Welcome to Tropical band

To most people the phrase "tropical bands" bring a pretty clear picture to mind - a bunch of shirtless guys playing calypso music. But to experienced shortwave DXers those two little words express the most challenging and enjoyable part of the radio hobby. The phrase kindles memories of a DXer's best catches and favorite QSLs, of exotic stations, music and of early morning listening sessions. (Don Moore)
I like the "Tropical band" name for new 60m allocation. (OK1RP)

Effective from 1st Jan 2017 please paper QSL via OM-bureau only.

Wednesday, February 16, 2011

Sunset-watchers on 5MHz by Peter, G3PLX


I notice several groups of 5MHz operators working each other around sunset,
waiting for the skip to fade. Stations close to each other fade out first followed by those further apart. The more northerly paths will fade-out earlier that the southerly paths. It's fascinating to experience this, especially if you haven't studied it closely before. It's also quite surprising how quickly signals on a particular path can vanish.

However, I note that some people keep a close eye on the local sunset times
and have grey-line maps available, and seem to be expecting that there is something 'magic' about the precise time at which the sun sets. This is all wrong.

The propagation mode in use on 5MHz around the UK at sunset is almost
certainly via the F layer, which is at a height of approximately 300km. For a particular path, the relevant part of the F-layer is that which is above the midpoint of the path. If sunset has ANY significance at all in this matter, then it's going to be sunset at this point on the F-layer, not sunset on the ground.

If the sun is just setting on the ground, it will still be shining at a
height of 300km, and a few quick calculations shows that the terminator (the grey-line) will be some 1800km displaced from the ground-level terminator. F-layer sunset will be more than an hour later than it is on the ground. If we were really concerned about precise sunset times, we should calculate it for the height of the ionosphere, not at sea level.

However, this isn't the whole story. At ground level we are familiar with
the fact that it gets dark suddenly as the sun drops below the horizon and this visual phenomenon would still apply at the height of the F-layer. However the ionisation level doesn't drop suddenly when sunlight vanishes. Free electrons hang around for hours at this height and there's a slow decay in the critical frequency, not a sudden drop. Study of the FXi figures on the Chilton or Fairford ionosonde websites will confirm this. Indeed the critical frequency starts to drop several hours BEFORE sunset. This is simply because of the shallower angle - a given amount of solar radiation is spread over a larger area of the ionosphere as the sun moves further away from the zenith.

All of which brings me to the point of this posting. It's true to say that
the sun sets later in summer and it's also true to say that 5MHz stays open later in summer, so it does make sense to run tests like this progressively later as the months go by but there is no significance in the precise timing of ground-level sunset.



Friday, February 11, 2011

Texas on tropical band - US State #8

Hi all,

Unbelieving conditions - excellent score tonite.

I worked Frank, K9HMB with 58 peaking 59+ over here. His signal was so strong that I did not believed it's not hijacked callsign! Frank was for me US State #7 from Illinois. Then after I was called by Les, K4DY from NC with his nice 57! Also very strong and clear signal and we managed very nice QSO.

After I set another trial with Charles, K5SUL from TX. After almost 30mins of trials and several QSYs from QRMed channels to another one we managed correct QSO with 449 report for me and 34 report for him. Very hard job on both sides.

Interesting conditions tonite. After several calls Charles sigs fall down and I was not confident as Charles reported the same with my signal on his side in TX. We tried it again and 5mins after his sigs jumped out from the noise for very short period. Luckily at that time I hrd crystal's clean report for me. After his sigs went down under noise. As Charles reported in his email after he has to wait for the same situation in TX. My sigs were down and nil cpy. But 5-6mins after my sigs came up and Charles cpied his report correctly! In min or two my sigs again fall down to noise. It sounds like sine wave oscillating of the propagation between Czech and Texas been there with 5mins periods.

It was real challenge and big excitement for us both I gues as we tried to make QSO for more than 5 weeks nite by nite!!! Few times we almost finished it successfully but one of us did not received correct report so QSO failed... We tried SS in Texas then also SS in Czech...nil. Then - several weeks after we managed finally QSO... tonite! I gave to Charles his new one #57 and for me it was new and rare US State for WAS60. Also it is new distance record which is breaking QSO with San, K5YY from AR to my QTH I guess. (Sri San, I have to check who is winner on the web calculator...)

Really excited after hard job and I would like to thanks to Charles, K5SUL for his patience and effort to spend so much time to make just one QSO!

73 - Petr, OK1RP

TF - DXCC #15 on 60m


I am happy to say DXCC #15 is reached.

On 5/2/11 I worked Tor, TF3GW on 5260kHz using CW. If You are wondered what is unique on the TF on Tropical band then be awared that it is on CW... Lot of stations from TF is active on the 60m band but no CW ops unfortunatelly. Even the cross mode QSO was the problem so I really long time looked for some op who will be so nice to make QSO over there on CW.

Tor, TF3GW has setup on country QTH so it was no easy for him to go there because of lot of snow everywhere... finally he was able to come to country QTH and arrange the setup on 60m. The conditions were nice and we made QSO including some short chat.

Thank You very much Tor for Your willingness and very nice QSO. It gave me new one #15 on 60m!

73 - Petr, OK1RP