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eHam Forums / QRP / RE: WHEN IS QRP NOT QRP?
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on: April 21, 2013, 12:44:16 AM
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I agree, the big thing with the manpack operation is the use of less than optimal antennas - short whips or improvised dipoles.
As an apartment dweller, I emphasize with them : an FT817 into a 12' whip or magnetic loop is not a recipe for reliable communications.
To level the playing field, perhaps QRP should be 5W ERP.
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eHam Forums / Satellites / RE: Feasibility of making 2 way contacts to a space ship on trajectory to Mars?
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on: March 16, 2013, 12:06:37 AM
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Brilliant question: "I've just picked up a fault in the AE35 unit. It's going to go 100% failure in 72 hours." ..... "Roger your plan to go EVA and replace Alpha-Echo three-five unit prior to faliure." I think the store forwarding of messages will be the way to go - well done Mr Clarke. How much ERP will be needed to give them enough bandwidth to run Netflix to pass the time  |
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eHam Forums / HomeBrew / RE: Essential Components
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on: August 03, 2012, 07:20:41 PM
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Go to eBay, do a search on "diodes", "resistors", electrolytics", "disk capacitors", etc. You will find a number of China sources for these parts (usually called "kits").
Not sure that that's a risk I would take just to save a few $. Counterfeit / liberated parts that do not live up to their marked specs e.g. working voltage are a serious industry wide problem and despite the best vetting even find their way into military equipment. |
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eHam Forums / Misc / RE: Radio Shack Corp "Suspends" Dividend. Stock Crashes
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on: July 29, 2012, 10:20:09 AM
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As an armchair CEO, they should look at the British Maplin stores as a 'how to survive in electronics retailing' model: Very similar target audience but they did not fall into the cellphone trap. http://www.maplin.co.uk/home.aspxJust enough component choice for casual one day projects. Then more general stuff for Hams, experimenters, music band electronics and computer upgrades. Perhaps another key difference is store density - they stick to one store per major urban center - not every mall in every town. |
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eHam Forums / Elmers / RE: Need tight filter for 144.39
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on: July 25, 2012, 07:03:23 PM
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Perhaps you are going about it the wrong way looking for band pass filters:
Coax T stub notches could very well do it - and are cheap to try.
On the APRS RX you want a try a 1/4 wave open stub (or a pair 1/8 wave apart ) tuned to around 146.5 (and 147.5 MHz).
On the voice TX you want a single 1/4 wave stub tuned for 144.39 MHz.
The RX notche(s) kill the main voice carrier and the TX notch clears a hole in otherwise raised noise floor.
Just remember not to TX much below 146MHz.
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eHam Forums / Mobile Ham / RE: Yaesu FT-1900R vs FT-2900R
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on: July 15, 2012, 11:23:22 AM
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Thanks for the response, but I think you lost me. I am not really sure if you are saying this is a negative or plus for the 1900.
Pro 2900: 55w vs 75w may only be 1.3dB but for only $15 extra, if you need fringe coverage, why not. |
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eHam Forums / Mobile Ham / RE: Yaesu FT-1900R vs FT-2900R
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on: July 14, 2012, 09:29:59 PM
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I've also observed that the 1900 can outhear its tx range. IMHO, I don't think the receive specs between the two radios really amounts to much real world difference, and both radios hear quit well.
It's not uncommon for repeater receivers to have a noise floor that is degraded by the far out phase noise of co-sited transmitters ( or their own if the duplexer isolation is lacking ). In this situation more uplink power can help. |
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eHam Forums / Software Defined Radio / RE: SDR of the future
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on: July 11, 2012, 11:27:34 PM
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Well I actually have an all HF bands digital cartesian loop transmitter on my test bench!
The trick is to keep the total group delay around the decimate/interpolate->DA->Filter->Power amp->Filter->AD loop small compared to the period of the highest pole in your loop filter, this requires that the loop be closed at a sample rate of a few Mhz for a 50Khz loop bandwidth, sufficient to attenuate the IMD out to the 11th order for an SSB transmission. Not really a problem in a decent FPGA.
In fact most of the RX path can be reused to close the loop, it needs a separate NCO so the phase can be adjusted between tx and rx paths, and the loop gets closed a few stages up the CIC chains to keep the total group delay acceptable.
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At some point I must finish this project and do a proper writeup, but you know how projects are.... Always another cool idea to try out!
73 M0HCN
That is an impressive project. I would very much like to be reading about it one day - not just the hardware but also the VHDL/Verilog. |
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