longjohn119

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  1. The Mississippi River finally dropped to near normal levels so I got a chance to try this out 'on the water' fed to my Lowrance Elite 7 Ti through a RS-422 converter and then the AIS, GPS, as well as depth and water temp data are sent out the Elite TI via the built in WiFi (NMEA 0183 over Ethernet) to my Windows tablet running OpenCPN and other mapping software. I was getting approx. 7 miles range upstream and 7 miles range downstream which is on par, maybe slightly better than voice communications with a Marine Band radio when it was hooked up to the same antenna. Since it's mounted on the rear deck of a modified Jon boat the base of the antenna (1/4 wave vertical) is only a couple of feet above the water level which is the main limiter for range. Still 'seeing' a barge 7 miles out that is only moving 4-7 Mph gives me plenty of warning (At least an hour) and suits my main purpose perfectly. Also as I suspected the noise levels went up about 4 db with the 1/4 vertical over vertical 1/2 wave dipole I have at home although in practice I didn't notice any adverse affects.
  2. Initial test results dAISy Hat with an FT232 RS232 convert - Half wave vertical dipole at approx 30 ft fed with 80 ft 75 ohm RG-6 quad shield with balun at feed point (The mismatch is largely irrelevant in modern active front end **receivers**, transmitters are a different ballgame altogether) Noise, no Antenna = -126 dbm Noise with antenna = -123 dbm Results from 800+ messages: Minimum received signals = -117 dbm Maximum received signal = --67 dbm Average received signal = -91 dbm NOTES: (1) The more than acceptable 3db increase in noise from the antenna is mainly due to using quality coax and a vertical dipole with a proper balun which is a balanced antenna and tends to work more with the magnetic portion of the electromagnetic signal. A 1/4 wave vertical ground plane antenna would likely add another 3 - 6 db to the noise levels because it is an unbalanced antenna that works mainly with the electro (voltage) part of the electromagnetic signal and thus is more sensitive to RFI noise. Another engineering term for a vertical ground plane antenna is a Voltage Probe Antenna. However on most vessels a 1/4 to 5/8 wave vertical will be used since they are shorter (1/4) and/or are end fed rather than in the middle making them much easier to mount and feed on most smaller vessels. (2) While this could benefit from a 10 db preamp with input and output filters and scaling one of the 2 meter amatuer band designs would be relatively simple, trying to get there with only 5 volts is tough as most are designed for 12-14V. Plus you are going to need to use fairly large air coil or a slug tuned ferrite coils (like in IF circuits) which have a higher Q and thus lower loss. filters using SMT inductors while convenient and small are inherently low Q and lossy and that is why everyone is getting poor results putting a preamp with SMT filters in front of these. No preamp will increase the SNR of a receiver only increase it as they will amplify both the noise and the signal present on the input in equal amounts. The only way to lower noise is by decreasing the input bandwidth and filtering out the noise before it reaches the input to the preamp. (3) My receive range roughly tripled over a RTL dongle and doubled compared to a HackRF SDR. This is most likely due to the poor dynamic range and SNR of the 8 bit ADCs even in the otherwise well designed HackRF Now it's off to mate this with my boat's GPS and the output to a RS-422 converter so I can add it and the GPS to my Lowrance Elite 7 Ti NMEA inputs and I can give it on on the water test this weekend .......
  3. Sorry about being a little slow to acknowledge, we got hit by one of those Global Warming enhanced extreme rain events Friday into Saturday morning and my basement took on a little water but luckily no real damage other than wet indoor/outdoor carpeting I have in my workshop and computer room. Just to add insult to injury we are going back above flood stage for the second time this summer so I won't be getting out on the river for a couple of weeks at least anyway and there is not a lot of AIS traffic at the 500 acre new lake I'm depth mapping. However I do need to get this going as I'm having my house sided in a month and I have to take down my antennas and I don't think I'll be putting that one back up (2 stacked vertical dipoles) because line of sight issues limits my range and this part of the Mississippi River is already well covered on MarineTraffic. I do however sit 6 blocks from the river right above a lock and dam that also happens to be district headquarters for the Corps of Engineers so I do get a lot of traffic for testing. Since last year I run everything at 38400 baud since my GPS has 10 hz output with the exception of the Garmin "Intelliducer" on my aquabot (Be sure to check that out on my blog, I just finished Version 2 a month ago) which is fixed at 4800 in but is bumped up to 38400 like the GPS when it is multiplexed and sent out the USB and Bluetooth outputs with the position data. It's also nice to have that I2C port just to make for an easier and better looking assembly for the Enviro pHat
  4. Proud new owner of a dAISy hat here. When I first saw the little USB unit a little over a year ago I thought is was just another reworked DVB tuner and baseband video ADC setup with a micro built in to control it. Obviously it's not that on further examination and when I saw the true 2 channel Raspi hat I just had to have one so I ordered one late Friday night and was pleasantly surprised that it had already arrived on Monday with my mail. Extra bonus points for customer service, I didn't even expect the order to be processed until Monday much less already be in my mailbox. The shipping was more than reasonable However I do have a couple of questions ..... First am I correct in concluding that I could just hook this to one of my FT232 devices or even to an Arduino (with RX level shifter) and control/test the radio? That would make it easier to test and to set up without have to do a setup on Raspi. Plus I could easily work it into an existing box by hooking the GPS to port 2 and hooking the output of the dAISy to where the GPS was hooked up. Basically I have a box with an Arduino Mega that used to be a multiplexer/logger but is a convenient way to route the GPS signal to different devices. Basically it reads my NEO-M8N and routes it out the USB, to an RS-422/485 level converter and to my Lowrance Elite TI and to a Bluetooth radio (HC-6). The finder itself can use AIS sentences and plot ships (Actually in my case barges on the Upper Mississippi River) The Elite TI then outputs the the position and depth (and AIS ) over the built-in WiFi to my Windows tablet. I use this setup to do depth mapping and sidescans of lakes and also interesting structure and wing dams on the Mississippi River and this is the way I get live data to my tablet since all my depth mapping software is Windows based. The AIS data however is only used on the Mississippi River but especially in late July through the end of September when I do a lot of fishing for Flathead Catfish and occasionally Walleye off the tips of wingdams and channel edge dropoffs. It's nice to have 15-20 minutes of advance notice so I can pull up my anchors and get out of the way (and the wake) of these monsters that can easily swamp a 1648 jon boat. I've been using the Marine Traffic app on my phone but you can't leave it running all the time or the data charges will kill you. I bought this for a system I'll build over the winter in the off season but if I can make this work in my existing setup this year would sure be nice The second question is about the I2C port, this will eventually go on a Raspi 3 with a Pimoroni Enviro pHat mounted in a Stevenson Screen which will supply temp and pressure (Converted to an MDA sentence in the Pi) as well as a tilt compensated Heading which along with the GPS and AIS data and will be sent out to my Tablet via WiFi and to my Elite Ti via a RS422/485 USB converter. Am I correct in concluding that the I2C port on the dAISy hat is just a feed through to the Pi and not even hooked to the circuitry of the radio? If so I can just hook the Enviro pHat right to that and not have to hack and tack wires to the Pi and dAISy hat which will be mounted just below the Stevenson shield. While it hasn't been updated in a year and my boat and systems are always in a constant state of flux you can see my boat setup on my blog The Netbook2Chartplotter Project