++++++++++++++++++++++++++++++++ Date: Tue, 22 May 2001 21:16:25 -0500 From: "Andy Anderson" Subject: Re: [Elecraft] Superantennas MP-1 Julian, I have the PW-1 on the same tripod, but my experience has been very different. I live in Texas, and the area where my home is consists of clay not far below the soil. I believe there is bedrock down not too far. Anyway, I have tried a variety of things I'd like to share with you. First, I used a AEA CIA-HF to do the SWR/X/C/etc readings with, using 50 feet of RG-8X as feeder from the K1 (#636), the FT-817, and the TS-850S. On 40m I get 1.2:1 (centered on 7.040 Mc) as the best reading on damp soil; on 20m (centered on 14.060Mc) I measure 1.3:1 -- or sometimes 1.22:1 at best -- depending on soil dampness. On 30m, I found there is too little adjustment to make a separate mark on the coil, so I get about 1.5:1 on 30m (centered on 10.106 Mc). The very best I can get on other bands is 1.8:1, but sometimes 2.5-3.0:1 is the best I get. Still not bad, and both the KAT1 and the Z-11 tune it very handily. It seems like to me I got 3.0:1 or so on 80m with the extra coil installed, but I don't remember. An interesting thing happened when I took the K1 and CIA to Texas Star Party in Ft. Davis (West) Texas last week. I set the PW-1 up behind the bunkhouses on hard clay and rocks. It was very dry, at least at the surface, and Prude ranch sits in a valley surrounded on all sides by mountains. The signal to the East, NE, and SE was completely blocked by the bunkhouses. To my surprise, I go 1.0:1 on 20m, which was very active one of the days I listened, and 1.1:1 on 40m...both better than here at the house. I was easily able to pick put stations in California (lots of W/K6's), Oregon-Washington, and even Colorado. Picked a few K0/N0s while I was listening, but as should be expected, the -6 area was most active for what I was receiving. The thing that really blew me away abou this was the rocky-clay soil had better characteristics -- even in a valley -- than I got here at the house. It was a pleasant surprise. Sometime back, I spoke to Vern about not being able to get below about 2.4:1 on a lot of the bands, and he was surprised, but soil obviously has a large effect on the results. One of the experiments I've wanted to do, but have not done yet, is to 1) put 10' sections of aluminum foil (Reynolds Wrap here) under the radials, and maybe the whole ground under the antenna, and 2) do the same with the old metal (aluminum or whatever) door screening that is used to keep out bugs. If anyone has already done this, I'd be interested in the results. Another thing I'd like to try is tap the base on all the sides and add more radials, or maybe just make up a fairly dense "star" pattern of 10 foot radials that I can add to the ones Vern ships. That way, these (radials) could be rubber banded together and stay in the tube with the rest of the antenna during travel. Speaking of tubes, I found a need carrier for the PW-1, and you MP-1 guys may want to look at them too. If you have a Container Store in your area, they sell collapsible, adjustable black tubes for about $10/each that are perfect for protecting your Super Antenna. The come with a web shoulder strap, and I've found it very convenient. 73, Andy W5VCJ - ----- Original Message ----- From: "Julian" To: "Elecraft List" Sent: Tuesday, May 22, 2001 4:51 AM Subject: [Elecraft] Superantennas MP-1 > Some months ago, I bought an MP-1 antenna with tripod for portable use. I > haven't made much use of it because of winter weather and then > foot-and-mouth restrictions, but I have experimented with it from home and > from the car. Although the antenna would peak up on each band I usually > could not obtain a low SWR. > > Since getting the KBT2 option in my K2 it has become apparent that in my > experiments, the antenna was seeing a ground through the radio itself. On > the lower bands (20m and down) this was clearly a better ground than that > provided by the four 10' radials supplied. With the K2 powered by its > battery and connected to nothing other than the feeder to the antenna, the > SWR anywhere near the point of maximum received signal can be 4 or 5 to 1, > and usually fluctutates. Putting my hand on or near the feeder or the radio +++++++++++++++++++++++++++++++++++++++ Date: Wed, 23 May 2001 20:24:06 -0700 From: "Ron D' Eau Claire" Subject: RE: [Elecraft] Superantennas MP-1 Julian wrote: To > my surprise, I go 1.0:1 on 20m, which was very active one of the days I > listened, and 1.1:1 on 40m...both better than here at the house. I was > easily able to pick put stations in California (lots of W/K6's), > Oregon-Washington, and even Colorado. Picked a few K0/N0s while I was > listening, but as should be expected, the -6 area was most active > for what I > was receiving. > > The thing that really blew me away abou this was the > rocky-clay soil had > better characteristics -- even in a valley -- than I got here at > the house. Better 'characteristics' for a low SWR perhaps, but the worse the ground and the poorer the radiation efficiency of the antenna system, the easier you should expect your ATU to find a match under most conditions. You should expect to find the tuning a lot less 'finicky' since you are pumping most of the r-f into a very broadband resistor (the poor earth) instead of a higher-Q radiator (the whip). Perhaps a better measure would be the bandwidth of the system. If the short antenna exhibits a very narrow frequency range over which the SWR will be reasonable without the KAT2 retuning, that would be a very good sign that the system efficiency is high. In an efficient system, a short radiator will have less bandwidth, and the bandwidth will drop very fast as the physical length of the radiator drops below 1/4 wavelength. If it doesn't, you have a resistive loss in there somewhere. It might be a lossy earth connection, a lossy loading coil or some other resistor that consumes a good part of the r-f instead of letting it be radiated. Ron AC7AC K2 # 1289 ++++++++++++++++++++++++++++++++++++++++ Date: Tue, 22 May 2001 23:07:40 -0500 From: Robert Perkins Subject: Re: [Elecraft] Superantennas MP-1 I've got the little one, I can't remember which model number is which. I got a decent match on 40, each higher band was worse. I don't really understand why the short radials had the best swr on 40. At about the same time I read a post on one of the reflectors commenting that mobile antennas worked as well as they do because of capacitance to ground. I also recalled an article in QST a year or so ago where strips were used like an Outbacker tripod. So I noted that the last bit of really violent weather that claimed part of my roof also donated a piece of what Texans call tin roof. It must have come from several miles away, nobody around here has a barn like that. The proper name for this stuff is probably corrugated iron. It's galvanized, which as I recall is less conductive than copper, but better than tarnished copper or aluminum. The antenna is still sensative to ground moisture level, and I had to weight it down or mow under it more often. The grass had lifted it almost 4". Weights were easy :) My piece of tin is only about 1' by 4.5' and it made a marked difference. I went to the local building supply place looking for the sheet metal strips that roofers use, I found aluminum in rolls one foot by 50'. I had decided to look around for galvanized iron, but I'd expect the difference would not be measurable. I envision four strips as long as can be rolled up easily for transport. I also bought a HyGain mobile mast, the 5 footer. I don't intend to pack the HyGain part in luggage or a backpack, and adjustments at shoulder level are much handier. I hope the longer mast improved performance but I don't have the equipment to prove it. At 09:16 PM 5/22/2001 -0500, Andy Anderson wrote: >Julian, > > I have the PW-1 on the same tripod, but my experience has been very ------ (Snipped)------------ +++++++++++++++++++++++++++++++++++ Date: Wed, 23 May 2001 10:49:39 -0700 From: Louis Hlousek Subject: Re: [Elecraft] Superantennas MP-1 <>> You can model all these antennas in EZNEC using real ground and you will find the same thing with the models. (It is kind of tedious inputting the model of a the couch spring.) An interesting thing is that short loaded whips outperform 1/4 wave verticals if you neglect the losses in the coil. I should also point out that except for losses in matching networks and feedlines there is no benefit in having the antenna resonant. Luigi W7DZN ++++++++++++++++++++++++++++++++++++++++++ Date: Thu, 24 May 2001 00:32:31 +0000 From: Michael Rioux Subject: RE: [Elecraft] Superantennas MP-1 As one who has operated from many DX locations - AMEN!!! 73 de W1USN - Mike I I >have NEVER found anything that even begins to approach the performance of a >simple resonant dipole. +++++++++++++++++++++++++++++++++ Date: Thu, 24 May 2001 09:48:00 -0100 From: "Julian" Subject: Re: [Elecraft] Superantennas MP-1 Someone who saw my posts on this topic in another forum suggested that I should simply adjust the MP-1 coil for maximum noise or signal in the receiver, which will indicate the point of maximum efficiency and highest Q, and then transmit. Don't worry about the SWR. Obviously, the KAT2 could be used to tune out the SWR. Feeder losses should be small, if the feeder is short. This is nice and simple, and I'd welcome comments on it as a method of operation from those in the know. This still leaves me puzzled as to the effect of the radials and/or counterpoise on overall efficiency, since clearly they do affect things. I'm being told by someone else that ground coupling is a bad thing, especially for QRP operation, because precious power is wasted warming up the earth. This presumably comes from looking at the MP-1/counterpoise combo as a wacky vertical dipole with half of it laying on the ground. +++++++++++++++++++++++++++++++++