Re: [Elecraft] Two Band Moxon/wire beam
Okay, found it - WA1X's technique for tuning a Moxon rectangle: http://lists.contesting.com/archives//html/Towertalk/2005-03/msg00852.html My apologies for not finding it sooner. 73, VR2BrettGraham ___ Elecraft mailing list Post to: Elecraft@mailman.qth.net You must be a subscriber to post to the list. Subscriber Info (Addr. Change, sub, unsub etc.): http://mailman.qth.net/mailman/listinfo/elecraft Help: http://mailman.qth.net/subscribers.htm Elecraft web page: http://www.elecraft.com
Re: [Elecraft] Two Band Moxon/wire beam
Gil, It performed well during our special event this weekend. We had it up at an average height of 25'. We used it on both 20 and 40 meters simultaneously using Array Solutions RF filters with a little 2nd harmonics or phase noise on 20 from the 40 meter transmitter. We were able to reduce this interference about 18 dB using a shorted coax stub on the 40 meter feed line. The resonant frequency is 3 to 5% low from the design value, which turn out to be caused by my not taking into account the velocity factor of the insulated wire I used for elements. Hopefully, we will get everything corrected for field day. Chas, W1CG At 09:38 AM 10/3/2005, Gil Stacy wrote: Hi Charles, The trimming technique of W1AX looks like a well-thought out approach to solving the idiosyncracies of location diffferences in erecting the antenna. I've always been impressed by the Moxon technology in using wire to erect a simple gain antenna. I emailed W1ZY about his switchable 40 meter Moxon and never heard back. The sound file of his front and back switching is very impressive. I suppose he had a lot of cutting and trying to perfect it as well as more relays than one can imagine. Let us all know how your antenna performs. 73, Gil NN4CW ___ Elecraft mailing list Post to: Elecraft@mailman.qth.net You must be a subscriber to post to the list. Subscriber Info (Addr. Change, sub, unsub etc.): http://mailman.qth.net/mailman/listinfo/elecraft Help: http://mailman.qth.net/subscribers.htm Elecraft web page: http://www.elecraft.com
Re: [Elecraft] Two Band Moxon/wire beam
W1CG replied: one big snip Presumably you know the dielectric constant of that insulation, verified that the wire you have is in the same neighborhood done all your modelling based on that figure? I have previously assumed that any wire insulated or not, in space, has the same velocity factor as bare wire. Why wouldn't it? I can see that a twisted pair, or feed line would be affected by velocity factor. Because, quite simply, it does. You are not above the laws of RF black magic - never were never will be, full stop. Shorten things by 2-3% - perhaps more - in your model see what happens. That is what happens when you use insulated wire without taking into consideration the effect of the insulation. On 40m somewhere around about a quarter-wave above ground - without any consideration for the insulation - IMHO nothing will be where you expect it to be. It never is for me. snip again Remind me what WA1X's approach is again. Tune elements such that they are resonant reasonably close to where they need to be - both driver reflector. In a nutshell, not really possible to make a Moxon without a bit of tweaking. Mine - made of wire that has very little dielectric in contact with it (just the end insulators) - required quite a bit of trimming before it showed reasonable match _and_ performance based on pattern. Remember, this was a 10m Moxon at a height of wavelengths greater than yours above ground. Get higher up things should change, but I really believe you are taking a hit from these two very significant factors (with ground _so_ close that it might be greater than the insulation). Compare against another antenna I suspect you will see - as I did. As for simultaneous operation, other than harmonics spurs, the other concern is phase noise K2 is quite good in that department. Harmonics usually are more of a problem on CW due to relationship of bands (less so in ITU R2, where 2 x 40m SSB band is mostly above 14.35 Mc). But as this all has to do with evil competitive operation judging from lack of interest from the list, best to terminate this discussion. GL. 73, VR2BrettGraham ___ Elecraft mailing list Post to: Elecraft@mailman.qth.net You must be a subscriber to post to the list. Subscriber Info (Addr. Change, sub, unsub etc.): http://mailman.qth.net/mailman/listinfo/elecraft Help: http://mailman.qth.net/subscribers.htm Elecraft web page: http://www.elecraft.com
Re: [Elecraft] Two Band Moxon/wire beam
Brett, Tnx for the comments. Tried the antenna today and successfully operated simultaneously with both transceivers on the phone bands. There was some second harmonic noise of the 40 meter transmitter on 20 when an ICOM 746 Pro was used at 100 watts; none when a K2 at 10 watts was used. The noise was about S5 and could be easily tuned out as it It was on certain rather narrow frequencies. Voltage on 20 meters coming through the filter was 55 uv, 0 to peak, measured with a scope when the ICOM was transmitting. No noise at all on 40 meters when the 20 meter transmitter was transmitting. Voltage on the line after the 40 meter filter was 7 uv, 0 to peak. The antenna seems to have good gain. Worked a bunch of 6's in the CA QSO contest as well as some stations in IO and MO on 20. On 40, contacts ranged from E. PA to Pittsburgh and other states, VA to Ont. with similar distances from RI. Signal reports were good. Antenna is pointed West. Terrain flat, farmland, about 50 feet ASL. See below for other comments. Chas, W1CG At 08:07 PM 9/30/2005, VR2BrettGraham wrote: W1CG continued: To answer your question, I am using stranded, silver plated, teflon insulated #16 wire. It is plenty strong. I have a 3/16 Dacron line between the two poles to take the strain off the wires. This also decreases the vertical bend and completely eliminates the horizontal bend of the two poles. Presumably you know the dielectric constant of that insulation, verified that the wire you have is in the same neighborhood done all your modelling based on that figure? I have previously assumed that any wire insulated or not, in space, has the same velocity factor as bare wire. Why wouldn't it? I can see that a twisted pair, or feed line would be affected by velocity factor. If so, then you can see how ground dominates if not, then between both ground insulation your elements are nowhere near where you think they are. I don't understand what you mean. (To review, the antenna is a 40 meter Moxon wire beam with a 2 element 20 wire meter beam inside. There are two supports, 22' long fiberglass poles at each end, spaced 45 '. There are two feed lines.) We put the antenna up today for our annual special event at for the Harvest Faire at the Norman Bird Sanctuary in Middletown, RI for this weekend. Listen for us on 20 and 40. Call is W1SYE, Newport County Radio Club. (See Sept QST, special events). The antenna is about 30' high on one end and about 25' on the other, from a portable mast to a tree. The Fo and Zo is not much different from what it was at 21'. Fo is about 14.00/7.00 MHZ . SWR is 1:1, 50 ohms on both bands per MFJ 159B. 2:1 band width is (top frequency) 14.4 MHz and 7.25 MHz resp. I still want to move it up to 14.2 and 7.25 MHz. It's a very nice beam; doesn't sag much and it is easy to erect. The weight is about 18# which includes everything supported. Not many 2-element 40m beams that can be robust only weigh that much - not to mention less wingspan far better F/R than a yagi. The feed lines are two lengths of double shielded RG-58 (TRF-58). I am going to try simultaneous operation on 40 and 20 using 20 and 40 meter bandpass filters by Array Solutions. The 40M filter has an insertion loss of 70 dB on 14 MHz and the 20M filter has an insertion loss of 35 dB on 7 MHz. I will use my K2/100 with a LDG Z-11 tuner and the club's Ten Tec Jupiter with its LDG tuner. I will try my other K2 with KAT2 in case the Jupiter overloads on receive. I don't know how this will work out. Calculations say it won't work at 100 watts as there is not enough attenuation, but I will try it and report results. There must be some power level of the transmitters that will work. It would be handy for field day, but if it doesn't work we will just have to put the second transceiver on 80 meters using another antenna. Or else use separate receiving antennas. The K2 with the KAT2 can do this; I don't know about a K2/100 with a KAT100. Maybe someone can enlighten me. With two 400 watt rigs into two bands of a tribander simultaneously, those filters will work - though without stubs the 2nd harmonic of the 40m station will render some number of dozens of kilocycles on the higher band useless. I want to add a stub or stubs. I am thinking of a 1/4 wave 40 meter shorted stub, on the 40 meter feed line. Where is the best place to put it? (at transmitter before filter, after filter, or at antenna). I will try it tomorrow and can easily try it at all three locations. How about stubs on the 20 meter feed line? Be sure to decouple the feeders at the feedpoints, too. Look at how each driver looks as you connect, disconnect or short the far end of the feeder to the other driver. I did that and there is no change from open to 50 ohms to shorted. I would imagine that your antenna probably has the two bands' drivers electrically closer therefore you will have far
Re: [Elecraft] Two Band Moxon/wire beam
W1CG continued: To answer your question, I am using stranded, silver plated, teflon insulated #16 wire. It is plenty strong. I have a 3/16 Dacron line between the two poles to take the strain off the wires. This also decreases the vertical bend and completely eliminates the horizontal bend of the two poles. Presumably you know the dielectric constant of that insulation, verified that the wire you have is in the same neighborhood done all your modelling based on that figure? If so, then you can see how ground dominates if not, then between both ground insulation your elements are nowhere near where you think they are. (To review, the antenna is a 40 meter Moxon wire beam with a 2 element 20 wire meter beam inside. There are two supports, 22' long fiberglass poles at each end, spaced 45 '. There are two feed lines.) We put the antenna up today for our annual special event at for the Harvest Faire at the Norman Bird Sanctuary in Middletown, RI for this weekend. Listen for us on 20 and 40. Call is W1SYE, Newport County Radio Club. (See Sept QST, special events). The antenna is about 30' high on one end and about 25' on the other, from a portable mast to a tree. The Fo and Zo is not much different from what it was at 21'. Fo is about 14.00/7.00 MHZ . SWR is 1:1, 50 ohms on both bands per MFJ 159B. 2:1 band width is (top frequency) 14.4 MHz and 7.25 MHz resp. I still want to move it up to 14.2 and 7.25 MHz. It's a very nice beam; doesn't sag much and it is easy to erect. The weight is about 18# which includes everything supported. Not many 2-element 40m beams that can be robust only weigh that much - not to mention less wingspan far better F/R than a yagi. The feed lines are two lengths of double shielded RG-58 (TRF-58). I am going to try simultaneous operation on 40 and 20 using 20 and 40 meter bandpass filters by Array Solutions. The 40M filter has an insertion loss of 70 dB on 14 MHz and the 20M filter has an insertion loss of 35 dB on 7 MHz. I will use my K2/100 with a LDG Z-11 tuner and the club's Ten Tec Jupiter with its LDG tuner. I will try my other K2 with KAT2 in case the Jupiter overloads on receive. I don't know how this will work out. Calculations say it won't work at 100 watts as there is not enough attenuation, but I will try it and report results. There must be some power level of the transmitters that will work. It would be handy for field day, but if it doesn't work we will just have to put the second transceiver on 80 meters using another antenna. Or else use separate receiving antennas. The K2 with the KAT2 can do this; I don't know about a K2/100 with a KAT100. Maybe someone can enlighten me. With two 400 watt rigs into two bands of a tribander simultaneously, those filters will work - though without stubs the 2nd harmonic of the 40m station will render some number of dozens of kilocycles on the higher band useless. Be sure to decouple the feeders at the feedpoints, too. Look at how each driver looks as you connect, disconnect or short the far end of the feeder to the other driver. I would imagine that your antenna probably has the two bands' drivers electrically closer therefore you will have far greater interaction between the two bands than on my tribander. Hairpins seem to work pretty good on that, but that means more trimming. Anyway, I think the key point is the wire like I said about my bare wire Moxon, there's a bit of mucking about in practice to get it to work. I would not make another Moxon unless I'm exactly duplicating something else (right down to the wire) - otherwise both elements need trimming WA1X's approach (I think it was) is probably the best way to go about it. Enjoy! 73, VR2BrettGraham ___ Elecraft mailing list Post to: Elecraft@mailman.qth.net You must be a subscriber to post to the list. Subscriber Info (Addr. Change, sub, unsub etc.): http://mailman.qth.net/mailman/listinfo/elecraft Help: http://mailman.qth.net/subscribers.htm Elecraft web page: http://www.elecraft.com
Re: [Elecraft] Two Band Moxon/wire beam
Brett, To answer your question, I am using stranded, silver plated, teflon insulated #16 wire. It is plenty strong. I have a 3/16 Dacron line between the two poles to take the strain off the wires. This also decreases the vertical bend and completely eliminates the horizontal bend of the two poles. (To review, the antenna is a 40 meter Moxon wire beam with a 2 element 20 wire meter beam inside. There are two supports, 22' long fiberglass poles at each end, spaced 45 '. There are two feed lines.) We put the antenna up today for our annual special event at for the Harvest Faire at the Norman Bird Sanctuary in Middletown, RI for this weekend. Listen for us on 20 and 40. Call is W1SYE, Newport County Radio Club. (See Sept QST, special events). The antenna is about 30' high on one end and about 25' on the other, from a portable mast to a tree. The Fo and Zo is not much different from what it was at 21'. Fo is about 14.00/7.00 MHZ . SWR is 1:1, 50 ohms on both bands per MFJ 159B. 2:1 band width is (top frequency) 14.4 MHz and 7.25 MHz resp. I still want to move it up to 14.2 and 7.25 MHz. It's a very nice beam; doesn't sag much and it is easy to erect. The weight is about 18# which includes everything supported. The feed lines are two lengths of double shielded RG-58 (TRF-58). I am going to try simultaneous operation on 40 and 20 using 20 and 40 meter bandpass filters by Array Solutions. The 40M filter has an insertion loss of 70 dB on 14 MHz and the 20M filter has an insertion loss of 35 dB on 7 MHz. I will use my K2/100 with a LDG Z-11 tuner and the club's Ten Tec Jupiter with its LDG tuner. I will try my other K2 with KAT2 in case the Jupiter overloads on receive. I don't know how this will work out. Calculations say it won't work at 100 watts as there is not enough attenuation, but I will try it and report results. There must be some power level of the transmitters that will work. It would be handy for field day, but if it doesn't work we will just have to put the second transceiver on 80 meters using another antenna. Or else use separate receiving antennas. The K2 with the KAT2 can do this; I don't know about a K2/100 with a KAT100. Maybe someone can enlighten me. Chas, W1CG At 06:23 PM 9/29/2005, VR2BrettGraham wrote: W1CG replied to K5KVH: Thank you for the insight. I calculated the % the wire lengths were off by % the frequency was off, and I also moved the model up in frequency (by shortening wire lengths in the model) by the amount it differed from the measurement. In other words, the actual was about 200 KHz below the model, so I moved the model up 200 KHz. The model was at the same height as the measurements. Both techniques produced results that were close. One thing I found was to not change the wire spacing at the ends, but just to change the length of wires between the main supports. I will wait until we hoist it to the final height which I estimate to be near 30' and take some more measurements then trim based on that. I think we can operate with the existing lengths as the top band edge is within the 2:1 SWR bandwidth at 21'; it may be a little off at 30' as the resonant frequency goes down as the height is increased, but we don't have to operate near the top end of the band. We have a LDG tuner, so it should be able to tune ok. I don't recall if you mentioned if you were using bare or insulated wire. Between the several percent that contributes the coupling between the elements, I think WA1X's (I believe it was) suggestion on towertalk or somewhere a while back on how he trims Moxons is the way to go. With bare wire, I have done quite a bit of mucking around trying to tune a 10m Moxon with effect of ground (reinforced concrete roof top) a half wavelength up. A decent match with reasonable pattern I believe is probably much easier to achieve by tuning each element separately as WA1X described. The coupling in a Moxon rectangle is pretty intense - it is a good idea to maintain geometry after trimming the ends, though some sort of directivity will remain if you don't (up to a point). I have done all sorts of models of Moxons all multi-band approaches other than back-to-back look to be hard to achieve in practice (nesting, mix with yagi elements, sleeves, etc). Nested Moxon reflector for the higher band sleeve around low band driver looks awfully interesting, but would require a _lot_ of work to trim into submission in the real world. GL. 73, VR2BrettGraham ___ Elecraft mailing list Post to: Elecraft@mailman.qth.net You must be a subscriber to post to the list. Subscriber Info (Addr. Change, sub, unsub etc.): http://mailman.qth.net/mailman/listinfo/elecraft Help: http://mailman.qth.net/subscribers.htm Elecraft web page: http://www.elecraft.com
Re: [Elecraft] Two Band Moxon/wire beam
Stuart Thank you for the insight. I calculated the % the wire lengths were off by % the frequency was off, and I also moved the model up in frequency (by shortening wire lengths in the model) by the amount it differed from the measurement. In other words, the actual was about 200 KHz below the model, so I moved the model up 200 KHz. The model was at the same height as the measurements. Both techniques produced results that were close. One thing I found was to not change the wire spacing at the ends, but just to change the length of wires between the main supports. I will wait until we hoist it to the final height which I estimate to be near 30' and take some more measurements then trim based on that. I think we can operate with the existing lengths as the top band edge is within the 2:1 SWR bandwidth at 21'; it may be a little off at 30' as the resonant frequency goes down as the height is increased, but we don't have to operate near the top end of the band. We have a LDG tuner, so it should be able to tune ok. A comment on the vertical pattern. For field day and special events the high angle of elevation of radiation on 40 meters you get at a height of 30' is not a disadvantage as we are looking for local contacts instead of DX. About 90% of the US is in the horizontal beamwidth from RI. Just northern New England and southern Florida is out side the 3 dB beamwidth. It used to bother me that with a dipole 1/2 of the radiated power was going toward Europe, which really doesn't participate in field day. Chas, W1CG At 05:06 PM 9/26/2005, Stuart Rohre wrote: Charles, With dual band close spaced beams, everything interacts. You can try adjusting the wire lengths by the percentage you were off your target frequency, or just operate them as they fell. They will vary with height, and there is no compelling need to have them exactly resonant in cases like this, as long as your are getting about the beam action you want. Your SWR actual at 21 feet seem to be OK for operations. Or just use a tuner to touch up the match. Stuart K5KVH ___ Elecraft mailing list Post to: Elecraft@mailman.qth.net You must be a subscriber to post to the list. Subscriber Info (Addr. Change, sub, unsub etc.): http://mailman.qth.net/mailman/listinfo/elecraft Help: http://mailman.qth.net/subscribers.htm Elecraft web page: http://www.elecraft.com
Re: [Elecraft] Two Band Moxon/wire beam
Charles, With dual band close spaced beams, everything interacts. You can try adjusting the wire lengths by the percentage you were off your target frequency, or just operate them as they fell. They will vary with height, and there is no compelling need to have them exactly resonant in cases like this, as long as your are getting about the beam action you want. Your SWR actual at 21 feet seem to be OK for operations. Or just use a tuner to touch up the match. Stuart K5KVH ___ Elecraft mailing list Post to: Elecraft@mailman.qth.net You must be a subscriber to post to the list. Subscriber Info (Addr. Change, sub, unsub etc.): http://mailman.qth.net/mailman/listinfo/elecraft Help: http://mailman.qth.net/subscribers.htm Elecraft web page: http://www.elecraft.com
[Elecraft] Two Band Moxon/wire beam
Hi, I need some advice on a wire beam I built for field day and special events. It has two fiberglass poles 22' long spaced 45' with a wire Moxon for 40 M on the outside and a two element 20 meter beam between the 40 meter Moxon. It has there is little interaction between the beams either by model of by measurement. It is fed with two lengths of RG-58 through 1:1 baluns at the antenna. I designed it using EZNEC, and optimized it for gain with an eye on F/B ratio and impedance. A few days ago I hosted it to 21' for a test. The design was for 30' which will be the actual height in operation. I have a chance to trim it before moving it to the special event location and hoisting it to 30'. Measurement vs EZNEC values for Fo and Zo are as follows at 21' and 30'. Fo model: 7.26 MHz at 21', 7.19 MHz at 30' Zo model: 41.85 Ohms at 21', 35.6 Ohms at 30' Fo actual: 6.93 MHz, at 21' Zo actual: 50 Ohms, at 21' Fo model: 14.2 MHz at 21', 14.235 at 30' Zo model: 35.2 Ohms at 21', 50 ohms at 30' Fo actual: 13.99 MHz at 21' Zo actual: 65 Ohms. at 21' My question is, should I reduce the length of all wires in each beam the % that the frequency is off in each beam and leave the spacing alone, or should I reduce everything? It seems the frequency is off because the model doesn't take into account all of the end effects, but the spacing is not subject to end effects and should be left alone. I have no way to measure accurately measure the elevation angle, gain and F/B ratio. The .ez files are available for the asking to individuals. Tnx for your time. Chs, W1CG ___ Elecraft mailing list Post to: Elecraft@mailman.qth.net You must be a subscriber to post to the list. Subscriber Info (Addr. Change, sub, unsub etc.): http://mailman.qth.net/mailman/listinfo/elecraft Help: http://mailman.qth.net/subscribers.htm Elecraft web page: http://www.elecraft.com
