SmartSDR & 6300

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Received the 6300 a few days ago. I'm brand new to SDR radios. The 6300 installed very smoothly and was up and running in no time. Certainly is a big change from my Kenwood TS-590. Although in a "Shoot out" on 40 meters I'd have to say that the TS-590 receiver seems slightly more sensitive, with a little better signal to noise ratio.

I've been learning SmartSDR and I do have a question about it. It seems like there isn't very good control of the RF gain and the AGC on the receiver using SmartSDR? The only controls that I see for these functions is in the receiver panel on the right side of the screen there is a selection for "Fast, Med, Slow, Off" .....I assume that is the AGC control? if so, don't really see much difference when selecting these ??? There is a slider control next to that which seems to control the RF gain?? Doesn't seem to work very well controlling the RF gain of the receiver. Also I don't see any kind of selectable attenuator for the receiver front end? All of these controls are something I'm looking for to make the radio more "Listenable" and reduce the noise and static when listening to the receiver. The bands have not been very good lately and noise levels are high, this seems very hard to deal with, with the 6300 and SmartSDR.  Am I missing something here?
Thanks for any help. W6BWS - Bill



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K6NOK- Bill

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Posted 4 years ago

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Dale KB5VE

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Ok you will not see the big difference with fast,med and slow Agc as conventional radios because the reciever in the sdr does not experience the overload you get with a conventional reciever. As far as ATTand pream you have them in your left Side flag that pops out. But the real control is the Agc threashold, now there is the secret of many very good receivers. Adjust it to the noise floor and watch a signal in the noise come out.
(Edited)
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KD8TVB

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Dale, new flex 6300 here as well, can you elaborate on AGC threshold technique? Thanks, Howard
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W5XZ - dan

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switch the antenna to a dummy load; turn down AGCT (rf gain for old timers) until you just barely hear noise; switch back to a real antenna

73, w5xz, dan
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Steve N4LQ

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The technique is to adjust the AGC slider just high enough that you can hear band noise. Going further is not productive. If you want to hear some real AGC action then crank up the AGC slider fully to the right and scan through fast, med and slow on a CW signal. You'll hear a major difference in them. Fast will sound horrible, as it should. Slow will allow the AGC to take effect and smooth things out. With the slider to the left AGC isn't doing much because the threshold has been reduced. All in all it acts much like the old fashion RF Gain control except for the S meter which doesn't seem to know the difference :*)
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Robbie - KI4TTZ

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I learned that trick by watching a youtube video a while back (sorry I don't have the link).  I haven't used it (or needed it) much with the Flex but I tried it with another brand radio and it was amazing how the voice would come out when the noise level would drop.  I tried explaining it to some other hams and they thought I was crazy.  I view it as just another tool in the toolbox when trying to dig out a signal.
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W5XZ - dan

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but SOME  people like 'fast'...digging for weak signals in the noise...med & slow are for ssb guys, i think..
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KD8TVB

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Thank you for the comments, thanks to Bill for asking the question
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Dale KB5VE

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I did not answer since the answers were correct. I would like to note there is a difference in controlling the Agc threashold and using a rf gain. The Agc threashold never changes the sensatiivity of the reciever while rf gain does. As long as you have strong signals the rf gain is ok but you will never pull a weak signal out of the noise floor using rf gain to quiten the receive but you can with Agc threashold adjustment. The tentec Orion I had was great when you adjusted the Agc threashold. Correctly.
(Edited)
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Robbie - KI4TTZ

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Actually now that you mention it, I think the RF gain is what I was talking about.  Been a long week at work, so my brain is fried right now.  And honestly I don't know the technical differences between RF gain and AGC anyway but I'll have to research that another day.  (I'm just an amateur) ;-)
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K6NOK- Bill

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Lots of great information! Thank you all so much. I'm going to look at YouTube more closely and see if there maybe be some SmartSDR operating tips on there also.

Dale (KB5VE) you mentioned "ATT and Preamp" in the left side flag. I don't see those there at all on my SmartSDR .....perhaps SmartSDR doesn't offer those options on the 6300??? I do find "RF Gain" on the "ANT" tab of the left side flag. However, when I try to adjust it it doesn't move linearly, it seems to only go to maximum (20) or minimum (0)....nothing in between. Even at minimum (0) I don't hear (or see) any discernible difference in receive levels or noise.

Sorry to seem so dense folks, but this SDR is a whole new world that is going to take some getting used to for me. :)
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Steve N4LQ

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Like I said....RF Gain doesn't work with the 6300. There is no preamp therefore the slider slideth not.
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Lee, Elmer

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Actually there is a 20 dB preamp.  It reduces its gain as the freq reduces being highest on 6.  Its control is either off (left) or on (right)

73  W9OY
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Dale KB5VE

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Lee one thing that is comming out the 6300 has many less features than the 6500 and the 6700. Much like the sdr 1500. I am sure it is a very good radio next to the radios it was designed to compete with. It is a shame we cannot do a demo of each radio as we do in power sdr but as I see it it cannot happen because the smart sdr is client software and does not know the results of the movements of its controls. Maybe in the future Flex will have a detailed video of all it's radios to show you the differences in the units.

Also do understand with flex being a direct sampling radio you will always see the same smeter , -DBMS readings even if you turn a preamp on. I love this feature and even power sdr has this feature. Changes in Agc, Agc threashold, attenuation , preamps and rf gain are not shown on the panadapter . Yes there is a learning curve and a good buddy who know how to use these features is very handy. I love the community but many of us have regular sheds to just talk the good, the bad and the needy of the flex 6000. That is what ham radio is all about. This is a great platform and I believe it will become a game changer in all aspects of the radio in the future. The buddy system is a great way to get totally up to snuff with this platform.
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Dave - WB5NHL

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One other thing to remember is that the RF Gain control in convention receivers is designed to control input overload and resulting spurious responses. With a direct sampling SDR, overload is much more difficult and (as Steve has explained) primarily occurs with VERY large signals on the input to the A/D converter.
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Lee, Elmer

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AGC-T sets the point where the AGC starts to automatically reduce gain in the system.  It is not RF gain.  It tunes the radio to a given noise environment.  Before the AGC starts to work is when your radio is most sensitive.  As soon as AGC starts the sensitivity is dynamically reduced by a feedback loop.  AGC however saves your ears if there is a sudden strong signal occurrence.  Remember these are dB so they are multiples of strength not just linear.  With a weak signal you do not want the AGC engaged so you can hear with most sensitivity right at the band noise.  This is why signals seem to pop out of the noise, because the AGC feedback is not cutting them down.  

The way you set AGC-T is to find a quiet part of the band with the antenna connected and listen to the noise and reduce AGC-T until the noise is nearly quiet.  Since you can't really listen under the noise, that point is the practical limit of any signal you can copy.  If the noise is S3 your not going to copy a S1 signal so set your receivers limit of sensitivity to S3 and it will enhance your chances of hearing that S2.9 signal that just keeps popping its head out of the noise.  You may have to fiddle a bit finding the sweet spot but this is the best first iteration. Setting AGC-T also gives you the widest dynamic range performance.  Persistence is OK but you should really take a second and tune your AGC-T every time you turn on your receiver as atmospherics and local noise vary day to day and even within the day.  My AGC-T is at a different level at high noon on 40M than at midnight on the same band so I adjust accordingly.  I even use the choice for AGC-T in the FlexControl since it makes tuning a breeze and can make a difference when trying to get every last dB on a super weak signal.

73  W9OY 
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Steve N4LQ

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What is AGC-T really doing? When you slide it to the left, the receiver goes totally mute. Normal receivers make more noise when the threshold is reduced, not less. I'm just trying to understand what this really is.
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Dale KB5VE

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Great post. One thing people have to understand is the noise floor you see in the panadapter in not a flat line no mater how straight it looks. There are peaks and valleys between the peaks. When you bring the threashold down to the minimum , just as you stated that is the point of most sensatiivity and yes sometimes these signals pop out of nowhere, but that is not true they were in the valleys. I am not technical but have operated for over 45 years with many receivers and transceivers many of which had the means to set the Agc threashold even in receivers made in the 60's it just was not called this.

Also this is not just a flex secret there are several radios out there you can do this with. The fact is flex has made this a major part of the reciever operation and has not hid it in menues and sub menues.

If you want to have some fun turn the amplifier off and but the mic and key on the shelf and just use your 6000 as a swl receiver, but be careful you can get hooked there is a lot of stuff out there.

Happy Flexing!
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Lee, Elmer

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Dale 

Designing this radio must have been a labor of love.  How do you take a robust system and cut out enough stuff to save a couple thousand dollars but not totally hose the radio's performance, that is the design problem.  In my opinion Flex solved that design problem in spades clubs and diamonds.  There are some compromises like the antenna switch is very simple compared to the other radios, and no pre-selector, and no balanced input, only 2 panadapters, etc etc but the compromises in the main do not really effect the performance of the radio.  My filters are just as good, my CW performance is just as good, I have pro-audio it's just single ended not balanced, in fact with this radio I have the best articulated audio I've ever had.  CW is as good as any Ten Tec I ever owned.  I look every day for a situation where the radio signal handling crunches and I have yet to find that occurrence even when transmitting 50W on a vertical 175 ft away from my receive vertical on the same band.  In that instance my receive capability was limited not by the receiver but by the non Flex transmitter's cleanliness. While transmitting one one antenna I was able to copy stations at -105 dBm a few dozen khz up the band on the 6300 once I got away from the sideband noise of the other transmitter.  (this is why those receiver signal generators cost an arm and a leg)   If I was able to muster 1500W from the other transmitter I would have tried that and I still don't think the radio would have crunched though it might be pushing the envelop.  One of these days I will set up something to give this a try.  The features are there they just are not there in excess abundance and you have to take a little time to figure out how to maximize the radios performance.  It connects to all of my favorite peripheral programs like skimmer, writelog, ddutil and dxlab without a hitch.  The software continues to improve in both features and performance for example witness the new processor, a HUGE advance in performance.  Also it gives the average ham the choice.  Do you want to save up a little more money to get the added features of a 6500 or 6700 or do you just want to give SDR a whirl.  

73  W9OY

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Dale KB5VE

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I have owned all their radios in fact still have- 1500 and 3000 because they still have a place in my operations. The 6000 platform is a blank canvas which is just waiting to be filled with great features. It will take a while to do this. I have stayed loyal and having the two power sdr radios allow me to take advantage of power sdr features wich are not in smart sdr yet. I do not know a conventional radio that I would go to. When I get my new tower and log periodic up I will be able to really enjoy what it can do.

I do a lot of remote so the time table for remote has really been a tough nut to take. It fact I am on the gulf coast this week and in the past I would have been banging away on my flex but with no remote and my third 3000 not in line and qrp remote with the 1500 not my bag, I will wait and hope the Ssb remote comes sooner than later.

No I am not in love with my radio, God and my family occupy that spot but really like my flex yes,yes,yes. Will I really like it with remote over WAN , you bet! Still look forward to hitting the own switch each evening and seeing "DALEKB5VE pop up on my flex 6500.

Keep enjoying your flex.
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k0eoo

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I'm not sure I saw mention of what AGC-T is.  AGC-T stands for AGC Threshold or in some quarters its call  Delayed AGC.  Collins and most radios after the late 50's started using this type of AGC bacause it reduced the noise without reducing the recieved audio amplitude.  When you move the slider to the right you are lowering the threshold so the noise comes up and the opposite is true if you move the slider to the left you lower the noise but you'll notice the audio amplitude stays pretty much the same until you lower the AGC-T too much...  The action of AGC-T on the Flex compares very favorably to that on many of my Collins rigs, 75A4, KWM-2 and 51S-1 and so on...  AGC-T is the very best AGC design for reducing band noise without reducing received audio amplitude thereby reducing operating fatigue.
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k0eoo

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When you move the slider to the left you are increasing the threshold voltage that the signal has to overcome to be heard, that's why it gets quiet...  And moving the slider to the right reduces the threshold voltage so weak signals and noise can get through....  
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Steve N4LQ

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Then it's entirely different than for example the K3. No matter where you adjust the K3's threshold you still hear signals and band noise. It simply changes the strength of signal required to activate the AGC. Higher numbers mean a stronger signal is required to trigger AGC. Lower number kill the AGC thus more band noise is heard. It never mutes the receiver like the Flex. Whatever.....The Flex system is fine...Just different. Steve N4LQ
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Lee, Elmer

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The K3 is not really a software defined radio. It's a conventional radio with a software defined dongle on the output. Its basically the logical extension of the omni 5 from 35 years ago

73 W9OY
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Barry N1EU

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Other than a hardware protection circuit against s9++ signals overloading the ADC, the K3 AGC is entirely digital under firmware control.  In the matter under discussion it is not a "conventional" radio, but a software defined radio.  The K3 AGC is nothing like the Omni V AGC.
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Lee, Elmer

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Does the K3 send voltages to amplifiers to retard their gain? Are the filters in the AGC loop? Does the AGC in any way communicate with parts of the radio that are hardware? If the answer to any of these is yes then from a design perspective the radio is a conventional radio and you have drunk elecrafts marketing kool aid.

What I said was the K3 was the logical extension of the omni 5 design which was followed by the omni 6 then opt 1 then opt 2 then opt 3 then orion then orion 2 then K3. These radios share virtually the same topology. RF to intermediate stages of filtering and amplification to some kind of detector to some kind of post detector audio level like signal manipulation. If the radio was SDR it would not need a second true SDR like the lpan to control it.

73 W9OY
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Steve N4LQ

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OMG. My K3 saw that "dongle" comment. A big frown came upon its display and 3 knobs fell off. 73 N4LQ
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Lee, Elmer

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Three knobs fell off ... See what I mean ☺

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