SOTAwatch2
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Full list of discussion topics| Post by G7CNM on 20th May 2012 at 15:47 |
| Hi,All. Would apreciate some advice,getting myself kitted out for the good wx we will be having soon?? Would like to try some activations using 4m fm and have ordered a woxun 4&2m handheld.Im going to try using a simple 4m wire dipole that Ive made on the basis it can be easily carried and taped verticle to a 5m fibreglass fishing pole.Do you think this will work ok or could I do better?Im an enthusiastic 4m fan and know it can be quiet out there but also rewards effort.Any suggestions? Dave. G7CNM |
| Post by G4BLH on 20th May 2012 at 15:57 |
| In reply to G7CNM: A lot of 4m activators use this J-pole http://www.summits.org.uk/tiki-index.php?page=4m+J-pole or something similar. Regards, Mike G4BLH |
| Post by G7CNM on 20th May 2012 at 18:59 |
| In reply to G4BLH: Thanks Mike will have to make one and give it a go. Regards, Dave G7CNM. |
| Post by G3NYY on 21st May 2012 at 10:37 |
| In reply to G7CNM: Yes, I have been using this j-pole for the past 18 months and find it very good ... a bit better than a vertical dipole. Good luck! 73, Walt (G3NYY) |
| Post by G8XYJ on 21st May 2012 at 10:47 |
| In reply to G7CNM: Hi Dave It's great to hear that another Radio Amateur is keen to use this excellent band for SOTA. The design for the slim jim is spot on if you use 300ohm ladder feed. When I made mine using 450ohm ladder feed I added an extra 30cm to the top section to make it work! In addition the fact that it rolls up and fits into a rucksack makes it ideal for SOTA applications. I am pleased to say that at the time of writing I have used this Antenna, a 7 metre fishing pole and the Wouxun (single band 4m radio) on 137 activations and have had a plentiful amount of QSOs. Have fun 73 Matt G8XYJ |
| Post by G7CNM on 21st May 2012 at 19:48 |
| In reply to G8XYJ: Thanks Matt,Walt, Hope to work you on 4m soon looks like wx lmproving at last! All the best 73 Dave G7CNM |
| Post by ON4TA on 22nd May 2012 at 07:42 |
| In reply to G7CNM: I use a J-pole made out of 450 ohm ribbon cable. It can be coiled up and strapped to your rucksack. I fasten it to a 6m fiber pole with reusable tie wraps. It is easy to erect under almost any circumstances. I made a similar antenna for 2m activation. To swap easily I have added +- 30cm section of coax to each antenna with an N-plug and use 5m low loss coax to connect to a 4m/2m handheld, me sitting under the fiber mast. I have made many enjoyable 4m SOTA QSO in G, GW and EI land recently. 73, Phil ON4TA |
| Post by G8ADD on 22nd May 2012 at 10:23 |
| In reply to G3NYY: > Yes, I have been using this j-pole for the past 18 months and find it > very good ... a bit better than a vertical dipole. Hi, Walt, isn't a J-pole a half-wave dipole end fed with a matching section? I was looking at the dimensions to make one for six metres now we are getting some Es openings, but it looks simpler to make a dipole. 73 Brian G8ADD |
| Post by M0CEF on 22nd May 2012 at 12:39 |
| In reply to G8ADD: I would not expect much of a difference in the performace of a J-pole and a vertical dipole, but I think I can see why the former can be preferable for portable operation. If made from flexible material, it rolls up easily (as has already been said), and because the feedline is (mechanically) an extension of the aerial, it hangs straight when suspended from the top end. Not so easily done with a run-of-the-mill dipole. In a pinch, you could also make a vertical dipole from an end of coaxial cable, just by pulling back a sufficient length of the braid. Not exactly waterproof, but any aerial is better than none at all ;-) 73, Jan-Martin |
| Post by K6ILM on 22nd May 2012 at 15:10 |
| In reply to M0CEF: . Yes, the J-pole is only a couple of db better than the dipole, but very easy to construct covering two bands....if you use a mixture of twin lead and RG-174. I watched the inventor of the DBJ-2 make one last month, after which he gave it to me in exchange for 15 USD. I wind it into a 6 inch dia roll and squash that into a narrow oval suitable for slipping into a trouser pocket. Works for 2m and 70cm. Here's his write-up: http://archive.k6ya.org/docs/DBJ2_port_art.pdf Elliott, K6ILM |
| Post by G3NYY on 22nd May 2012 at 16:03 |
| In reply to G8ADD: > Hi, Walt, isn't a J-pole a half-wave dipole end fed with a matching > section? I was looking at the dimensions to make one for six metres > now we are getting some Es openings, but it looks simpler to make a > dipole. Yes, it is. However, feeding a centre-fed vertical dipole with coax is problematic in a portable situation because if the coaxial feed line is allowed to drop down parallel to the lower half of the dipole it will unbalance the antenna and lead to a severe mismatch and loss of gain. Ideally, the feeder needs to run out at 90 degrees to the driven element for at least a half wavelength ... not practicable if you are using a fishing pole to support the vertical radiator. The J-pole, being an end-fed half wave, overcomes this problem quite neatly. You need to insert a balun at the feedpoint. Usually a coaxial choke balun is used, which is just a few turns of the coax feeder wound on a convenient plastic former, or just taped together. Actually, the "Slim Jim" variant is what I use. It relates to the J-pole in the same way that a folded dipole relates to a regular dipole. If correctly matched, the Slim Jim has an extremely low angle of radiation. This has the effect of enhancing the apparent gain of the antenna compared to a simple dipole or 5/8 whip. 73, Walt (G3NYY) |
| Post by G3CWI on 22nd May 2012 at 16:36 |
| In reply to G3NYY: > If correctly matched, the Slim Jim has an extremely > low angle of radiation. Interesting idea. Matching changes the angle of radiation? I don't recall ever seeing that written before. What is the matching condition that gives this low angle of radiation? 73 Richard G3CWI |
| Post by MW0IDX on 22nd May 2012 at 16:56 |
| In reply to G7CNM: I use a slim jim for 2m activations using 300 Ohm ribbon. I have a 6m version using 450 Ohm twin feed high in a tree at home. Both work well. 73 Roger MW0IDX |
| Post by G3NYY on 22nd May 2012 at 18:12 |
| In reply to G3CWI: If it is not correctly matched, it will cease to operate as a Slim Jim and the radiation pattern will be unpredictable. I should have thought that was self-evident. 73, Walt (G3NYY) |
| Post by G3CWI on 22nd May 2012 at 18:30 |
| In reply to G3NYY: ROTFL. Thanks Walt. Priceless. I wonder how my doublet works? 73 Richard G3CWI |
| Post by G8ADD on 22nd May 2012 at 18:49 |
| In reply to G3NYY: Surely in the J-pole or Slim Jim, the feeder hangs down close to or even touching the matching section randomly as the wind takes it and is going to unbalance it making the performance unpredictable? 73 Brian G8ADD |
| Post by G3NYY on 22nd May 2012 at 18:59 |
| In reply to G3CWI: > I wonder how my doublet works? So do I. :-) 73 de G3NYY |
| Post by G7CNM on 22nd May 2012 at 20:21 |
| In reply to all, your comments have been very helpful made me think of a few things I have not considered! Many Thanks. Dave G7CNM. |
| Post by 2E0YYY on 22nd May 2012 at 21:36 |
| In reply to G7CNM: > In reply to all, > your comments have been very helpful made me think of a few things I > have not considered! Looks like I'm going to need some 4m kit, Dave! Thanks for the 2 calls today, fine contacts. 73 Mike 2E0YYY |
| Post by G7LAS on 26th May 2012 at 12:32 |
| In reply to G8XYJ: "It's great to hear that another Radio Amateur is keen to use this excellent band for SOTA. " Not wanting to upset anyone... I understand the attraction of 6m and "below" and 2m and "above," but I've always thought of 4m as having no redeeming features! What *exactly* about 4m makes it "excellent"!??? |
| Post by G3NYY on 26th May 2012 at 13:23 |
| In reply to G7LAS: >What *exactly* about 4m makes it "excellent"!??? Well, in days gone by, it was a "Class B Free Zone". ;-) 73 de G3NYY |
| Post by MM0FMF on 26th May 2012 at 13:38 |
| In reply to G3NYY: >Class B Free Zone More importantly, no repeaters so no repeater type operating standards :-) Andy MM0FMF |
| Post by G7LAS on 26th May 2012 at 21:30 |
| In reply to G3NYY: Stunned in the face of total brilliance! :) All the best, Rob |
| Post by G8XYJ on 26th May 2012 at 21:57 |
| In reply to G7LAS: What *exactly* about 4m makes it "excellent"!??? -PMR rigs cheap - varying between 30-70 pounds for a 25 watt rig -Simple antennas easy to build and not as big as 6m -Sporadic E in the summer, working Croatia on FM was a highlight, Portugal and Denmark on SSB with 10 watts! -Unlike 6m you don't have people running 400 watts into a huge beam, instead modest setups and limited top 160 watts. -An ever expanding band across the continent. -Effective over reasonable distances. -JT6M Mode allowing for effective QRPP work. -No Repeaters and none of the numptys you get on 2m FM -70.4375 allows experimentation like parrot boxes, Internet links! Why do yo think so many PMR companies use low band 66-88 MHz! Honestly Rob I have been licensed 10 years and have used this band for 9 of those!! After 2m SSB it is my favourite band! Give it a try, 45 quid will get you a 25 watt PMR rig and yo can make a dipole for about 10 pounds!! A bargain if you ask me. 73 Matt G8XYJ |
| Post by G0VOF on 26th May 2012 at 22:21 |
| In reply to G7LAS: Hi Rob, Of course, 4 metres does have more going for it than the above might suggest ;) (Edit: posted before I saw Matt's post immediately above) It is less crowded than 2 metres, & with the influx of "cheap" hand helds that cover the band, & the ease with which you can make an antenna for the band out of 300 Ohm ribbon feeder, it does have some genuine reasons for use. It does have its own propagation characteristics, as all bands do if you study them. It benefits from eS when 2 metres doesn't get a look in, & while it is not permitted in as many countries as 50MHz, it is quite an eye opener to be stood on a hill with an FM handheld & J-Pole & hearing Europe at 59+. Under those conditions 4 metre inter EU S2S's would be easy, but mostly, at least in the UK it appears to be a connoisseurs band, with those that use it, actually putting some effort in to what they enjoy. While I can understand the comments about "repeater operating standards", this is not the case everywhere, & should certainly not be attributed to former class "B" operators, which many of us here once were. I was a G7 for about 12 months but I wanted access to HF so I did the 12WPM Morse test in order to gain that. Many class B operators were never interested in HF so didn't bother with the test. With the scrapping of CW competence as an official requirement for HF access, at least in the UK, all class "B" license holders were granted full HF privileges. Are the HF bands better or worse now? That would purely be a matter of opinion, but I am quite happy to work anyone with a callsign, & if it keeps the amateur bands active & used, then it must be a good thing. Returning to the subject, 4 metres offers more "bendyness around the terrain" than 2 metres,with an antenna only twice the size, & the possibilty of eS much more often. 50MHz offers more of this, & despite most people having radios that cover 6 metres, it remains even more rarely used for SOTA than 4 metres, at least in England. For the cost involved, & the reward to be gained, 70MHz has got to be worth a punt. Best 73, Mark G0VOF |
| Post by G3CWI on 27th May 2012 at 08:45 |
| In reply to G0VOF: > Returning to the subject, 4 metres offers more "bendyness around > the terrain" than 2 metres,with an antenna only twice the size, > & the possibilty of eS much more often. It is certainly true that lower frequencies diffract over obstructions better. It is also true that Es is more useful at 4m than at 2m (and Ms) however, a glance at the VHFAC results for a comparison of 2m with lower frequency bands shows an interesting difference. Basically the tropospheric modes of propagation are more effective on 2m than on the lower bands. These modes are actually relatively reliable (cf Es at least). The ODX comparisons under flat conditions show why 4m and 6m are disappointing bands under flat conditions that prevail. In most cases I would say that 2m offers the best "bang for your buck" on VHF. 73 Richard G3CWI |
| Post by M1EYP on 27th May 2012 at 09:49 |
| >Well, in days gone by, it was a "Class B Free Zone". Not even CW is class B free now... Tom M1EYP |
| Post by G3NYY on 27th May 2012 at 10:34 |
| In reply to M1EYP: > Not even CW is class B free now... ROTFL! And more power to your elbow, Tom ... quite literally! :-) The HF bands have been buzzing this weekend. 15 and 20 were open to North and South America all night, and lots of VKs on 20m this morning. 73, Walt (G3NYY) |
| Post by MM0FMF on 27th May 2012 at 19:53 |
| In reply to G3NYY: Bah 15 and 20 were end to end with CW stations all calling some station called TEST. Everyone was calling, nobody was answering :-( No ability to self spot or get spotted meant calling CQ SOTA on 18.086 was a lonely and fruitless pastime. Took a while to get found "in the near of" 7.032 even! Thanks Roy. Andy MM0FMF |
| Post by G3NYY on 28th May 2012 at 11:04 |
| In reply to MM0FMF: LOL! You could have worked just 4 of the contest stations in a couple of minutes, Andy, and that would have been your summit qualified. QED. :-) 73, Walt (G3NYY) |
| Post by G3NYY on 31st May 2012 at 08:12 |
| There has been a lot of Sporadic E on 4m in the past couple of days. On SSB and CW I have worked EA, CT, OY, ON, S5, 9A and YO. Also heard some Italians and a new Greek beacon, SV8FOUR/B on 70.0732 MHz. To bring it back on topic (well, almost) I also had the pleasure of working old SOTA friend Jozsef, HA5CW, on 4 metres CW yesterday. Unfortunately, he was located in Essex operating as M0HAA/P (non-SOTA)! 73, Walt (G3NYY) |
| Post by G8XYJ on 31st May 2012 at 10:52 |
| In reply to G3NYY: Well done Walt It looks like it is time to get my 3 ele 4m beam back up in the Garden!! Delta loop bye bye, DX on 4 Hello!!! 73 Matt G8XYJ |
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