Wednesday, May 28, 2008

SY3M, the photo album

You can see the SY3M expedition photo-album by following this link

SY3M 2008 WPX-CW by the "rats terminators" contest group

Operators: Nico SV3SJ, Pat F6IRF
QSO details and claimed score here TRX: K3 + TT Titan, pro2 + AL1500ANT: 2el SteppIR @9m, Ground-mounted vertical Half-Moxon (40m), 16m ground mounted vertical (80/160), K9AY RX-loop and 120m beverage to JA
MSC: N1MM, Microkeyers, laptops, ICE filters, 700m of wire, 250m of coaxial, 200m of rope and a lot of enthusiasm and energy to setup/dismantle all this !!!
Under Max's hass, some of the hardware used for the operation !
My initial personnal plan was to go back to CN with some ambitions in the SOAB category, but for some obscur administrative reason the licence never arrived. On his side, Nico had already planned a trip to his home country... I could not miss such an opportunity to go back to wonderful Greece, so we quickly improvised something to be on the air; not to be competitive, but to take part, which is the most important as says the Olympic games chart! (another famous Greek/French joint venture !)Among the difficulties to setup a all-bands M/S station from scratch in a remote location, the first one was to rehabilitate a house, unnocupied by humans for some 20 years (adopted by rats and mices and invaded by wild vegetation); It took a few days to make the house usable, but we managed it... The cohabitation with the dense rats population was not always easy, but they finaly accepted to free-up some space for us (must say that we had to insist a bit, using some powerful unfair arguments... the main problem for me with the Greek rats, being that that they understand only Greek and they start working at sunset until sunrise...).Waiting for Nico to complete some "non-ham" obligations and beside some 6m and peri-contest activity (about 800 Q's as SV3/F6IRF ), I started by installing my 16m multiband portable HB vertical, tested the week before in britanny.

The 16m vertical used for 80 and 160. Alone it consummed some 300m of radials...
After a few tests on the air, I started to think about some more efficient solution for 40m, which is key band in this contest. We needed something simple, that we could setup quickly with the hardware we had (2 fiber 10m telescopic masts), so after a few simulation sessions we decided to go for a vertical "half-moxon" mainly for his broad horizontal pattern (a description will be published later here). Must say that the results overtook my expectations, the difference with the vertical being obvious right from the first listening tests. It was confirmed during the contest, as we did not get any problem to break the pile-ups and get DX stations to call us.
The vertical base; despite the poor ground quality, it worked fine...
Obviously the weak band has been 20 meters, due to the low height and limited gain of the antenna, but we could not do better for this time...10m provided some nice openings, including to JA (most probably multi-hop E's) and 15m a nice combination of E's and F2 propagation.
The driven-element of the half-moxon which gave us a strong signal on 40m. Another 200m of radials !!!
At the end we are just short of multipliers to be "almost competitive"- we had initialy planned DX-cluster through a VHF packet-link to Kalamata, but the distance and terrain profile between Kalamata and Pilos area did not allow it to work. We obviously also missed a second antenna on the high bands - but we did no expect them to be so productive and to say the truth we ended up short of time and energy (the temperature on those days did not help) ! - Anyway, in may still be a new Greek M/S record...
The SteppIR at 9m. On 20m difficult to compete with fixed stations using large antennas or stacks at a decent height.
I really enjoyed those 2 weeks in this still preserved paradisiac wild area... unfortunately not for long, as in many other places, the "beton" is about to win (a large touristic ressort is already in construction, a Motorway is scheduled and the promoters all around). A special mention to the Greek local people for their "way of life", sometime a bit annoying for a stranger, but so nice at the end !
73's from Sunny Greece - Pat
PS: More to follow here soon
including a video for which I have a lot of raw material...

Wednesday, May 07, 2008

WSPR 80m tests from IN87

The above plot shows the 80m WSPR-data collected from W1XP (FN42fo) and my portable station (IN87nn) during 4 nights, from May3 to May7 (about 250 spots). 4 to 10W were used on both sides but all plotted levels are normalized to 1W.
The general trend, over the 4 nights is a 6 to 7dB offset in favor of W1XP transmitter, with a 10dB peak around 01:30. This may indicate a higher TX antenna performance or a higher noise floor (or both) at W1XP. It is interesting to note that at W1XP sunset (when the band opens for him), he seems to hear me better. As suggested by ON4UN in "low band DXíng", the explanation may be linked to a lower noise level while the D-layer is not yet fully dissipated. This is confirmed by the below VOACAP Noise-power plot for Boston area, where we can see that on 3.5Mhz, the noise is minimal 3 hours before sunset and maximal in the middle of the night (The below graph is for a very quiet site, the variation may be partly or totaly cancelled or changed if the main source of noise is local). Those variations, although the power and antennas gain remain constant, do not mean that the propagation is not bilateral,just than the noise is not distributed equaly at both locations. The 7 dB offset trend clearly means, that my TX antenna does not work as well as W1XP's one (unless some problem on W1XP's Receiver, signal treatment, QRM,QRN, birdies, etc...). The only way to know would be to compair with a third station used as reference.

Sunday, May 04, 2008


One example of last night 80m session. As usual all levels are normalized to 1W. Apparently my 80m portable antenna is working fine...
The portable antenna, just a bit shorter (16.5m) than my home one, but built on the same principle (see the best of this blog). Built with a light telesopic mast, a steppIR fiber element, and a a light fishing rod.
Just a dozen of 10m radials laying on the ground, enough to get the radiation resistance close to 28 ohms on 80m. Matching is just done by a serial coil and 28/50 ohms UNUN.

Friday, May 02, 2008

Is the propagation always bilateral ?

Having done, quite a few "single band" contests along the past years, I had noticed more than once, that at band opening /closure, a few DX stations could be heard at a decent level, even at strong level, but that it was impossible to get through. Until a few days ago, my opinion was that it was because the band being wide open for them, they had stronger QRM level.
I must say that the following graph changed my opinion... at least I have a serious doubt...
Above is the plot made from WSPR 30m spots between Joe K1JT and my station during the 2 first weeks of April. As usual SNR's have been adjusted to take into account the TX-power variations (all SNR's being normalized as if both stations were using 1W).
I had noticed Joe spotting me quite frequently in the morning, while I could not hear him at all. Thought that it could be explained by a lower noise floor at his location. Plotting the above, introduced a doubt, especialy this 2h30 offset between the maximums... (the max being moreless equal). If you have an opinion about this interesting question, or if you want to repeat the same kind of plot with another pair of stations (the data is available for everybody in the database) you are welcome !

Is my K9AY working as expected ?

Following is another example of the interest of WSPR and the network of bidirectionnal beacons that is building up. Last night the activity focused on 80m band; a good opportunity to test the RX performance of my K9AY-loop versus my vertical. Once again I used my automatic switching system (see previous posts) to switch from the vertical to the K9 every ten minutes. I inserted a step attenuator in the TX antenna line to the RX, to balance the noise floor on both antennas (and avoid soundcard input overdriving). Following are a few results, based on limited number of spots, but which IMHO already give interesting indications (as for any statiscal method, more samples more accuracy). As for the previous plots published on the blog, all levels are normalized as if the transmitted power was always 1W - Of course it assumes that the operators are honnest, with their claimed power level, but for this particular exercise it does not really matter. The beauty of WSPR is it provides directly the SNR (Signal to Noise Ratio), which is the most interesting parameter when you want to compair receiving antennas.
First is the theoretical pattern of the K9AY, with the direction of the considered stations (I took the station that I copied more often, taking care that I had a balanced number of spots on each antenna). the pattern is for 30 degrees elevation... to be more accurate, the pattern should be considered for the circuit elevation, but this is just an indication. The important follows...

We can see on this first plot that the K9 is much better for G4MQL, while the vertical is more favorable to F1VS, especialy in the evening. By the way we can see the propagation drop at short distance during the night...

The second plot is for SV2BBO... I leave you to make your conclusions...

Finaly are the plots for several US stations, and for VE1RG and VE1VDM ( I put their spots together, as they had equal number of spots, and they are not that far away from each others).
So now, I think that we have the answer to the inital question: Is my K9AY working as expected - YES !
What is the benefit of such a receiving antenna: for my personnal case on 80m, an average 5 to 6dB if the station is in good part of the half-circle. Enough to make a QSO feasible or not ! Not too bad for such an inexpensive antenna which takes very little space ! (mine is a half-size one and only has 1 direction - the least noisy one which is North). Of course in particular DX direction, it won't compete with a long beverage, but I don't have the space for a beverage... ;-)

Thursday, May 01, 2008

A multi-turns magnetic-loop for the top band.

Here is a description of the magnetic-loop that I am using for the 160m band. As shown on the plots published in previous posts, this is the receiving antenna (from many I have tried) wich provides the best rejection of the white band noise generated by the 380kV power line, passing some 200m from my antennas. It is made of 6 turns of RG58 cable (only the copper shield is used) on a PVC structure. The square has 0.8m by side, so 20m of cable are required. The loop is loaded by an adjustable capacitor (required value about 65pF), the coupling to the feedline is made through a small delta loop, matched with a 1/4 balun (200 ohms port to the bottom of the delta). The magnetic loop is made of 6 turns of RG58 cable on a PVC structure. You can see the power line behind ! Best power line noise rejection is obtained with the loop a 90 degrees. The measured line noise rejection is approximately 12dB, enough to make stations to emerge... You can see the loop bandwidth on the 756 spectrum display. The horizontal scale is 20kHz/div while the horizontal scale is 10dB/div. Very narrow ! For my noisy location, using the 20dB transceiver preamp, provides enough level to get the noise floor to S4 with a 2.4kHz filter, so no additional preamp is required.The MMANA-model, seems to match quite closely, the real antenna. The measured SWR is about 1.5 at resonnance, good enough for a receiving antenna... On the model the capacitor is at the top of the loop (just beacause it was easier to draw!). On the real one the capacitor is in the small electrical box at the bottom of the loop (it does not change anything !).The simulated pattern. The horizontal pattern is for the loop at low height above an average soil for 5 degrees elevation. At higher elevations, the pattern becomes an oval with low directivity, so the directivity is only useful to reject punctual sources of noise arriving at low angles, or local stations on groundwave(front to side rejection is about 30dB on the horizon). The difference between the theoretical rejection and the measured one can be explained by the fact that my noise source is not punctual...