Home |
Search |
Today's Posts |
|
#2
posted to rec.boats
|
|||
|
|||
VHF vs CB Antenna?
On Thursday, November 29, 2018 at 2:23:30 AM UTC-5, wrote:
On Thu, 29 Nov 2018 00:59:42 -0500, wrote: On Wed, 28 Nov 2018 18:48:18 -0500, wrote: IBM collected a lot of hams. Back in the days when I was in DC they were already migrating to digital, hooking ASR33s (teletype) to their ham gear. Some still worked 2 meter radio telephone but not that much. The guy from Ft Myers who retired in Tennessee says they have a pretty active ham group there but they are connecting up PCs. I guess ham has become just an RF modem. === Digital comms is sort of on the cutting edge of ham technology these days although it goes back more than 15 years at this point. There is a device called a Pactor modem which acts as a combination modem and packet encoder. It attaches to either a ham rig or commercial marine tranciever, and allows error free transmission at speeds up to 4800 baud under good conditions. It's fairly sophisticated in its operation, automatically adjusting speed and re-transmissions based on radio conditions and error rates. I use it when we are cruising in the boondocks for EMAIL, weather, stock market quotes, etc. http://www.docksideradio.com/ptcii.htm We ran 4800 BPS modems here in Ft Myers to get to the office network from home. As long as you were just using text and maybe some low resolution pictures it worked great. When the V.32bis (~14.4Kbps) and V.34 (19.2Kbps) stuff showed up we were awed. I am surprised they can't get that trellis modulation stuff running on RF. We were doing it on nasty dial up lines at 2400 baud. (not the same as bps) The baud is 2400 (basically the frequency of the carrier and about all dial up can deal with) They then pick off 8 data bits from every wave. (19.2) 4800 bps is only looking for a bit at each peak. (2x baud). Maybe RF can't beat unshielded copper. The problem isn't RF. LTE is RF, and speeds approach 50mbps. |
#3
posted to rec.boats
|
|||
|
|||
VHF vs CB Antenna?
On Thu, 29 Nov 2018 02:23:09 -0500, wrote:
On Thu, 29 Nov 2018 00:59:42 -0500, wrote: On Wed, 28 Nov 2018 18:48:18 -0500, wrote: IBM collected a lot of hams. Back in the days when I was in DC they were already migrating to digital, hooking ASR33s (teletype) to their ham gear. Some still worked 2 meter radio telephone but not that much. The guy from Ft Myers who retired in Tennessee says they have a pretty active ham group there but they are connecting up PCs. I guess ham has become just an RF modem. === Digital comms is sort of on the cutting edge of ham technology these days although it goes back more than 15 years at this point. There is a device called a Pactor modem which acts as a combination modem and packet encoder. It attaches to either a ham rig or commercial marine tranciever, and allows error free transmission at speeds up to 4800 baud under good conditions. It's fairly sophisticated in its operation, automatically adjusting speed and re-transmissions based on radio conditions and error rates. I use it when we are cruising in the boondocks for EMAIL, weather, stock market quotes, etc. http://www.docksideradio.com/ptcii.htm We ran 4800 BPS modems here in Ft Myers to get to the office network from home. As long as you were just using text and maybe some low resolution pictures it worked great. When the V.32bis (~14.4Kbps) and V.34 (19.2Kbps) stuff showed up we were awed. I am surprised they can't get that trellis modulation stuff running on RF. We were doing it on nasty dial up lines at 2400 baud. (not the same as bps) The baud is 2400 (basically the frequency of the carrier and about all dial up can deal with) They then pick off 8 data bits from every wave. (19.2) 4800 bps is only looking for a bit at each peak. (2x baud). Maybe RF can't beat unshielded copper. They get away with higher rates by using better error correction algorithms. A clean line will run at the rated speed and it starts falling off fast from there. At a certain point the modem will kick down to a lower speed until it finds one that works. That sounds like what you have too. Cool stuff tho until they get the couple hundred satellites they want up for broadband connections. === The Pactor speeds are limited by FCC regulations designed to minimize bandwidth and adjacent frequency interference. Of couse HF SSB is also much noisier and susceptible to fading than a telco landline. The automatic re-transmission of error packets and adaptive signaling is very cool however, and quite useful for short messages, weather data, etc. --- This email has been checked for viruses by AVG. https://www.avg.com |
#4
posted to rec.boats
|
|||
|
|||
VHF vs CB Antenna?
On Thu, 29 Nov 2018 14:39:08 -0500,
wrote: On Thu, 29 Nov 2018 02:23:09 -0500, wrote: On Thu, 29 Nov 2018 00:59:42 -0500, wrote: On Wed, 28 Nov 2018 18:48:18 -0500, wrote: IBM collected a lot of hams. Back in the days when I was in DC they were already migrating to digital, hooking ASR33s (teletype) to their ham gear. Some still worked 2 meter radio telephone but not that much. The guy from Ft Myers who retired in Tennessee says they have a pretty active ham group there but they are connecting up PCs. I guess ham has become just an RF modem. === Digital comms is sort of on the cutting edge of ham technology these days although it goes back more than 15 years at this point. There is a device called a Pactor modem which acts as a combination modem and packet encoder. It attaches to either a ham rig or commercial marine tranciever, and allows error free transmission at speeds up to 4800 baud under good conditions. It's fairly sophisticated in its operation, automatically adjusting speed and re-transmissions based on radio conditions and error rates. I use it when we are cruising in the boondocks for EMAIL, weather, stock market quotes, etc. http://www.docksideradio.com/ptcii.htm We ran 4800 BPS modems here in Ft Myers to get to the office network from home. As long as you were just using text and maybe some low resolution pictures it worked great. When the V.32bis (~14.4Kbps) and V.34 (19.2Kbps) stuff showed up we were awed. I am surprised they can't get that trellis modulation stuff running on RF. We were doing it on nasty dial up lines at 2400 baud. (not the same as bps) The baud is 2400 (basically the frequency of the carrier and about all dial up can deal with) They then pick off 8 data bits from every wave. (19.2) 4800 bps is only looking for a bit at each peak. (2x baud). Maybe RF can't beat unshielded copper. They get away with higher rates by using better error correction algorithms. A clean line will run at the rated speed and it starts falling off fast from there. At a certain point the modem will kick down to a lower speed until it finds one that works. That sounds like what you have too. Cool stuff tho until they get the couple hundred satellites they want up for broadband connections. === The Pactor speeds are limited by FCC regulations designed to minimize bandwidth and adjacent frequency interference. Of couse HF SSB is also much noisier and susceptible to fading than a telco landline. The automatic re-transmission of error packets and adaptive signaling is very cool however, and quite useful for short messages, weather data, etc. If they are stealing from the v.32/34 model they are also using ECC correction that will plug in a couple of missing bits most of the time. It has been a while (almost 30 years) but I think you lose a byte or two overhead in a packet but it can correct 1 or 2 bad bits. It was pretty much just magic for us since it was a chip buried in the hardware. As long as they don't go nuts with the graphics and multimedia 4800 bps is plenty |
Reply |
Thread Tools | Search this Thread |
Display Modes | |
|
|
Similar Threads | ||||
Thread | Forum | |||
TV antenna | Electronics | |||
FS ICOM AH-4 Auto Antenna Tuner with Long Wire Antenna Kit... | Cruising | |||
FS ICOM AH-4 Auto Antenna Tuner with Long Wire Antenna Kit | Electronics | |||
FS ICOM AH-4 Auto Antenna Tuner with Long Wire Antenna Kit | General | |||
vhf antenna | Electronics |