Thursday, 30 October 2014

Antenna hints

Something I was searching for when building antennas is the difference between resonance and impedance. Really, I've learned it when I did my radio exams but when you learn a lot you also forget a lot. So a future reference for myself and others:

R=resistive load, X=reactance

1.) RESONANT FREQUENCY is where reactance is zero ohms, or in some cases as close to zero ohms. Since resistance has nothing to do with resonance, the resonant frequency is NOT
always at the point of lowest indicated SWR (although they certainly can be the same). The most desirable load is almost always the load with lowest SWR, even though it may not necessarily be the point of no reactance (resonance).

2.) An IMPEDANCE of 50 ohms can be composed both resistive and reactive components. If the impedance is 50 ohms, but the SWR is not 1.0 to 1, the likely cause is reactance makes up part or all of the impedance. Contrary to popular (but very incorrect) misconceptions, it is impossible to obtain a perfect 1 : 1 SWR when the load is reactive, even if the complex impedance is 50 ohms.
A good example is a 50 ohm nearly pure reactance load. R=0 X=50, while the impedance meter reads 50 ohms. The SWR would overflow (SWR>25), since the reactive 50 ohm impedance load absorbs almost no power from the source and has a nearly infinite SWR.

3.) Even if a perfect transmission line is cut to an exact electrical half-wave (or a multiple thereof ) it is a true half-wave multiple only on one frequency in that band. On a slightly different frequency the line will not represent the true feedpoint impedance of the antenna. The line is only “impedance transparent” when lossless and when an exact multiple of 1/2 wl. The longer the transmission line in wavelengths, the “more length critical” it becomes and the less accurate measurements become.

4.) If the feedline is not an exact multiple of 1/4 wl, the resonant frequency of the antenna might be shifted higher or lower by the transmission line. A mismatched non-quarter wave multiple feedline adds reactance that can cancel antenna reactance at frequencies where the antenna is not resonant. Multiple antenna and feedline combination resonances commonly occur with dipoles, where reactance crosses zero (indicating resonance) at some frequency other than the antenna’s actual resonant frequency. This is a normal effect.

5.) If the line is a 50 ohm line, has no radiation or parallel currents, and if the line has minimal loss, moving a analyzer to another point on the line will NOT change SWR reading. Impedance and resonant frequency might change from line transformation effects, but the SWR will not change.

6.) If SWR changes with coaxial line length, line placement, or line grounding (any distance away from the antenna) changes, the feedline has one or more of the following shortfalls:
 a.) The feedline is carrying common mode current and radiating.
 b.) The feedline is not a 50 ohm line.
 c.) The feedline has high loss.

We have a clubmeeting tomorrow evening. PA0HPG Harm is going to talk about using a FA-VA3 antenna analyzer and how it helps to make your antennas work. I really like this kind of talks and hope to learn a lot from it. If it reveals something important I will certainly update this post or post a new one about it.


Wednesday, 29 October 2014

CQWW DX SSB 2014 last weekend

Event: CQWW DX SSB ham radio contest
Logger: N1MM+ most updated version
Station: Icom IC-706MKIIG 100W, headset&Turner+3B combined
Antenna: Homemade aluminium tape all band HF vertical with CG3000 autotuner at 9m AGL.
Coax: 50m Belden H1007


JV5A on his morin-khuur, worked 40m
In my eyes this is the biggest SSB contest of them all with the best and rarest DX. If you are a serious DXer you really should participate in this contest even if you never participate contests at all. The propagation was surprisingly good. Although there seemed to be a radio blackout Saturday at 17:00 UTC I didn't experience it as I was not on the radio at that moment. At the hours that I was on the air conditions were great. I started very early before work (3:45 UTC) Saturday morning on 160m and first QSO was with PI4M, Frank PF5T was on the mike and told me he had read my blog about the CQWW wishlist. That was fun! Had to stop at 5 UTC with 60 QSOs in the log, not bad for a hour S&P! I returned Saturday evening at 21 UTC and made as many QSOs as possible including some nice DX like JV5A Mongolia, 9K2HN Kuwait, UP2L Kazakhstan and lots of Canada/USA all on 40m.

I was up early again Sundaymorning and started to work 80 and 40. Lot's of USA and easy to work too. When sunrise was approaching I checked the higher bands regulary. A half hour before sunrise 10m came to live and I easily worked the middle east. My first new DXCC of this contest with S79K was worked with some difficulty at 5:54 UTC and at that time it was still dark (sunrise 6:18). Working DX on 10m with the vertical is not easy but can be done. 10m and 15m were wide open now and I managed to work another station from my wishlist AH0K from the Marianas. Had to stop around lunchtime and returned in the evening when 15m was absolutely crowded with USA/Canada all very easy to work.

Most interesting DX: 

80m: K3LR and lots of other USA, UP2L Kazakhstan
40m: K3LR and lots of other USA, 8P5A Barbados, JV5A Mongolia, UP2L Kazakhstan, 9K2HN Kuwait, VY2RX and more Canadians, P40L Aruba, FM5EB Martinique, WP3C Puerto Rico, HK1NA Colombia, A73A Quatar
20m: K3LR and lots of USA, VY2TT and lots of Canada, HI3TEJ Dominican rep., YV4NN Venezuela, 9Y4W Trinidad and Tobago, KP2M US Virgin Isl.
15m: A73A Quatar, KL7RA Alaska, K3LR need I write more?, VC2T and more from Canada, HK1NA Colombia, KP3Z Puerto Rico, PJ4DX Bonaire
10m: A92GE Bahrain, A61ZX UAE, A71CO Quatar, S79K Seychelles, ZD8X Ascension Isl., JA0FIL Japan, A73A Quatar, HZ1TL Saudi Arabia, VU2RBI India, AH0K Mariana Isl. and of course USA in the morning already, but no Canada.

More stats: 

Participated time: 12 hours, QSOs: 523, CQ zones: 24, DXCC: 78

DXCC map as generated by QSCOPE

Logger

N1MM+ was tested on SSB this time. Configured with my IC-706 in SO2V (Single Operator 2 VFO). The program still didn't work flawlessly. I did need to configure the IC-706 CAT com for 4800bd otherwise connection would be lost in a minute. After that I had to restart the program every hour or so because of the slow CAT connection. It looks like the CAT had a overflow of info, especially jumping in the band map from one station to another with CTRL+up/down. At one time the program had a stack overflow error screen popping up and tried to e-mail the error. Unfortenately for the programmers I have no e-mail configured so the report could not be sent. It would be better to create a file which you can manually attach to an e-mail so it can be send later. However overall I like the new N1MM+ contestlogger a lot.

In general

Great propagation this contest. A lot of participation from rare DXCC. I had limited time but still worked over 500 QSOs and even worked 2 ATNOs. What strikes me sometimes is the ability of receiving or listening from some stations. For example C37NL was heard on all bands, but no QSO. It seems they had problems receiving as I heard many others calling without succes. On the other hand S79K must have amazing ears to catch my tiny signal, I could barely hear him so that had to be the same for him. I didn't stick too long at stations that couldn't hear me, calling 3-5 times and still not being heard is moving to the next one. And...yes, it was a fun contest.

Bloggers worked

Worked OQ5O Franki on 80m, PA0O Jaap on 40m. Some other known non-blogging operators as well.

Zone chart thanks to 2E0HTS Simon


No time & internet

You all probabely think what happened with Bas. Did he participate in the CQWW? What is he doing? Why is he not updating his blog?



Well, things sometimes happening faster then I can write and not like planned. I have no time to update the blog. But I am radioactive (see my list of ATNOs at the right). Besides that we have a large internet interruption in my village, no internet for the time being. So expect some posts but have patience.