I remember hearing that during the winter months, fm signal quality sort of degrades. Ive noticed my quality has dropped some in the past month or so. Im trying to figure out whether this is a problem with my transmitter or just a seasonal thing. My signal goes as far as it always has, but once I get a mile or 2 from the transmitter the quality is a little more 'crackly'. The only way I can think to describe it is like listening to a very low quality mp3. But in my house and nearby is sounds crystal clear. Im getting ready to move so when I do Im going to check all my connectors and take some good swr readings. But other than that I don't know what to do. It sort of bothering me and Im debating on ordering a new transmitter.
Any thoughts? Or any experience with this phenomena and what the symptoms are?
Hmm I have noticed at winter time here that FM reception degrades some for far away stations that normally pick up well in summer. It could just be my stereo system though . I don't have a good answer for this. Usually seasonal changes only effect the lower HF frequencies (3-30MHz). I would not doubt it one bit though if there is some effect on lower VHF bands like those used for FM broadcast. I will have to look into it . Definitly keep an eye on that SWR. If the SWR reading is fine and you're cranking out as many watts as normal, then probably is a problem at the receiving end. Best of luck.
Post by sgtpeppers on Jun 14, 2011 23:19:34 GMT -6
I notice rainy days even effect radio stations in my area, although i live on a mountainous island surrounded by other islands like mine. snow, rain, fog, and i found the worst is high smoke from forest fires. Weather can dramatically change your signal.
Depending on the location, usually the winter months tend to wreak havoc with FM..especially when there is all that white stuff on the ground and in trees and on rooftops...not to mention icing of receiver antennas!
The FM broadcast frequencies are subject to the same issues as UHF and microwave. They will "bounce" off of objects and can be absorbed as well causing signal path loss. Beam tilt is used to bring that signal down to the horizon because VHF likes to venture out into space and try to reach Orion. Now on a system that does not use beam tilt on the antenna, that signal is mostly traveling upward and into space. Now imagine what it does when the ground is covered with a reflective material such as frozen water particles! Acts like a huge reflector, but it can also act like an attenuator..absorbing what little signal stays on the horizon, thus reception is affected as well as effective coverage for a given power level transmitted.
The technical terminology is called "Temperature Inversion". An example of overcoming this phenomena is the older 2 Ghz and 7 Ghz microwave links used in STL applications. The tower site, or receiving point would usually incorporate two receiver dishes separated by some height from each other. This would allow the top dish to pick up the temperature inverted microwave signal as it literally bends upward due to temperature changes along the path length. Long paths were always plagued with this phenomena.
Also FM is line of sight, so topography plays a part too. It might be clear ground at point A (receiver) and point Z (transmitter site) high up on a hill 75 miles away...but what makes the huge impact is what is in between those two points, and what may cause those unknowns to have what kind of effect on that signal path during different seasons.
It could be a snow covered tree, or large building blanketed in snow, or wet from rain, both of which affect FM signal propagation dramatically. Cloud coverage can also affect FM signal propagation. It can go one of two ways...either help the signal stay on the horizon, or even prevent that signal from being as strong as it would be by deflecting most of that signal above the cloud layer and away from the horizon. This can also happen in reverse, where a cloud layer helps a distant station signal continue along the horizon due to the reflective effect by the cloud layer, thus stations a few hundred miles away can easily be picked up as if they were across town.
About the only frequencies not really affected so much by these things are the LW/MW and SW bands.
Back in 1997 while chief engineer for KPEJ Fox 24 in Odessa Texas, which was a 4.5 Megawatt ERP UHF tv station, we got a reception report from the southern part of Mexico. They even recorded the reception onto a VHS tape. Neat thing about this reception report was that they used a VHS HI-FI machine and the tv station was transmitting stereo audio with 1 SAP channel. The recording clearly demonstrated they were receiving full BTSC stereo audio as well as the SAP channel, and the video was very watchable with just a little bit of noise. This took place during the winter season in 1997 when in that year, Odessa Texas got an unusual amount of winter snow. West Texas is flat land and dry desert. When that vast desert got covered with a layer of snow, and a cloud layer filled with ice water particles covered the entire area, and with a UHF antenna sitting at 1,340 feet up pumping out 4.5 Megawatts ERP, the ground and cloud layer acted like a wave guide and carried that signal for thousands of miles.
Who says UHF cant carry!
AM Stereo 1670
FM Stereo 92.1
Great information RFBurns. It's interesting and quite an educational endeavor learning how weather indirectly affects radio transmission.
I have always noticed that Autumn is the best for FM broadcasting over here. When those leaves fall the trees let my signal pass through more easy. Being in an area with a lot of trees can be problematic. For tropospheric ducting (long distance skip on FM) I have been able to receive stations on FM at great distances. I have no idea if the same goes true for pirate broadcasting power levels being heard many miles outside of their usual range though. It sure would be interesting to know if I have ever had my signal heard hundreds of miles away with only watts of power.
Medium Wave AM broadcasting seems to be a different story. I always get the most skip for reception and farthest broadcasting range in Winter. On a nice winter day I have heard my AM broadcast for many miles w/o any static on a clear channel. Winter and MW seem to go together nicely.
Post by highmountainradio on Jan 12, 2018 21:37:40 GMT -6
Hi Kage !
Indeed it is VERY possible for pirate radio broadcasts to be heard hundreds if not thousands of miles away depending on propagation disturbances, time of year, E Layer (Hundreds to Thousands of Miles) or F2 layer (tens of thousands of miles). The Sunspot Cycle presently is in the toilet but DX can still occur with just the right conditions. A friend communicated with New Zealand on 50 MHZ here about 1.5 years ago at the low end of the cycle ! Of course that was with 1500 Watts and highly directional antenna but still it's stunning !!