What Does 75 Meters Look Like?

[WA1GFZ]

I heard you can pick up an 8753D network analyzer used for about $7K
another fine tool. Used one this morning.

[Glenn K2KL]

Champion of the sky covered in maple syrup!!

It's a Hallicrafters S-20R with the very rare SooperDooperSpectrumScope option, and an outside speaker.  

Either that or an Agilent 89600 VSA.

73 John

[W1IA]

Glad you boyz liked that. It's a different and really cool way to look at the spectrum or a signal. The spectrogram I posted is but one of many ways of "viewing" a signal with the analyzer I used. I can also show instantaneous phase, PSD, PDF, amplitude (more or less what you would see on an oscilloscope) and more. It can show one or all of these simultaneously. Neat stuff.

JN did a great job explaining the image. The URL below is another shot I made of Brent, W1IA on 3 April. He had just put his new Class E rig back on the air after blowing it up the previous night. The shot shows the spectrum 10 kHz above and 10 kHz below Brent's center frequency, so there is much more detail of the AM signal on this shot.

Same as before, if you get a 404 Error, just hit reload.

Enjoy!

http://www.amwindow.org/misc/gif/w1ia75m3apr05annotated.gif

Wow!! Thanks Steve...This is great!! I was going to bring an analyzer to do a sweep on the rig, but you just saved me the time. The anti-aliasing filter is set to brick wall at 12.5 khz and the pic  proves it. YAY!!!

Thanks again guys...it fun to have the rig on the air.

Brent(Tina) W1IA

[w3jn]

new Class E rig back on the air after blowing it up the previous night

Was it spectacular, Brent?

Heard you and Keith last night on 90, sounds FB!

73 John

[WA1GFZ]

Yes Brent was strapping last night on 90 and sounded great!
K1BOY well strapped.

[W8ER]

Dave W9AD and I were oogling the display that Steve put up and Dave came up with this .. any guesses .. that is besides it's a display of WWV during the time announcement?




SDR-1000




$875 receiver only
$1375 100 watt transceiver

It does a 20 khz sweep. The picture of the screen was captured using a Logitec webcam. I understand it's a much better display in person.   :lol:

You can see the voice announcement, the click indicating the top of the minute and the first two tones following the click, I can't read the screen but it appears that they are less than 1 khz. I also see the calibrated signal strength reading (in dbm).

--Larry W8ER

[Steve - WB3HUZ]

That's pretty good frequency resolution on that display Larry. Do you know how fast it scans the 20 kHz segment?

Here's another shot taken tonight of K1JJ, W3DUQ, W2INR, W2APR and WB8BIL in QSO on 3880 kHz around 0030Z.

http://www.amwindow.org/misc/gif/jjduqinrapebil388011apr05annotated.gif

[W8ER]

That's pretty good frequency resolution on that display Larry. Do you know how fast it scans the 20 kHz segment?

Here's another shot taken tonight of K1JJ, W3DUQ, W2INR, W2APR and WB8BIL in QSO on 3880 kHz around 0030Z.

http://www.amwindow.org/misc/gif/jjduqinrapebil388011apr05annotated.gif

Actually I don't Steve. I assume that you are asking about the time it takes for a left to right traverse of the display. I am on the verge of ordering one of these things. Dave loves his, enough to displace his MarkV and his RX340, and I'm blown away by what I see. Since much is defined by software, I would think that some of the parameters involved might easily be changed to include wider sweeps .. etc .. to the limits of the hardware. Dave is saying that the SDR-1000 is a big improvement over the RX-340 in terms of recovered audio, selectivity, sync detector and I've heard MP3's to back that up! Additionally it just happens to include a transmitter! The guys at flex-radio have included routines that make the radio do AM and from what I have seen and heard of that .. incredible! A brickwall filter that allows you to set bandwidth out to 20 khz. I am seeing claims on the ultimate rejection of the filter being in the area of 50 db. I have seen some of Daves testing that shows it at about 40 db. I'll post more on this after I get mine and get some hands on time with it.

BTW great shot of the 75 meter activity. I heard you and the INR a bit earlier on 3880 but didn't stay around long enough to hear the rest jump in.

--Larry W8ER

[Steve - WB3HUZ]

The Flex Radio looks pretty cool, especially the RX side. I was surprised by the IMD specs of the TX side shown in April's QST - only -29 dB! That seems like a big step backwards considering radios with tube finals produced years and even decades ago produce IMD numbers of -40 dB or better.

[WA1GFZ]

Man I would love to see the hlr sbe rig in action.

[WD8BIL]

That's pretty neat Steve. Not only can I see the Junkston 122 VFO drift but the color at the carrier shows the fading real well!!

Neat schtuff !

[w3jn]

I can see everyone's on the same frequency, caw mawn...

If the ARRL gets their way with the bandwidth limitations every ham's gonna hafta buy one of these to make sure they're not too wide.

73 John

[WD8BIL]

.....to make sure they're not too wide.

How wide I am is none of their business !!!

Unless, of course, they're paying my food bills !!!   :lol:

[K1JJ]

Hmmmm....   I'm looking at that 10kc++ audio spike and wondering who or what was causing that!

It looks like the labeled stations are cleared leaving -  DUQ and me... :lol:

At first I thought it looked like a classic key-up spike, but it now looks to appear in the middle of a transmission when it happens, like an intermitant audio parasitic or something..  Any opinions?

I was running my class E rig and have axed Steve to take a close look at my sig when he gets a chance.  It may be nothing, but who knows...   This kind of thing can blow rigs up, so worth finding who is the source and get it fixed.

This reminds me that it might be a good thing for everyone to check their own "key up" transcient. That is something most of us have  never looked at and it is certainly part of our overall signal on AM.  I don't see anything here unusual, like spikes on the scope during key-up, just a sloped CW leading edge. I think a key-up square wave with a sharp leading edge would cause a spike. Just like CW, a tapered slope to the carrier on key up is the best idea to reduce spikes/key clicks.  [and check "un-key" for a nice sloping collapse too, otherwise our channel neighbors will be hearing lots of mysterious clicks during fast break in operation... :badgrin: ]

T

[W2VW]

I can see everyone's on the same frequency, caw mawn...
 

73 John

My channel selector has a loose set screw.

[W2VW]

Hmmmm....   I'm looking at that 10kc++ audio spike and wondering who or what was causing that!

It looks like the labeled stations are cleared leaving -  DUQ and me... :lol:


T

 

I have a lot of stuff to A/B for next time.

[K1JJ]

Whew.....   I just did a test with the guys on 75M and they hear no key up/down clicks nor audio spikes up the band. Guess my E rig is OK.

During the test other guys checked their rigs and we found one that had a little problem with key-up spikes. So it's worth the effort to check ourselves out.

Slow the o'scope sweep speed way down and occassionally the leading edge or trailing edge will appear when the rig is keyed. A classic smooth CW shaped edge is what you want to see for a clean signature.

T

[w3jn]

It was probably Bill's chair, T.  Actually it looks like it happened during Gary's transmission, but it if you look closely it appears to go completely across the screen which would lead me to believe it is some kind of broadband noise (lightning crash, electric fence, etc) rather than an audio spike.  Certainly doesn't really look like a parasitic.

Dave, are you sure that your channel selector's the only piece of equipment in your shack with a loose screw   ?

I have one of these instruments on my desk but no HF antenner, unfortunately  

73 John

[WA1GFZ]

You guys can get the same display if you down convert your IF to 12 KHz or so kHZ and use free SDR software.

[Art]

fine looking rig Larry . . .  

[w3jn]

You can't get 36 MHz of instantaneous bandwidth with a 12 KHz IF, though!

[WA1GFZ]

Everything has a price.

[Steve - WB3HUZ]

You won't even get a 20 kHz view (instantaneous or otherwise) using the sound card and the SDR software.

Tom:

I think the "spike" you see is legitimate. My guess is that it was an "s" or "h" sound and is just showing the excellent high frequency response of the transmitter. Now, if both you and Bill are lowpassing your audio at something less than 10 kHz, then there may be a problem.

[W2VW]

Dave, are you sure that your channel selector's the only piece of equipment in your shack with a loose screw   ?
73 John

Is this question meant to be rhetorical?

[W8ER]

You won't even get a 20 kHz view (instantaneous or otherwise) using the sound card and the SDR software.

Steve .. what am I seeing then on the SDR waterfall display? If you carefully look at the scale it looks as if the window is 10 khz either side of the center frequency. A little interpolation makes it appear that the scan may go out to 9 khz, either side, or a total of 18 khz. That's not far from a 20 khz view!

Art,

I am grilling Dave on his and thinking very seriously about one. They appear to be pretty impressive, especially the receiver. Steve pointed out the 3rd order IMD product was measured at only 29 db down by the ARRL Lab and I didn't notice that earlier. That is certainly NOT impressive. I notice that there is a lot of experimentation going on now with different sound cards, ones with higher sample rates like the m-audio card.  I do not know what sound card the ARRL used although I assume it was the Turtle Beach Santa Cruz.

How is yours doing? Have you been using it on AM?

--Larry