The circuit, that is a little weak.
I have a VEC-8218 built from a kit and it is functional. Schematic here:
Uses a MRF901 front end with 1N270 detector. This is 1999 technology.
I would like to improve the ability to detect higher frequencies. The higher the better but good response at 2+ GHz would be a minimum.
Suggestions to circuit changes please.
Use a MMIC or two in the front end, and a schottky detector, or even better one of those RF log detector chips.
-- John Larkin Highland Technology Inc www.highlandtechnology.com jlarkin at highlandtechnology dot com Precision electronic instrumentation Picosecond-resolution Digital Delay and Pulse generators Custom timing and laser controllers Photonics and fiberoptic TTL data links VME analog, thermocouple, LVDT, synchro, tachometer Multichannel arbitrary waveform generators
Welcome to the 21th century.
Smart buggers would use 2.5GHz FH/DSS running below 0db. All you see is no ise, if you don't follow the proper FH/DSS protocol. I am using MRF24J40 t o communicate and scan for signals. Interesting enough, communications wor k at any level of signal and noise, even with the occasional pop-corn burst (huge signal from microwave).
Unfortunately they are out of business. Perhaps it shows up on ebay. They used an Analog Devices RF detector as the front end IIRC. I talked to the guy who designed it. He first started out just selling them at the ham flea markets.
Besides the meter (log or linear), it had a LED that goes off to detects bursts of RF.
I would call it early 1980's tech.
Put a jet engine in a Volkswagen, and the result is still a Volkswagen.
The problem with improving the sensitivity and bandwidth is that it will hear literally everything. Trying to detect a flea power bug under a mess of high power microwave, broadcast, and radar interference is not going to be easy. When you use a broadband amp to improve your desired frequency range and gain, you also amplifier the junk. You'll need to determine what frequency range you find interesting, filter the front end, and amplify only the range what you want to hear.
Replace the front end bipolar xsistor with a MMIC. They're cheap, easy to use, simple design, stable, >10dB gain, and
50/75 ohms in and out. Two caps, one choke, one resistor, and you're done. Rip out the bipolar amp, and replace it with a MMIC amp. (Incidentally, I had to do that with my Cushman CE-6a service monitor when I blew out the front end and found a replacement hybrid amp to be unobtainable).When you discover that you're picking up literally everything, put a filter in front of the MMIC amp. At 2.4GHz, various ceramic and cavity resonators are common. I made a few of these to make it easier for my handheld frequency counter to find the desired signal to count. If you plan to use yours on a mountain top infested with many transmitters, a filter and careful shielding is a necessity.
-- Jeff Liebermann jeffl@cruzio.com 150 Felker St #D http://www.LearnByDestroying.com Santa Cruz CA 95060 http://802.11junk.com Skype: JeffLiebermann AE6KS 831-336-2558
Naaaah! You get a VW that won't stay on the ground. A neighbor of mine, engineer at Air Research used an APU to do exactly that.
Besides the tendency to fly, it wasn't very fast... just squirrely.
Problem was solved by gearing down the turbine to a prop... then it was damned fast ;-) ...Jim Thompson
--
| James E.Thompson, CTO | mens |
| Analog Innovations, Inc. | et |
| Analog/Mixed-Signal ASIC's and Discrete Systems | manus |
| Phoenix, Arizona 85048 Skype: Contacts Only | |
| Voice:(480)460-2350 Fax: Available upon request | Brass Rat |
| E-mail Icon at http://www.analog-innovations.com | 1962 |
I love to cook with wine. Sometimes I even put it in the food.
This one? There are several, but I couldn't find one with a prop.
During the 1970's, I worked with a distracted engineer that made a high speed video of the inside of a running VW engine. He found that the pushrods bent at high RPM's, thus limiting the engine power. So, he diverted some of your tax dollars by having a friend at an aerospace company produce some titanium push rods. It worked and added plenty of extra RPM's. The problem was that the added power also broke other things in the drive train, mostly couplings and gears. Because of the risk of breakage, the RPM had to be limited resulting in fairly standard VW performance.
An optimum system is where everything limits out at the same place. In RF design, the maximum dynamic range is achieved when all of the various stages saturate or clip at a specific input level. Same with the VW, where every component of the drive train is expected to break at the same power/torque/RPM level. Add too much power in a VW drive chain, and something will break. Add too much gain in front of the receiver, and something will break further down the chain.
I don't know where the phrase originated, but I recall it was common in the late 1960's. When VW released the JETTA model in 1979, I suspected a connection, but never investigated. Officially, the various VW models were named after various winds, but I'm suspicious.
-- Jeff Liebermann jeffl@cruzio.com 150 Felker St #D http://www.LearnByDestroying.com Santa Cruz CA 95060 http://802.11junk.com Skype: JeffLiebermann AE6KS 831-336-2558
The guy's name was Bud Weaver, 1962-64 time-frame, when I lived on East Vernon in Old Town Scottsdale.
...Jim Thompson
--
| James E.Thompson, CTO | mens |
| Analog Innovations, Inc. | et |
| Analog/Mixed-Signal ASIC's and Discrete Systems | manus |
| Phoenix, Arizona 85048 Skype: Contacts Only | |
| Voice:(480)460-2350 Fax: Available upon request | Brass Rat |
| E-mail Icon at http://www.analog-innovations.com | 1962 |
I love to cook with wine. Sometimes I even put it in the food.
Maybe, maybe not. That depends a lot on the various system properties desired. You might want a front end that does not easily overload so that weaker signals can be found underneath, think about DSSS. There are other cases that i am sure you can find.
?-)
In the end, all analogies fall apart.
What methinks you're describing is desensitization. That's where a nearby but off frequency signal causes the receiver front end to rectify the RF, which causes the device(s) to either saturate or cutoff, thus reducing the sensitivity. Because it's fairly close to the receive frequency, front end RF filtering does help. Because it's not inside the IF bandwidth, AGC doesn't help.
For NBFM, the test uses a passive combiner at the antenna fed with 2 signal generators. One is set to the receive frequency and adjusted for 12dB SINAD. The other is unmodulated and set to a frequency outside the IF bandwidth, usually 1MHz away from the other generator. The unmodulated generator level is increased until the SINAD drops
1dB(???). Things are more complexicated with digital systems, but the basic idea is the same:The design problem is how much signal level can the RF and mixer stages, prior to first IF filter, handle before clipping. It's a measure of the power handling capability of the receiver front end. If the receiver is expected to handle XX milliwatts of RF shoved down the antenna cable, the front end should remain linear at that level. If one stage has too much or two little gain, the dynamic range will suffer. Too much gain, and something will clip early, causing the high end of the dynamic range to be reduced. Too little gain, and the sensitivity suffers, causing the low end of the dynamic range to increase. However, when all the stages limit out at the same RF input level, presumably one has the maximum dynamic range. Desense is a very real problem on crowded mountain top radio sites and on crowded vessel masts.
My analogy was in reference to the receiver gain distribution, without consideration for overload phenomenon (desense, blocking, IMD, etc), for which there is no analogous mechanism in the VW drive train.
-- Jeff Liebermann jeffl@cruzio.com 150 Felker St #D http://www.LearnByDestroying.com Santa Cruz CA 95060 http://802.11junk.com Skype: JeffLiebermann AE6KS 831-336-2558
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