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  #601 (permalink)  
Old 06-10-2013, 9:46 AM
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Kev70-

The basic concept being discussed when someone refers to impedance matching is energy transfer between a source and a load. A basic concept of physics is that maximum energy is transferred when the impedance (or internal resistance in the case of a DC source) of a source is the same as the impedance (or resistance in the case of a resistive load) of the load.

A very simple example is to model a battery connected to a resistive load. A battery can be modeled as a voltage source in series with a small resistor equivalent to the internal series resistance of the battery. For maximum power transfer to the load, the load resistance should be equal to internal series resistance of the battery. For external reference I give you the following:

Maximum power transfer theorem - Wikipedia, the free encyclopedia

In dealing with an antenna and a transmitter or receiver the same holds true. For maximum power transfer the impedance of the transmitter or receiver must be equal to the impedance of the antenna. This topic is mostly discussed in relation to a transmitter and an antenna since very bad things can happen to the transmitter if you don't have a match. You usually use an SWR (Standing Wave Ratio) meter to show you the relative degree of mismatch between the transmitter and the antenna. External reference:

Standing wave ratio - Wikipedia, the free encyclopedia

Since the transmitter generally has a fixed output impedance, typically 50 Ohms, it's frequently necessary to put an impedance matching device between the transmitter and the feedline/antenna. Coincidentally, when the impedance is matched between the transmitter and the antenna, it is also matched between the receiver and the antenna. This means that the maximum amount of power will be transferred between the antenna and the receiver, providing the best conditions for receiving. The background atmospheric noise (which has been stated IS a signal) and the transmitted signals will both appear loudest when the antenna is matched to the receiver. Generally speaking, matching can be achieved by one of two methods. The first method is to use a resonant antenna. This will provide excellent results a one or a couple of frequencies. The other is to use some kind of antenna tuner to match the antenna to the receiver / transmitter. This will provide the best results over a wide range of frequencies. (there are antennas which are broadband, such as a log-periodic Yagi, which are extremely broadband, also a discone, but I'm trying to cover the most ground with the minimum words)

An extremely useful tool for evaluating antennas and determining their impedance is a Noise Bridge, example:

MFJ Enterprises Inc.

I've used one for many years to evaluate antennas after they're installed. My present antenna consists of a large dipole antenna, sized by the maximum distance I could stretch between two large trees. I didn't even bother to measure the wire lengths, just laid out wire between the two trees and cut it in the middle. After the antenna was up, I used the noise bridge to tell me it was resonant at 1.4 MHz. It also told me the reactance at any arbitrary frequency of interest by adjusting the frequency of the noise bridge then reading off the results. I personally use the Autek Research RF ANALYST RF-1

AUTEK RESEARCH home page

because it is easier to use, being digital. I've used that specific model for about twenty years and find it to be adequate for all my needs, and totally trouble free.

I think the best advice is to read, learn, and come up with your own conclusions based on your experimentation. Keep a good notebook or journal. Write down all of the details of your experimental setup and what results you observed. Refer to it when making changes to your setup and record the newly observed results. The best general source for all this kind of information is the ARRL Handbook

ARRL :: Specials & Sales :: ARRL Handbook (2012 Softcover Edition)

If you don't feel like buying one, they have them in most public libraries.
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  #602 (permalink)  
Old 06-10-2013, 3:23 PM
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Quote:
Originally Posted by WB2KTG View Post
Coincidentally, when the impedance is matched between the transmitter and the antenna, it is also matched between the receiver and the antenna. This means that the maximum amount of power will be transferred between the antenna and the receiver, providing the best conditions for receiving. The background atmospheric noise (which has been stated IS a signal) and the transmitted signals will both appear loudest when the antenna is matched to the receiver.
So it's more of a win with transmission since you're wasting less power. With reception, it's not a win if it just raises the noise level.
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  #603 (permalink)  
Old 06-10-2013, 3:54 PM
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scowl-

It's more of a win with a transmitter because a poor match will really decrease the output power (or possibly damage) a solid state transmitter, can cause arcing in the shack and other 'strange' behavior.

With a receiver, you will always hear pretty much the same sounding background noise, either created by the radio itself or naturally occurring RF. With a really poor antenna, all you will hear is background noise. As somebody mentioned earlier on this site, a reasonable test for the quality of a radio receiver is to terminate the input with it's characteristic impedance, a carbon 50 Ohm resistor would work just fine. Listen to the speaker, or output the speaker signal to a spectrum analyzer or oscilloscope. Then remove the resistor and attach the antenna. Re-listen to the signal. In the higher frequencies let's say 12 - 30 MHz, if you hear an increase in noise level, you know your receiver is sensitive and quiet enough. You will NEVER have a case where JUST the noise level increases without an increase in signal level, if a signal is present. RF Noise is signal too. There is always an absolute signal to noise ratio. That number would be determined using a calibrated signal analyzer or RF voltmeter, or super-duper high quality receiver. A figure of merit for the CR-1 or any other non-ideal receiver would be how close the observed S/N ratio is to the absolute S/N. The difference between the two being the noise contribution of the receiver being evaluated.
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  #604 (permalink)  
Old 06-11-2013, 11:31 AM
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The other issue I don't think we've covered is using the shield of the coax to reduce local RFI with an unbalanced antenna. It seems simple to me: anything the shield picks up will be out of phase and cancelled out.

It can't be that simple, right? There's a reason why XLR (balanced) cables have two wires (+ and -) and a shield and are nearly perfect at cancelling out any noise they pick up between an input and an output.
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  #605 (permalink)  
Old 06-14-2013, 11:38 AM
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scowl-

When using a piece of coax with the shield grounded and the center conductor going to an unbalanced antenna, shield keeps the local RFI from getting into the center conductor by shielding it. The RFI causes the electrons in the shield to produce a current, which then is conducted into the ground and is dissipated. Since the majority of the RFI's energy was spent making the electrons in the shield move, there was less (or very much less) energy to make the electrons in the center conductor move.

With XLR cables, Ethernet cables, telephone cables, the 'secret sauce' here is to use a twisted pair rather than two straight parallel conductors. Since RFI will be induced pretty much equally into both wires, the result is a 'common mode' signal, meaning that the noise is common to both wires. Since difference signal in the output of the twisted pair is what is used by the device connected to it, the common mode signal is ignored, the differential signal is what is used. The addition of a shield to typical XLR cable makes the situation 'more better' than the twisted pair alone.

When you have an RF signal flowing through a coax, like between a transmitter and an antenna (or between an antenna and a receiver) the electric field is mostly (just about all) constrained to stay within the dielectric between the center conductor and the inside of the shield, preventing radiation from the feedline.
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  #606 (permalink)  
Old 06-15-2013, 1:34 PM
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Default CR1 back

Hi all,I received my CR1 back from commradio last week and have been doing alot of listening. They corrected the frequency calibration and now it is spot on! turn around was only 1 day in their shop plus the time to ship. Had it back in 4 days! Nice service. I have been using it on my deck and trying different portable setups with whips and such. I have found the perfect portable small setup for me. I use my miracle antenna and connect it directly to the antenna input on my MFJ 1020c. I can use the bypass switch so the antenna just passes thru the 1020 and can tune the whip as normal. If I need a little boost, I just tune the whip first and then un bypass the mfj and tune it as well. Works great and I can throw it in a small bag and off I go! Great little radio. I am very happy and look forward to the july updates. Dion
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  #607 (permalink)  
Old 06-15-2013, 11:14 PM
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It would be nice to read about what the July update will fix an/or add to the CR-1.
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  #608 (permalink)  
Old 06-17-2013, 9:45 AM
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NRD-505

If you could call the shots, what would YOU fix and/or add to the CR-1?
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  #609 (permalink)  
Old 06-17-2013, 11:04 AM
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I'm on the fence about this little radio, everything looks fantastic.

But the one thing that would seal the deal for me is if the coverage went beyond 260mhz up to 380mhz so the whole military aircraft UHF specturm would be included.

I wouldn't even bring it up unless the radio didn't already go up to 260mhz.
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  #610 (permalink)  
Old 06-17-2013, 11:24 AM
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If you're looking for an easily tunable VHF/UHF receiver, the CR-1 is not what you want at least with the present firmware. Tuning through the VHF air band will generate a pop every time it changes the frequency. Even worse the AGC reacts to this pop as if it were a strong signal so the receiver becomes deaf if you tune too quickly. It's fine if you know what frequencies you want to monitor.
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  #611 (permalink)  
Old 06-17-2013, 11:25 AM
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airwolfbell222-

The primary mission of the CR-1 is to provide excellent HF reception. It does. As a bonus, it provides the VHF / UHF reception that it does. Not having been designed it to cover up to 380 MHz is the fact that this was not a primary requirement. It doesn't scan in the VHF / UHF bands either. Personally, I'd buy a dedicated scanner receiver that will provide better function scanning in these higher bands, and use the CR-1 for what it does best, which is HF reception. This is not something which can be fixed with a software revision, it is a true hardware limitation of the design. It IS a great radio!
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  #612 (permalink)  
Old 06-17-2013, 11:51 AM
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I would like to see a bit better AGC. On strong AM signals, like local talk shows it kind of drops out when there is a pause then comes back strong. It is hard to explain but the AGC just doesn't work real well in these situations. I am no electrical designer but the AGC just seems a bit off to me.

The other thing is a longer pause when you push the button to change modes and such, it reverts back too fast for me. Or else, just have the MODE button toggle through the modes with maybe the option to turn off modes you rarely use.

Has any thought been given to changing the horizontal line below the frequency into a bar-graph type S meter indication?

I still love the little radio, it brought the fun back to tuning around on HF.
Larry
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  #613 (permalink)  
Old 06-17-2013, 1:42 PM
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Quote:
Originally Posted by WB2KTG View Post
NRD-505

If you could call the shots, what would YOU fix and/or add to the CR-1?
The list of documented bugs.

How long is that list? May I see that list? May I choose from that list? Does someone presently calling the shots think that list is empty? Two examples of mine:

http://forums.radioreference.com/1968951-post451.html

It is noted that with the configuration HF/Shortwave/USA bandplan that the switchover from general to AM radio is 522kHz (like Europe rather than USA).

http://forums.radioreference.com/1969459-post454.html

HF/Shortwave/Automatic/USA when tuning down from 1720 to 1700 the tuning steps change from the "boxed" 5khz to the "solid" 10khz but when tuning from 1700 to 1720 the steps remain at 10khz and do not change back to the "boxed" 5kHz.

Are those bugs presently on that list?

The flow of information from CommRadio has come to a virtual standstill since Dayton. No newsletters.

At a major-three-letter computer company, the quickest and most painful way to generate what is called a "critsit" is to stop contact with the customer. From the vendor's point of view, I understand that the process of managing customers, processing orders and fixing bugs can be difficult and time-consuming and that sending out a message that says "we're fixing bugs" or "firmware is undergoing a major rewrite" might be considered a waste of time. I assure you that from the customer's point of view that message means a lot and goes a *long* way to improving overall customer satisfaction that can prevent an even more time-consuming critsit.

How's the beta firmware working out? Is there a beta undergoing testing? If not, then....????

My apologies if I sound a bit irritated, I am and it's irritation driven by anticipation.
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Old 06-17-2013, 4:14 PM
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I tell you what, I wasn't asked but I just want to bite .

This radio needs a bit of something that sets it apart. The CW decoder was a good start but not enough in my book. I look at this radio and as myself what it is offering me. Yes it is a good radio, yes I like enough to own it, yes for what it is I gave it a good review.

But really, what is thiis thing doing that my R75 can't? Sure, one could argue extra coverage but this was not a reason I bought it. I bought if for HF. Now, side by side what does it offer?

I like:
The small footprint
Sound (fine for my ears)
Battery

Now as I said the CW decoder is nice. But I can do this with the R75 with software, not to mention much more. And I can control the AGC and a host of other settings to dig out the signal with the R75. Ok, I understand this is a radio controlled by firmware (SDR), but it so much needs a modern SDR function to unlock what it could do. This radio can be so much more then what it is today with the help of a computer.

It would fly off the shelves in troves. Big money to be made. Data over USB and bingo, they hit a homerun.

I don't know whay it seems in this hobby you need 5 radios to get everything right? 1 time can we please have a radio that works and does things right? I mean break the barriers... Change the world... Bring new options but do so in a modern sort of way.
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Old 06-18-2013, 11:38 PM
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Default features I would like

I think they will address the pc integration in time. I am fine with that. The only thing I would hope for within the hardware radio usage side is to have the ability to select the agc.(fast med and slow) This radio is as sensitive as you really need(at least for me) and i find myself using this more than my other radios that have so many things to play with that I always find myself tweaking stuff rather than really listening, remember our ears are the best filters available if we really listen. The very fast agc acts very differently depending on your antenna use.
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Old 06-19-2013, 4:15 AM
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Built in CW decoders - in fact, any software based CW decoder- can be easily defeated because of the way the code is sent, noise, etc. It's not a deal breaker for me one way or the other, frankly, if I were to consider buying this radio.

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  #617 (permalink)  
Old 06-19-2013, 8:56 AM
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With a reasonably strong and clear signal the CR-1 CW decoder does work fairly well. Maybe not a deal breaker or maker but if you're already sold it does make the deal a bit sweeter. In my use it seems to outperform the MFJ-461.
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Old 06-19-2013, 11:26 AM
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When the going gets tough I find the R75 with FLDigi gets the job a lot more consistent (CW).
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Old 06-19-2013, 11:37 AM
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I have a free CW decoder on my Android phone that has been working better than the CR-1's decoder so it doesn't add any value to me. It needs some work to become a significant feature. As it is right now, it requires a nearly perfect signal to work reliably.
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Old 06-20-2013, 8:48 AM
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What happened to the announced price increase to $599 starting June 5th or was that just a gimmick to panic fence-sitters into buying? Commradio is still selling them for $500. Universal Radio price is screwy: "List price $650, Your Price $599. Intro Price $499.00."

"This is a one time DEAL $480 Dollar Special
The CR-1 will then go back up to $500 until June 4th. Starting June 5th it will go up to $599.
"

CommRadio offering sale on CR-1 for a limited time | The SWLing Post
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