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#42
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VHF vs CB Antenna?
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. |
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#43
posted to rec.boats
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VHF vs CB Antenna?
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#44
posted to rec.boats
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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. |
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#45
posted to rec.boats
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VHF vs CB Antenna?
wrote:
On Thu, 29 Nov 2018 01:02:42 -0000 (UTC), Bill wrote: wrote: On Wed, 28 Nov 2018 17:40:39 -0000 (UTC), Bill wrote: wrote: On Wed, 28 Nov 2018 03:06:28 -0000 (UTC), Bill wrote: Mr. Luddite wrote: On 11/27/2018 7:36 PM, wrote: On Tue, 27 Nov 2018 17:47:44 -0500, "Mr. Luddite" wrote: On 11/27/2018 5:22 PM, wrote: I have a uniden CB radio (new) and have an existing larsen wb vhf radio already on my truck. Will this antenna work with my new radio. Derek Can't determine without knowing what freq range the truck antenna is "cut" for. There are two VHF bands, low-band VHF (49-108 MHz), high-band VHF (169-216 MHz). Marine radios operate in the high band. Generally it will receive ok but transmit range may be limited due to high standing wave ratio (SWR). Even a marine VHF antenna should be tweaked in terms of length to minimize SWR in the middle of the radio's freq range. He is talking about CB (27mz) so that is over twice the wavelength of the lowest frequency VHF. SWR is really going to be ugly but since they are capped at 5w, (usually more like 4.5) I doubt the magic smoke comes out but he won't be "getting out" far either. If his "truck" is a real one (breaker good buddy size) and he has 8-9' from mirror to mirror the best antenna is the co phasers you see on big rigs. Otherwise it is hard to beat a bottom coil loaded ~48" antenna right in the center of the roof. That is what I had on my van but you had to remember to take off the vertical when you went into a parking garage. ;-) I completely missed that it was a CB radio he was talking about. Thought he was talking about a new VHF Marine radio. But the antenna issues remain the same. For max range whatever antenna he uses needs to be of the proper length. At 27 MHz a full wavelength is about 103 inches. A half wave antenna would be about 51.5 inches long and aquarter wave length antenna would therefore be about 25.75 inches. If really anal about these things, an SWR meter should then used to trim the antenna length to the lowest SWR on channel 20 (mid-range). I have an old SWR meter from the CB craze years that I never use anymore but for some reason it's one of those things I just can't throw away. I have one for my marine VHF. Have not used it in years. Actually I am looking at a new radio for the boat. One with AIS. Maybe Santa Clause. My wife has her phone. That is all we need ;-) Worst case I call a tow pirate but I have plenty of neighbors who owe me a tow. Sinking is not an issue, we will just wade ashore, I will plot a course through the mangroves with my aerial photos and boy scout compass and we will walk home. I do have loppers on the boat ;-) We get fog, and lots of ship traffic in SF Bay and slightly offshore. Would be nice to know what is coming. That is RADAR, a little overkill on a 20' pontoon don't you think? I doubt I will see that much ship traffic in the Estero Bay anyway, unless they can run in 2-3' of water. We have been socked in with fog tho. My wife thought it was so cool. I was navigating with aerial photos, a compass and the shapes of the edges of the mangroves. We did fine. I can run in a foot of water. But a 21’ boat is not really a radar platform. As to radar, I screwed up about 50 years ago, not getting a license with radar endorsement. Friend took care of the police radars, great side business. I spent 3 years fixing airborne transport radars. I get the idea that police RADARs are like Bic lighters. Other than calibrating them I imagine they get thrown away if they break. Electronics these days doesn't really break that much ... why I retired. This was when we still fixed boards. Would have made a nice pile of money as a side job. |
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#46
posted to rec.boats
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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 |
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#47
posted to rec.boats
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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 |
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