Version : 28.3MHz ???
01-24-2009, 02:54 PM
Ok, here is a silly question from a new-b.. I have an Icom IC-7000 Transceiver capable of the HF bands. I have installed a 10m dipole in my attic, I have an LDG 7000 tuner matched to the IC-7000 and I still can not receive any signals on the 28.3 to 28.5 MHz (USB). Is the problem most likely the antenna in the attic or am I missing something basic? Thanks for the help..
01-25-2009, 06:42 PM
Good for you. Glad to hear you're getting on HF.
First, tell us about your dipole. Did you cut a length of 14GA copper wire per the formula: length in feet=492 divided by frequency in MHz? Is it in the attic as high as you can get it and the wire isn't touching anything? If possible, it should be running with the length of the dipole in a north-south direction.
Our time to play radio is valuable. Go to the DX Summit spotting software (http://www.dxsummit.fi/). Click on "custom spots" and pick 28MHz and you'll get an idea where the propagation is.
The sunspot cycle is in the tank but that should be changing very soon. Those of us with "modest" antennas suffer more than the guys with beams and tall towers. Hang in there. Now is a good time to check out your system to be sure all is working fine.
Do you have any way of checking your SWR? If your transceiver doesn't have a meter in it, does your tuner have one? It would be nice to know that you have a low SWR and that you're not losing your signal due to something out of wack with the coax, connectors, or the dipole itself.
Keep listening. Watch the DX Summit as it will tell you who's talking to who and on what frequency. That will allow you to tune to that frequency to see if you hear one or the other or both of the stations.
Keep the questions coming. HF is a lot of fun. And with the sunspot cycle climbing to its peak, you're in for a lot of contacts on the radio.
01-25-2009, 11:14 PM
Bruce, Thanks so much for the reply!! I have tried 2 dipols, the first was one which I made from scratch, 12ga "high strand count" premium grade speaker wire insulated approximately 16'6" total length. My feed to the attic is RG-58 plenum rated with a BNC connector in the attic to enable an easy connection with a coupler and a PL-259 at the tuner. The antenna is mounted as high as I can get it in the attic, I am however in a ranch but the peak is about 20-25' above grade. My roof does slope on the north and south side so I am sloping the antenna at about 45* from the peak, I am sloping on both sides (inverted V).. The second antenna is the exact same design with few exceptions, it is a dipole that I got from LDG with the tuner. It is 14ga bare copper 7-strand non insulated, same RG-58 lead with BNC connector.. Do you think I may be better off running the antenna east to west without the inverted V? If I flatten out the North / South it will only be about 14' above grade. I am on a hill, not the highest house around but still pretty high. I did check the SWR without the tuner and it was off the charts, when I connected the tuner and hit the tune button on the Icom IC-7000 it locked in and dropped the SWR to between 1 and 1.5.. Thanks again for your help and I look forward to learning more... 73 for now..
01-26-2009, 10:52 AM
I will echo Bruce's comments about the sunspot cycle. The only 10M contact I have made in the last 5 years was just last summer when I managed to talk to California, and even then the QSB (Fading signals, either fading in our out or both) was intense.
The reason Bruce suggested the dipole point north and south is so you can get the best radiation to where you most likely will talk. The ends of the dipole antenna represent nulls, or points where the radiation will be extremely low if at all. So north-south direction will give you good radiation toward Cali and the east coast, whereas east-west setup would have you talking to Canada and South America. Just a matter of preference and possibly the most success right now.
One question, do you have a balun at the feedpoint of the antenna? Meaning, you say you have the pl-259 at the tuner, and the other end you have a BNC connector. I get the PL-259, that's easy. Is th BNC connector on the other end how the dipole from LGD came? I am just curious, because most times a simple dipole can be made by soldering the center conductor of the coax to one side of the dipole, and the shield to the other. I am not saying what you have done is wrong in any way, just wondering about the setup.
My next point would be the SWR without the tuner. I suggest anyone making a dipole trim it to the formula, and test it without the tuner, if possible. If your SWR w/o the tuner is greater than 5:1 or 6:1, or basically shoots off the scale, then something is wrong. I would first guess that maybe a math error was made, or the wrong frequency was used in the formula when compared to the actual frequency used to check SWR. The reason I suggest this method of testing is because if you try the antenna on your radio at the precise frequency you cut your dipole to length for and there is that much of a mis-match, then more calculating is in order.
I will regress a minute. Just because an antenna has a high SWR is not always bad. However, it is the most basic method to see how efficient the setup is performing. The radio you have (and most HAMs use) are set to see 50Ώ (ohms) at the output for the antenna. If the antenna is not at a 50Ώ (or within 10Ώ is good), then the mis-match causes output power to be lost in the form of heat. The tuner doesn't do anything but help eliminate that mis-match so that the radio thinks it sees 50Ώ. The tuner is basically a trick so that the radio doesn't fry its internal components when the mis-match occurs. My point? If you are trying to operate single side-band on 28.3 mHz, and your SWR is at infinity, the tuner may be able to "trick" the radio into thinking that there is a match of 50Ώ at the radio, therefore allowing the radio to put out maximum (100W in the case of the IC-7000) power. However, at a SWR reading of infinity, you may only be putting out 5W or less at the antenna. There is a formula for checking how different the power will be based on SWR that I will give if you want it.
Back from regression. If your antenna is not tuned (cut to length to achieve somewhat reasonable SWR first at a very specific frequency, then use the tuner to allow for moving up and down the band from the initial frequency) correctly, you may not be hearing anything for this reason as well. Any piece of metal will pick up radio waves, but remember that polarization as well as a list of other factors will determine the best antenna for receive.
My gut feeling guess? There is nothing on the 10M band, or no propagation (lack of sunspots) to help what might be on the air be heard well.
My suggestion? Lets get you a 20M dipole to test. Just hang it from a tree on a Saturday temporarily. Then listen to the 20M band on a weekend. My guess is that you will be hearing things all over the place. Then we have to get you up to speed with CW (or get you to upgrade your license) and you can set up dipoles for 20M, 40M and 80M and talk to a whole bunch of people.
Any of this help?
01-26-2009, 08:09 PM
Nathaniel: Thanks for the info!!! The LDG Dipole was just a length of wire with 3 plastic insulators (a freebie for buying there tuner). I took the 50ohm coax and soldered the center to one half and the shield braid to the other half, this is a short section (about 3') which I then installed a BNC connector for quick release. My thought is that I would like to have an antenna which I could take with me in the field for a mobile setup.. The feed to the attic from my shack in the basement is about 50 to 60' of coax... I was really surprised to see the SWR as high as it was and think you are correct about my need to get the SWR more in line without the tuner, I went off of the paperwork sent with the LDG tuner and I do not know how they came up with 16'8" for 28.1Mhz.. Per the 492 rule - 28.1 it would be 17.51... So, I will work on correcting the SWR without the tuner and see if that helps.. I am studying for the General now and hope to have it soon, I need to brush up on my math skills a bit more. I really like your idea on the 20m dipole!! I will make one up and run it outside to see if i can get anything on it...Thanks again for all your help!!!! :)
01-26-2009, 09:43 PM
Yeah, sounds a bit fishy to me.
Just to be sure we are talking about this right. This is what your dipole basically looks like, with each leg around 8 feet long, correct?
11836(Ignore the loading coils for our questions)
Or is each leg equal to the 16 feet you mentioned?
01-27-2009, 08:06 AM
That is correct. Each leg is aprox. 8.3'..
I did check to see where the Length calculation came from, there are a few sites one in-particular that calculates Dipole length at 468/MHz and then suggests deducting an additional 5% for an inverted V design.. Here is the link..http://http://www.hamuniverse.com/dipivcal.html Another suggests 464/MHz, all very interesting, they all state that this gets you in the ball park and that they need to be tuned to the specific frequency... I was looking at an MFJ-269 analyzer to help with antenna setup, do you have any experience with these? Thanks again!!
01-27-2009, 09:16 AM
I think you are correct. The ARRL handbook uses the 468 (and that is the formula on the test) number to calculate the length of the dipole. The problem with that number is that too many people get anxious about cutting and cut exact length, then they end up being too short after they use wire length to wrap around insulators etc. From the insulator to the insulator, the 468 number is good; to calculate what to cut before wrapping the insulators the 492 is good to start out.
The MFJ-269 is about the most comprehensive antenna analyzer you can buy in the US. Bruce has the better Japanese version, made by Kuranishi Instruments (http://www.eham.net/reviews/detail/3629) that is smaller and better rated. It is also $500 used.
I am currently looking at getting a used (READ:Thrifty) MFJ-259B so I can do exactly what we are talking about. These meters will tell you when connected to your antenna the resonant frequency the antenna will radiate most efficiently at. (Did I just end a sentence with a preposition?) Until then, my suggestion is to tune to the freq you believe the antenna to be tuned to, and check the SWR. No good? Move 10kZ up or down the band. Check the SWR again. Any better? Try the opposite direction, still 10kZ away from the starting freq. Better? Keep going until something starts to decrease/increase the SWR. Then fine tune.
However, if you get the MFJ-269 before I get a MFJ-259B, you may become my best friend. :D BTW, I have a 20M dipole made, not sure what the freq is to start, but you can borrow it if you like, just have to solder coax to it. Or you could come over one day and hook your IC-7000 to my HF mobile antenna. I use a Hi-Q 5/80 RT. We can tune in 20M some weekend day and see how well that 7000 really does. That is my next radio after i sell my kidneys. :lmao:
Info on the Hi-Q Antenna (http://hiqantennas.com/):
The Hi-Q-5/80 ALL SS (All Stainless Steel)
Remotely Tunable/Motorized (RT)
6 thru 80 meters
The CAP and Base are Cad Cam designed and CNC machined out of Stainless Steel. The lower mast is 1.5" dia. SS tubing with SS mounting base with 3/8-24 thread. Cap has also 3/8-24 threaded hole for the whip. The Hi-Q-5 is designed to be used with the Hi-Q CapHat for MAXIMUM radiation Efficiency on 80 M. It is optimized for the 80 M band, however it performs great on the 60-40-20-15 and 10-meter bands. Two versions are produced, military, Hi-Q-5M and the Hi-Q-5/80 for the ham bands
It is extremely rugged with a LIFE time guaranteed. 12 or 24 VDC, remotely tunable.
Antenna height: 3 ft, no whip
Antenna weight: 7 lb (6061T6)
01-27-2009, 09:24 AM
You're on the right track. You need what all radio operators need right now and that's the sunspot cycle to get closer to its peak. That time should be soon.
When we first moved to the Cayman Islands, I put up a dipole to get on the air and work the world from our somewhat rare DX QTH. As hard as I tried, the only QSO I made was with a sailboat passing by the island. This was about 1987 during what is still considered to be the most powerful peak to any sunspot cycle. I quickly replaced the dipole with a 6 element tribander and it was like the switch was flipped on. Signals galore from all over the world.
Nathaniel has a really neat vertical HF antenna that mounts to his 80 series rear bumper. Such an antenna will out perform a dipole and it will be difficult for cranky neighbors to complain about because it's a moving target!
I guess the moral of the story is the old radio one liner, the best antennas are the ones with the most metal you can get as high above ground as you can get it.
Even if you live in a covenant controlled development, there are reasonably priced antennas out there that you may wish to keep an eye out for that will pack a little more punch than a dipole and may go unnoticed by the neighbors.
Watch the DX Summit, too. Watch the solar flux numbers as well as the A and the K indices. One day soon they will begin to climb to the cycle peak.
02-15-2011, 09:34 AM
FIRST X-FLARE OF THE NEW SOLAR CYCLE: Sunspot 1158 has unleashed the strongest solar flare in more than four years. The eruption, which peaked at 0156 UT on Feb. 15th, registered X2 (http://spaceweather.com/glossary/flareclasses.html?PHPSESSID=accaq7b7oal2msrggbo95b6g31) on the Richter scale of solar flares. NASA's Solar Dynamics Observatory recorded an intense flash of extreme ultraviolet radiation, circled below:
X-flares are the strongest type of solar flare, and this is the first such eruption of new Solar Cycle 24. In addition to flashing Earth with UV radiation, the explosion also hurled a coronal mass ejection (CME) in our direction. The expanding cloud may be seen in this movie (http://stereo.gsfc.nasa.gov/browse/2011/02/15/behind_20110215_cor2_512.mpg) from NASA's STEREO-B spacecraft. Geomagnetic storms are possible when the CME arrives 36 to 48 hours hence. Stay tuned for updates.
02-15-2011, 11:32 AM
Sweet! I've been waiting a while for that damned ball of fire to get crazy again.
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