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K5UJ
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« Reply #50 on: June 03, 2011, 09:24:51 AM »

Some of the physically small antennas written about here and there may provide some satisfaction for contesting and dx chasing but one must keep in mind that these activities involve short QSOs, and narrow bandwidth efficient modes.   Firstly, if all one has space for, is a physically small antenna then he should go with that and hope for the best.  But for AM the deck is stacked against us (which makes for a challenge I enjoy) with its poorer S/N due to a wider passband on receive, and lower power density on transmit due to the spread of the same wide bandwidth and intelligence in the lower powered sidebands.  The beautiful sound of AM has a price in other words, making a good antenna all the more important if one is going to have a satisfying experience.  To get back to the original questioner I think this was one of the reasons why  K1JJ was emphasizing the importance of having a good antenna.   There is a tendency to give a newcomer a rosy picture but I will not lead anyone to believe low power and a small loaded antenna is anything other than a beginning.

To be sure, there is a lot to learn about antennas from the contesting and dxing community, expeciallly in the area of tower construction, feedlines, modeling, receive antennas, phasing and other topics so I am not discrediting them by any means.  Ultimately, AE1CT will have to experiment, which can be a lot of fun itself, and reach his own conclusions.

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« Reply #51 on: June 03, 2011, 09:57:19 AM »

Completely untrue. In the past 73, CQ and Radio and other rags had technical articles - often superior to those of QST. The west coast handbook was better than the ARRL handbook too.




The NCJ is about the only place you will find quality articles published. Contesters take performance seriously.


Looks like further fragmentation of technical information published by the League.  Once upon a time all the technical information was published in QST, the Handbook plus, for those interested, the speciality handbooks (antennas, SSB, Hints & Kinks, mobile etc). Now you have to subscribe to three periodicals in addition to purchasing the speciality publications to get all the technical articles... and the least fruitful of these is QST, the default membership publication.  However, lately I have seen some improvement in the technical content in QST.
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« Reply #52 on: June 03, 2011, 10:04:00 AM »

The 43 foot vertical is popular because it can be used on 40-10 meters when fed with coax and tuned with a tuner in the shack. If the coax is of reasonable length, the loss will be acceptable. Making it work on 160 and 80 is possible but not nearly as simple.


Dave, the 40-43' has been popular for a long time and was really popularized when the US was given the  full band and 1500W in the late 70's. Then 160 was included on DXpeditions an the 43' gained popularity. W1FV's contribution was to produce a high performing 4 Square with shortened radiators and only 1/8 wave spacing on 160 using the 80M array he had been already using.

Yes, 160 propagation is amazing at times, Ive worked 13 countries with 100mw on nights when every EU with 100W or less to a wet noodle was at least 20 over S9.

I was looking at a full 1/4 wave L for my 500 KHz antenna and didnt like the modeling results with only 170' being vertical. Efficiency and bandwidth were better with 4 140' sloping top hat wires than the roughly single 325' top wire.

Carl
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« Reply #53 on: June 03, 2011, 10:56:16 AM »

I modeled Donís dipole over real ground. The feedpoint impedance was something like 18 Ė j1000. I think I forgot the Ė sign when entering the Z into TL. Now I get 9 + j290 at the end of 119 feet of 600 Ohm OWL. Adding 60 feet yields 62 Ė j1500. That will teach me to do this stuff late at night!

Quote
Taking the one where we disagree first; a short dipole on 80m at 120ft will have a radiation resistance between 12 and 16 ohms and look capacitive on 160m. Roughly halfway down the 119ft OWL section it will look purely resistive at 6 to 8 ohms. If the OWL is 500 to 600 ohms the low resistance at the halfway point will be transformed to an inductive reactance in series with a low resistance at the bottom because itís a further one-eighth of a wavelength to that point.
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« Reply #54 on: June 03, 2011, 12:54:48 PM »

Steve, glad you got the modeling sorted out. Thatíll teach you to be too reliant on computers! From your figures it looks as if Don will need larger series capacitors than I suggested, and a smaller shunt inductor.

Carl, when I first got on 160m in 1963, the 41ft vertical was already very popular with British 160m DXers because they could use it all the way up to 20m with a modest ground system from quite back small gardens. They even got some gain on 20m because the antenna was 5/8 wavelength on that band, Most switched matching circuits manually at the base to change bands because they didnít have to walk far to do this. They had no interest in working other UK stations on AM apart from comparing notes on 160m with their local rivals, and the vertical was ideal for that, of course, because of its strong local ground wave. Obviously, this doesnít fit the bill for Gary (AE1CT) because heís interested in working around New England on 75m AM, as well as operating 160m, and the skip zone with a vertical is not going to be conducive to that. I think it was Fred who said that those using this ďmagic 43ft antennaĒ have to use a top loading wire to get it to work reasonably well. Do they add enough to produce a reasonable amount of NVIS, or is it just to make the vertical more efficient for ground wave and low-angle, sky-wave work?

Iím very sceptical about this 4-square arrangement, Carl, because with only 43ft verticals and 1/8 wavelength spacing on 160m the array gain would probably be offset by the increased loss in each vertical compared to one vertical with no interaction. It will obviously help on receive because of the directivity, but there are easier ways of getting directivity for receive only. If you get very little increase in transmit gain, it seems hardly worth going to all the effort of a 4-square array unless you already use it on 80m. Anyway, it has no bearing on Garyís predicament, so we ought not to be discussing it on this thread, interesting though it may be.

K5UJ is right to be concerned that Garyís desire to operate AM from a small plot is going make things harder for him. I agree, but itís not going to make things impossible, and heíll get a tremendous amount of enjoyment out of being able to put out a half-decent signal over 200 to 300 miles with modest power. If I had to describe a typical British 80m AM station these days, he would probably be using a G5RV with the centre at about 25ft and a DC input of 50W. These guys have no trouble working each other during the early mornings and late afternoons, and signal strengths improve enormously as darkness approaches and the D-layer attenuation fades away. Conditions do become a problem for them at noon during periods of high sunspot activity when D-layer attenuation is high, or the E-layer ionization is so strong and flat that nothing much gets reflected back, but otherwise they have great fun and get plenty of enjoyment from their hobby. Some of them get on 160m in the winter by adding end loading to their G5RVs. If youíre still monitoring this thread, Gary, I hope what Iíve described here gives you some encouragement.

Dave.
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« Reply #55 on: June 03, 2011, 01:57:31 PM »

Did I just hear someone mention 'a reasonable amount of NVIS from a vertical'? I'm aghast!

Walt
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« Reply #56 on: June 03, 2011, 02:07:44 PM »


Don, if you only need to shift about 5 kHz before you notice a significant increase in SWR, then your system -3dB bandwidth could be as low as 15 kHz. This corresponds to a system working Q of 127!!!  The Q of your antenna and feeder system alone ought to be 40 to 50, so you should to be able to gain an increase in bandwidth of well over 2 if you use the simplest matching arrangement possible. Thatís what Iím suggesting.

My mental picture of your suggestion would be a balanced tuner, with a coil and two variable capacitors. Each variable would be in series with one of the legs of the tuned OWL that feeds the dipole, with the other side of each cap connected to one end of the coil. The transmission line from the shack could be coupled to the tuner either by (1) a separate link tightly coupled and physically located at the mid-point of the coil, with the number of turns adjusted for the best match at resonance to make the transmission line from the shack as flat SWR-wise as possible, or else (2) by tapping the transmission line from the shack directly to two points symmetrically located about the mid-point of the coil (same basic configuration as separate link coil, except the main coil would be used as an autotransformer). The spacing between taps would be adjusted for the best match. Do I get the picture correctly?

Another possibility with the above configuration would be to split the coil and insert the untuned transmission line from the shack to the gap, and adjust the capacitors and number of turns in each half of the coil for the best match, making it sort of a balanced L-network.

Any one of those basic configurations ought to work equally well with 50Ω coax or with balanced (440Ω) OWL serving as a flat untuned line running back to the shack, with appropriate adjustments to capacitances and inductances.

Attached is a photo of the present 160m dipole tuner. The link-coupled coil is seen mounted vertically in the corner, and next to it is the split stator capacitor, with the worm-drive and reversible motor mounted on the top end. The shafts at either end of the variable cap are coupled to 90į drive mechanisms, each of which is coupled to two more variable capacitors mounted horizontally along the top and bottom of the box and used to resonate additional tuners.


* motor and 160m dipole tuner.JPG (1166.53 KB, 2576x1716 - viewed 1121 times.)
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« Reply #57 on: June 03, 2011, 02:09:26 PM »

No, but you might just have read something about it, Walt.

And, be clear, the reference is to a single horizontal top-loading wire added to a vertical, in which case it becomes an inverted-L with 43ft of vertical and whatever length of horizontal wire. Some NVIS will come off this wire and the amount will increase as the wire is lengthened. I was enquiring about whether they did it to produce some NVIS or just to pull the current more up into the vertical section to increase the efficiency.

Dave.
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« Reply #58 on: June 03, 2011, 02:23:37 PM »

Hi Don,

You just caught me on the hop typing a reply to a mischievous comment by Walt.

No, the 50-ohm coax can be connected straight across the small inductor since you can alter its inductance and tweak the capacitors to get a perfect match at this point. If you run your 50-ohm coax underground to the bottom of the tower you might get away without using a balun, otherwise,heaven forbid, you might have to use a W2DU choke balun! If you've got a hefty ferrite core lying around you could go for a W1JR choke balun instead.

That tuner look impressive. It'll be a shame if you can't find another use for it, but the existing application doesn't really require it and actually makes the situation worse.

Steve's simulation on a computer suggests that you might need larger series capacitors than my back-of-a-cigarette-packet calculations suggest, so be prepared for adding a bit more capacitance across your series capacitors in the prototype if necessary. His figures also suggest reducing the shunt inductance a tad as well, but that's pretty small anyway.

Dave. 
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« Reply #59 on: June 03, 2011, 02:37:51 PM »

Here is another shot showing the rest of the tuners and how everything is ganged together. I forgot to attach it to the previous message.

Walt and Dave, couldn't one at least approximately achieve NVIS radiation using a long vertical, several wavelengths tall? There would still be a sharp null straight up, but there would also be near-vertical high angle radiation that could illuminate very closely to the antenna.

Since my results using the 160m vertical as a half wave on 80m have been disappointing, consistently getting poorer signal reports at all distances including west coast USA and Europe than with the dipole (also a half-wavelength high), I have considered re-tuning the 80m 1/2λ vertical to make it a full-wave vertical on 40m. According to the theoretical charts, the main omni-directional lobes would be at about 50į take-off angle, which should work well for stations at distances a few hundred miles away in N America, useful during daylight hours, and maybe fill in some areas where the 80m dipole operating as a double-Zepp has nulls.  It's at least worth a try, since I have all the needed stuff on hand.


* front view.JPG (1169.31 KB, 2576x1716 - viewed 1138 times.)
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« Reply #60 on: June 03, 2011, 03:44:05 PM »

Don,

That's very odd about the half-wave vertical on 80m. You'd expect it to go great guns on 80m. I wonder what the ground conductivity is like around your property. You mentioned in a previous posting that you got better results 50 miles away on sky wave than you did on ground wave, which considering your power points to quite poor soil conductivity in one direction at least. I wonder if the problem is related to too high a Brewster angle for vertically polarized signals in your locality.

You're right, NVIS could be achieved with a long (high) vertical. In fact, if you made one just a wavelength long you could cancel the low angle pretty well.

Dave.     
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« Reply #61 on: June 03, 2011, 04:07:18 PM »

Dave, the 40-43' has been popular for a long time and was really popularized when the US was given the  full band and 1500W in the late 70's.

Carl, you need to read up on your history.  The US was NOT "given the full band and 1500W in the late 70's".

There was nothing in the regs that even mentioned 1500W back then; the legal limit was 1 KW DC input to the final, and the full 1800-2000 kc/s wasn't given back until sometime in the mid-1980s. 

In 1979, the 1800-2000 kc/s portion was returned to us in the ITU regulations at the WARC conference, but the FCC sat on its hands and did nothing until sometime about 1981 IIRC, after ARRL and others had petitioned to restore that full portion of the band. But we got only 1800-1900 back, because in some obscure localitiy, reportedly in Canada, LORAN had not yet been completely phased out. Eventually we got the full 1800-2000, but almost immediately 1900-2000 was reallocated to Radiolocation on a primary basis, and amateurs were relegated to the status of secondary users. This was allegedly for the purpose of "reaccommodating" the radiolocation beacons as they were displaced by the expansion of the AM broadcast band.  Within weeks, radiolocation beacons began to appear in the band, but it would be years before the first AMBC station (the one in Elizabeth, NJ) appeared in the extended portion. The only thing that saved the amateur band above 1900 was the advent of GPS. As units became more widely available at low cost, and civilian users were given full resolution down to a few feet, the beacons one by one disappeared from the amateur band, although technically we are still secondary users of 1900-2000.

But even with 1800-2000 kc/s the full band has never been restored to amateurs.  Before WWII, for many years the band was 1715-2000, and for a brief period just before Pearl Harbor the allocation was shifted to 1750-2050, but I am not sure if US amateurs ever actually got to use that full 300 kc/s of band before the shut-down.
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« Reply #62 on: June 03, 2011, 04:07:37 PM »

Iíve seen some YouTube vids of some of these guys. The signals were quite good. I can often copy some UK stations on 3615 or 3625 kHz at around 0600Z or so, especially in the winter months.

On the dreaded slopbucket, Iíve worked a ton of 10 and 50W stations out of the UK. Many are using verticals with modest radial systems or doublets at a height of 30 feet or so. Tom/JJ often calls CQ just for those guys. Itís a hoot hearing a pile-up of 10 Watt signals!

Yes, a small lot and low power is a challenge. But more can be done than first thought, if you are willing to work at it.


Quote
If I had to describe a typical British 80m AM station these days, he would probably be using a G5RV with the centre at about 25ft and a DC input of 50W.
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« Reply #63 on: June 03, 2011, 04:21:26 PM »

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You're right, NVIS could be achieved with a long (high) vertical. In fact, if you made one just a wavelength long you could cancel the low angle pretty well.

I'm not sure what you mean here, Dave. It looks like a full wave vertical is all low angle.?


* Full Wave Vertical.jpg (36.28 KB, 572x387 - viewed 975 times.)
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« Reply #64 on: June 03, 2011, 04:44:02 PM »

I have seen a few of those "back gardens" in cities in the UK, so the real estate for a 160m vertical would be pretty limited. But some UK hams do live in the country where there is more room. Rob, K5UJ describes his place in the Chicago area as pretty much the same, yet I have heard him put out quite a dominating signal on 160m as well as 75. The best strategy would be to lay as many short radials as you can afford the wire for, and make them as long as space permits, and use some kind of top loading on the vertical. A little fire in the wire wouldn't hurt, either (antennas by Eimac  Wink).

According to a source to remain unnamed, some of the "10-watt" top band stations in the UK are actually using retired tube type AM broadcast transmitters running as much as a KW carrier output. If true, I'm not sure where the transmitters came from, because I don't think there ever were a lot of independent 1KW size AM broadcasters in UK or elsewhere in western Europe for that matter, and the cost would be prohibitive to have one shipped from the US or from Canada.

Bud, as I recall, the chart that I saw showed the full wave vertical with the main lobe at a somewhat higher angle, with another very low angle secondary lobe that was a lot weaker. I have it here somewhere in one of my radio books. That low angle lobe might be enough to allow the antenna to work for DX.
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« Reply #65 on: June 03, 2011, 05:29:40 PM »

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Completely untrue. In the past 73, CQ and Radio and other rags had technical articles - often superior to those of QST. The west coast handbook was better than the ARRL handbook too.

Completely true, we are discussing current publishing, not ancient history and besides you forgot HRM.
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« Reply #66 on: June 03, 2011, 05:52:19 PM »

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Iím very sceptical about this 4-square arrangement, Carl, because with only 43ft verticals and 1/8 wavelength spacing on 160m the array gain would probably be offset by the increased loss in each vertical compared to one vertical with no interaction. It will obviously help on receive because of the directivity, but there are easier ways of getting directivity for receive only. If you get very little increase in transmit gain, it seems hardly worth going to all the effort of a 4-square array unless you already use it on 80m. Anyway, it has no bearing on Garyís predicament, so we ought not to be discussing it on this thread, interesting though it may be.

Skeptical you may be but John has made it perform very well as a dual band array. The 1/8 wave spacing offers about the highest gain but mutuals are very hard to control with a full 1/4 wave element. With the losses of the short element it becomes possible and with noticable gain.

Quote
Carl, you need to read up on your history.  The US was NOT "given the full band and 1500W in the late 70's".

Don Im not going to quibble over a few years; WARC, 160 band privileges and 1500W all happened very close together. I dont keep stcky notes on my monitor for trivia Grin

The fishing beacons are still operating down in the low end, I hear them often around 1820-1830 peaking SE from here.

Carl


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« Reply #67 on: June 03, 2011, 10:57:46 PM »

<<Rob, K5UJ describes his place in the Chicago area as pretty much the same, yet I have heard him put out quite a dominating signal on 160m as well as 75.>>

Tnx Don; coming from you I feel like the 101 radials (because I had to have over 100) were not a waste of time and copper!

Rob
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« Reply #68 on: June 03, 2011, 11:08:18 PM »


Don Im not going to quibble over a few years; WARC, 160 band privileges and 1500W all happened very close together. I dont keep stcky notes on my monitor for trivia Grin

The fishing beacons are still operating down in the low end, I hear them often around 1820-1830 peaking SE from here.

One of the things that kind of irks me is the number of newbies who think the 1500w bullsh!t has always been the standard.  And most of the fishing beacons down at the low end (illegal, since the shared portion of the band is 1900-2000 and doesn't include 1820-30) are so PW that they don't bother me. Like the bootleg CBers on 10m, I suggest we just turn up the wick and blast them to oblivion.
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« Reply #69 on: June 04, 2011, 07:24:44 AM »

Bud, youíve got to remember that Iím not good enough to be an engineer, and thatís why I became a scientist! My response about the one-wavelength vertical was an idle answer to a casual question and I was just thinking of canceling radiation at zero degrees and the two opposing half-wave current sections in a full-wave end-fed vertical will do that. If you want to nit pick, my comment about NVIS is not that accurate, either, because no vertical, no matter how long, will produce anything going straight up. Nor is a 32 degree main lobe that low an angle of launch, either. How low is low? I donít think we want to get into debating that!

Carl, Iím not convinced by claims that something works ďvery wellĒ and would have to ask how bad it has to work before itís considered to just work well? There is also no way of knowing how much Johnís location influences his results, either.

Don, the power limit in the UK is now 400 watts output from 1810 to 1850 kHz, and above 1850 kHz itís 15dBW (32 watts PEP). In the old days there were always DX fanatics who ran illegal power, but many of us stuck to 10 watts, or under, just for the challenge of it. We knew who the cheats were, and I could give you their call signs, but wonít for fear of legal action!  Even with the increased power limit these days, there are those who run 1500 watts output on SSB and CW at the low end of 160m because thatís what they can get out of their commercial amplifiers. Iíve even heard them up on the high end running high power sometimes Ė they donít appear to know that there is a lower limit up there and what theyíre doing is that much more obvious! I imagine they donít care. Whoís going to take them to task? OFCOM (our FCC) certainly arenít going to do it.  They donít have the manpower to do anything anymore.

There are still many 160m AM stations running 10 watts, or less, DC input in the UK and they quite happily chat locally with very modest antenna systems. Those who put a bit more effort into improving their antennas do better and work further a field. The most common PA tube in use on 160m AM is the 6BW6 (electrical equivalent of the 6CM6) and you would be hard pressed to run more than 12 watts input to one of them. If you did, the modulator would not provide enough audio to modulate it fully anyway. Thereís still a lot of fun to be had with low power AM on 160m, though in the States it would be more difficult because of interference from high-power stations.
The high-power boys very rarely come above 1850 kHz, so we donít have too much trouble form them. Iím sure plenty of the SSB stations above 1850 kHz are running 100 watts out rather than 32 watts PEP, but we donít generally get a lot of trouble from them. Our main source of interference is USB from Irish, Dutch and Danish trawler men.

Dave.
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« Reply #70 on: June 04, 2011, 02:23:17 PM »

Dave,  what is the ground conductivity like in the UK?  It is okay at my location, not great but not bad either, but in some parts of the US it is nonexistent.

Rob
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« Reply #71 on: June 04, 2011, 03:17:58 PM »

Rob,

Generally, the soil conductivity is not bad in England. There are large parts of the country where the soil conductivity is 10 to 15, or even 10 to 20 mS, such as the Midlands, around Cambridgeshire and Lincolnshire. Other parts are between 4 and 10 mS, whereas Cornwall and Devon are down below 3 mS. Large parts of Northern Scotland are also below 3 mS. In Wales there is a reasonable coastal strip in the south where it's 5 to 10 mS. but for the rest of Wales, it's poor at either below 5, or in some parts below 3 mS.

Where I live in the bulge on the eastern side of the country, it's 5 to 10 mS, so not too bad and not too good, either.

There is a map of the conductivity around the country, produced by the BBC, but I'm not sure if anyone has reproduced it on the web. If we wait long enough, Steve may come up and tell us where to find it.

Dave.
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« Reply #72 on: June 04, 2011, 03:48:30 PM »

Rob,

I've just found a ground conductivity map for the whole world, which appears to be from a CCIR document. You can download it from HAMWAVES at

http://hamwaves.com/antennas/gnd-sigma/vlf_mf_ground_conductivity_atlas.pdf

Dave.
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« Reply #73 on: June 04, 2011, 03:53:41 PM »

Don,

That's very odd about the half-wave vertical on 80m. You'd expect it to go great guns on 80m. I wonder what the ground conductivity is like around your property. You mentioned in a previous posting that you got better results 50 miles away on sky wave than you did on ground wave, which considering your power points to quite poor soil conductivity in one direction at least.

Dave.     

Looks like we're at least 4 but less than 8 millimhos per metre. I am close to a border area, and I doubt that it suddenly jumps from 4 to 8 precisely on the line shown on the map. The figures must be average values calculated over the entireties of the areas shown.

http://filebay1.home.comcast.net/~filebay1/ground.jpg
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« Reply #74 on: June 04, 2011, 04:04:51 PM »

Hello Don.

I was just looking at the ground conductivity map of the US on the FCC site and wondering if you were in the 2mS/m part of TN. I don't exactly know which part of the State you're in, but it's obviously not that part in the east where it's really bad.

I don't know how they gather the data for these maps, or whether they average the figures out over the year, or not. The figures must depend on the moisture content of the soil, so it would be interesting to know how they deal with that. Perhaps the CCIR document mentions it somewhere. I'll have to read it in full.

Dave.
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Dave,G3UUR
Vintage AM from the East of England
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