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Messages - ThElectriCat

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Equipment / Re: 9:1 or 49:1 unun for end-fed long/random wire?
« on: October 19, 2019, 0624 UTC »
This may not be relevant to HF stuff, but the antenna I use for NDB reception has a 400:1 transformer (20:1) turns ratio. I have never tried to transmit through it, but it proved the optimal ratio for receiving with my setup.

Equipment / Re: Test Equipment for First Time Build
« on: September 25, 2019, 0406 UTC »
In the beginning, I wouldn't bother with a spectrum analyzer. 
I, begrudgingly, Agree
I lusted after one of those for a long time, I finally got one (an HP8594E) aaand...
I don't really use it anywhere below a few hundred MHz. I use my scope and frequency counter every day.

my recommended top three (after the usual electrinic stuff such as a multimeter, power supply etc) are;
1. oscilloscope (my preference is analog, but any good scope is good and some digital features are really nice)
2. frequency counter (a cheapie is probably sufficient)
3. signal source. (slightly less important for building transmitters, but good luck building or even fixing a receiver without one. of course a cheap analog one is fine if used with the frequency counter. )

hope this helps _

Equipment / Re: These Satellite Antennas Were Inspired by Origami
« on: September 25, 2019, 0400 UTC »
This looks as far as I can tell like a foldable version of an single element axial endfire helical antenna (just a helix if you are familiar with satellite communications.
Those are usually several wavelengths long and the greater part of a wavelength or so in all other dimensions.
        Nice wide bandwidth
        Tight beam of circularly polarized radiation
        Easy to match to 50 ohms with a flattened helix end
        Invented by John Kraus after a professor of his said "It will never work" (one does not stumble upon things this satisfying often)
        Ruining ones life by a mad, all consuming obsession to construct an antenna the size of a building and then figuring out how to point it as to work DX

Equipment / Re: 80M home brew Mag Loop VS. inverted L comparison
« on: September 25, 2019, 0352 UTC »
If you have both antennas, you may want to use the loop for RX, where its tuned, narrowband inherent characteristics and deep nulls will help to reduce interference from strong local stations.
Of course, for RX only, a much smaller, multiturn loop can be used if you are so inclined

Equipment / Re: 80M home brew Mag Loop VS. inverted L comparison
« on: September 24, 2019, 0310 UTC »
Nice work. Loops like these are always going to be lossy and bad for dx on the low bands,
this is true, but if you are interested in NVIS communications (Near Vertical Incidence Skywave), which is really good for shorter range HF communications, loops can be excellent performers.
there are lots of online resources on NVIS on ham websites for anyone who is unfamiliar.

probably going to get yelled at for mentioning my favorite receivers, but...
Watkins Johnson receivers, have s meters that are somewhere in between log and linear scale, and are extremely useful for setting the RF gain manually, but I am pretty sure thats what they are for. I can't really find a better way to use them. some of the clearest signals I can hear barely deflect them, and some of the worst do.

Equipment / Re: Filters For Dummies
« on: August 17, 2019, 1622 UTC »
One of the simplest FM filters which can be reasonably practical for the homebuilder are made from coax.
They rely on the fact that a quarter wave stub can either look like a short or an open circuit depending on whether it is open or shorted respectively. 
Get a coax tee, and connect a quarter wave of good quality coax to the tee solder the far end of it together (conductor and shield) and put the tee inline with your feedline.
This is, in fact, electrically very similar to a cavity filter, but with a little bit more loss and lower Q, but it is much cheaper and more homebrew friendly.

Remember that a quarter wave will be a normal quarter wave in free space multiplied by the velocity factor of your coax, which you should be able to look up (usually 0.6 to 0.8)

Make sure to include the length added by the coax tee and measure as accurately as possible.  A big advantage of these filters is that they are a short circuit at dc. When I worked in broadcast, I would put them in between the exciter (usually a 20 or so watt transmitter) and the 30 Kw power amplifer, that way DC spikes caused by transmitter problems wouldn't kill the solid state exciter. 

some things to be careful of.
make sure your transmitter is ac coupled, if the plate/collector/drain voltage is present on the output, this filter won't work
if you are transmitting more than a watt or so, hook up the filter and run it, make sure its not getting warm. if you have it cut for the wrong frequency, your transmitter will see a very bad vswr, and the filter will dissipate as much power as the loss in the coax allows.

Other / Re: Racist ramblings on 80m
« on: August 17, 2019, 1605 UTC »
I actually Have a ham license, but hardly ever use it for the same reasons. Don't get me wrong, when I used to be on the air all the time, I met lots of good people, but there's too much of an old boys club, eager to tell anyone new exactly how the best hams should do things, that combined with people like those in the original post, and a lack of desire to say "hello, where are you. OK goodbye!"  as the primary radio type of conversation, pushed me away from ham radio.
Most of the really interesting stuff is unlicensed anyway.

Other / Racist ramblings on 80m
« on: July 29, 2019, 0456 UTC »
wow, I have heard a surprising amount of recordings/shouting sessions on 80 meters, (currently 3908 Kc, 0454 utc, 7-28-19)
lots of sexual, anti semetic, anti/pro trump, pro rape, anti/pro religious and other dirty content
featuring callsigns which may or may not actually belong to the hams involved.
I have heard these significantly more in the last year or so.

Thats a really cool transmission method, (and an image worthy of broadcasting)
I have seen some of the C-MT and S-MT hell methods used for QRSS, but never anything that actually draws any image of high resolution or span in a waterfall.
Nick work!

WEFAX and SSTV / frequencies
« on: July 28, 2019, 0532 UTC »
Is it just me? or is the Honolulu Hawaii radiofax transmitter on 11090 Kc running 100 cycles low?

I am listening to all with a 1 Kc bandpass and a BFO 1.9 Kc below center frequency.
No other sites seem to deviate from their posted TX frequencies.

WEFAX and SSTV / Re: WEFAX software?
« on: July 27, 2019, 0132 UTC »
being cheap, I use FLdigi,(no offense Chris) it works pretty well for wefax, and it is free.
That being said, I use it on linux, I have used it on a MAC quite a while ago, and with no problems, but I have never used it with microsoft.

Longwave Loggings / Re: SDR Receivers Useful For MW/LW
« on: July 16, 2019, 0108 UTC »
I got the eval board, but just the one with clock, power, buffer, and IO, not the one with the fpga and software. That would probably already work as an sdr if one wanted it to, but the project is really the design of the data transfer and RF front end. The hardest part is getting the data off the ADC in an effecient and universally understood manner

Longwave Loggings / Re: SDR Receivers Useful For MW/LW
« on: July 11, 2019, 0247 UTC »
Thanks KaySeeks, both those articles are indeed useful.
I have some unique advantages (and disadvantages) from choosing the ad7760. its max output data rate is only 2.5 MSPS with an internal flow pass filter set to 1 MHz. the read rate is 5 MHz on a parallel bus.
This will certainly be nice for prototyping, as I might even get away with some bodge wires and standard probing techniques.
Of course, the receiver won't work above 1 Mhz, (undersampling really isn't an option with this part) But I decided to take the high frequency hit due to the relative abundance of good SDRs for hf and vhf frequencies, and the relative paucity of ones that work down to DC.
Heres hoping that a DC coupled 1 MHz receiver will be a hit with the www.vlf.it guys, NDB dxers, and all the rest of us down here in the mud

Longwave Loggings / Re: SDR Receivers Useful For MW/LW
« on: July 05, 2019, 0242 UTC »
I am currently working on a design that used the analog devices 7760 sigma delta ADC  for this purpose. 2.5 MSPS max rate will allow it to have a DC to 1 MHZ range.
I wont yet say when it will be ready, as I am encountering difficulty reliably getting the 24 bit samples off the adc in such a way as to send them over a network connection.
I am going to use a good layout with plent of shielding and a seperate isolated power supply for the analog front end.
The impetus for this project is mainly due to the lack of software defined radios which produce little enough noise to be used on longwave frequencies and have low noise signal chains.

of course, this project will e open source. schematics and code will be available when it is done.

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