Re: Topband: Topband loading coil
Jim, I have an Rig Expert AA-200 analyser, which is excellent for this sort of thing, shows a proper swr plot on the screen, better than the MFJ unit. On 80m at 3637kHz, swr = 1.4:1, R 35.3, Z 35.3, X -2.3, C 19069pF on 1900kHz with the loading coil in place, swr = 2.5:1, R 20.9, Z 22.9, X -9.3 C 9035pF. swr is >10 without the coil on 1900kHzThe weather has been dryish all week and when I did the previous tests the weather had been wet for a week so ground conductivity is almost certainly playing a part in this. 73 Max M0GHQ > Date: Sat, 6 Jun 2015 08:32:06 -0700 > From: j...@audiosystemsgroup.com > To: topband@contesting.com > Subject: Re: Topband: Topband loading coil > > > > Ideas what to do next > > Borrow an antenna analyzer and measure the antenna's feedpoint impedance > with a very short piece of coax (in other words, right at the base) with > and without the coil. > > 73, Jim K9YC > _ > Topband Reflector Archives - http://www.contesting.com/_topband _ Topband Reflector Archives - http://www.contesting.com/_topband
Re: Topband: Topband loading coil
Just chopped the fibreglass webs out and now no change, I would not have thought it would affect this coil, so something else must have altered since two days ago (Had to work) affecting the way the SWR is reacting.Pity, I was pleased with the result, now to try to increase the Q of the coil without altering the resonance, I cannot go longer on the top wire as it would extend over my property boundary, hence the loading coil.73 Max M0GHQ _ Topband Reflector Archives - http://www.contesting.com/_topband
Topband: Topband loading coil
I have an inverted L antenna resonant on 80m, I decided to add a loading coil to the base to bring it on frequency for TopBand. I wound a 2.5mm wire coil 16 turns on a bit of square Paxoline board by drilling holes into the board each side and feeding the coil through the holes, a bit of a struggle but it worked, not very pretty, it is 146mm diameter and 120mm long 30.5uH. When I first tried it the SWR after small trimming was 1.2:1 band centre and 2.0:1 band edges. Now it looked a but ugly, so I decided to neat it up a bit by adding two fibreglass webs so the coil was now circular and held by a cross section instead of just the one plane, now when I retried the SWR it is still resonant on 1.800 but the SWR is now 2.0:1 in the middle of the band and 4.0:1 at the edges the turns are the same, the inductance is the same but I have lost my fine SWR curve. I only added the fibreglass and neated up the coil, Ideas what to do next apart from removing the fibreglass webs and goin g back to ugly coil?73 Max M0GHQ _ Topband Reflector Archives - http://www.contesting.com/_topband
Re: Topband: K1N DQRM Tracking Project
I think the fact that something positive is being done is working, even if it is electrically futile it is definately putting some DQRM'ers off, the DQRM has been noticeably less and with K1N ops and others reminding the offenders that something is happening is a plus. The triangulation would only really work if the reports are simultaneous with vertical antennas of the same gain and calibrated receivers, otherwise beam headings, propagation etc come into play. Thankfully most of the troublemakers are probably at the lower end of the intelligence scale so do not realise the problems. Maybe one or two high profile prosecutions will discourage some too. Anyway, if it reduces just a few every time it is a positive move. The K1N ops are doing a brilliant job in the given conditions, well done to them.73, Max M0GHQ _ Topband Reflector Archives - http://www.contesting.com/_topband
Re: Topband: Rig Question
It's not that long ago when everyone would be raving about the Drake R-4C , so many pictures of top Topband Dxer's with one on the table, how times change. 73, Max M0GHQ/W8BX _ Topband Reflector Archives - http://www.contesting.com/_topband
Re: Topband: Verifying integrity of 75 ohm coax. ( silicone grease)
Actually, that flies in the face of everything published about typical silicone dielectric greases. Tom, I would tend to agree with you on this point, maybe it was the switch just breaking down ( Only digital signals no high voltages) and the small metal particles were causing further damage when loaded into the grease. Difficult to tell. I was surprised however and originally put it down to what I have just described. The Potable silicone grease was a local hardware company supplied item, cannot find the can just at the moment though so cannot put a name to it. Worked very well for the original purpose which was to introduce into the SO-239/PL-259 connection on my Steppir antenna, never had any water ingress from there on. 73, Max M0GHQ _ Topband Reflector Archives - http://www.contesting.com/_topband
Re: Topband: Verifying integrity of 75 ohm coax. ( silicone grease)
Very soon afterwards (a few weeks instead of perhaps a year), the operator called me over to show me the problem with that switch. I know what I saw, and I am convinced that it is abrasive. That grease accelerated the failure of that switch by a tremendous amount. This is very interesting and something I also discovered and never reasoned why, I have used Potable silicone grease inside PL-259 coax connectors and never had a problem, however, when I have used the same grease inside the rotary preset switch for my Prosistel rotator controller box it destroyed the switch in a couple of months, now I know why. Thanks for the interesting thread. 73 Max M0GHQ _ Topband Reflector Archives - http://www.contesting.com/_topband
Re: Topband: Local noise source identification
Check out UKQRM on google, plenty of information there including soundbytes. 73 Max M0GHQ _ Topband Reflector
Topband: Dogleg BOG antenna.
I am going to try to place a BOG antenna in my local neighbourhood, as I don't have a 650+ foot garden I thought the most inconspicuous antenna would be a BOG, however I have to 'Dogleg' it, it has to run for 200 feet North, then 200 feet East and the remainder North again, I only have a maximum run of 700 feet. I will terminate it with a 200-470 Ohm (select test) resistor at the far end, I have to run this along a wooden fence line opposite a metal mesh fence about 10-15 feet away for the entire run, this is towards the East. The mesh fence is enclosing an industrial area with a footpath running around that enclosure. My intended BOG will be on the side of this footpath away from the metal fence. Maybe I am wasting my time, has anyone done anything like this, I do have a North/South 'Inverted L' antenna but it is not brilliant for TopBand as I can only ever hear UK and EU stations and normally not even those. I can base load the 'L' but that is not brilliant. Ground conducti vity is good as I am about a mile away from a river and 3 miles from the sea, good for HF but maybe not so good for LF bands. Maybe just adding a few more topband radials to my 'L' may work for the moment. Ideas on this anyone? QTH is South England. 73 Max M0GHQ ___ UR RST IS ... ... ..9 QSB QSB - hw? BK
