A CLOSE LOOK TO LOW COST NOISE GENERATORS

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sdrom33
Posts: 34
Joined: Sun Dec 09, 2018 4:38 pm

Re: A CLOSE LOOK TO LOW COST NOISE GENERATORS

Postby sdrom33 » Sun Feb 17, 2019 5:57 am

Sorry again Roger, but you first made a big fuss about nothing. In your first post about the noise generator you only posted the guy telling the thing is junk and not to buy. If nobody commented about this and listened to you nobody buys the noise gen and nobody does any test. Then later you write many more things and pages, gives many references where they also tell how to fry eggs on the gen, but you yourself talk pages about it and now I see you have never even tested one yourself. With all this waste of time I do not know if I can use it or not. Please glovisol, can you give me some more clear idea about how it works? I have seen it is easy to make the filter, i have dowloaded the spec progzam and now need the gen.

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glovisol
Posts: 387
Joined: Thu May 10, 2018 6:42 pm
Location: Piedmont, Italy

Re: A CLOSE LOOK TO LOW COST NOISE GENERATORS

Postby glovisol » Sun Feb 17, 2019 8:59 am

Hi Sdrom33,

I am sorry and understand your frustration about this matter. At the end of the day, you, with a few words, went to the core of the matter, while we, the Wiseguys, the "We Know All Engineers" were not able to deliver what the less experienced guy really needs: certainty about the way to go. I apologise for this in all humility, for the most important scope of a Community Forum is to provide real help and clear cut information to other guys who need it and who share our interest in Radio Communications. What I should have done from the first would have been to write what comes next.

1) I have started using the Noise Generator in question in June 2018 and published work using it here:
viewtopic.php?f=5&t=3352

2) I purchased it as I was curious to learn by my own means how a such a low cost, wideband Noise generator would behave.

3) I was in fact gladly surprised by the performance I saw, considering the price, but MOST OF ALL I WAS HAPPY BECAUSE THE GENERATOR HAD VERY HIGH RF OUTPUT WHICH IS IDEAL FOR PASSIVE FILTER TESTING. In fact the higher the output, the higher the DYNAMYC RANGE you can measure on the Spectrum Analyser.

2) The BG7TBL was quoted by the vendor for a supply voltage of 12 V, but this was wrong information and the last amplifier stage failed after 15 days of operation. I bought another one, mounted it on a slab of wood together with a 9 V AC-DC power supply and this generator has been working happily in my lab since the end of June 2018. I also repaired the failed generator by bypassing the failed amplifier and use this when I need less RF output. SO, ACCORDING TO MY EXPERIENCE, THIS IS A RELIABLE PIECE OF EQUIPMENT, capable of working continuously for months. Additionally, it does not need any "modification": it works well enough as is.

3) In summary, according to my FIRST HAND experience, the generator is reliable and outputs the power you need to test the filter you wish to build. Furthermore I have published RF levelling performance in this thread, so you have all the info you need to take your decision and buy it. THIS IS THE SAME QUESTION OF ILLLIM WHO JUST NEEDED INFORMATION ON WHAT I HAD USED TO TEST THE FILTERS DESCRIBED IN THE THREAD and who also must have been confused and dismayed, learning from a single reference that the generator that had been used to develop the filters was "Chinese junk".

4) On the contrary the $100 generators advised by Roger do not fill the bill because, although they are more accurate in the stated frequency range, their power output, by reading their specs, is far lower. Then you have to start looking for a wideband amplifier etc., so you initiate a process that perhaps will take more effort than building the filter itself, while the $15 unit, fit for the purpose, is available already. This is what happens when you give advice based on the experience of others, while you only have some background theoretical experience. In fact it came as a surprise to me to read in his last post that Roger had not tested the unit himself.

To conclude, I agree the references provided by Roger are confusing: going through them you find horror (ridicolous?) stories, like that quickly noted by you about excessive heat and cooking eggs on the generator's board. And this brings me to another important point: you cannot publish references to the work and/or opinions of others without accepting any responsibility. You cannot, as Roger did, publish ONE reference stating that the generator is junk and stating you should not buy it, period and then deny any responsibility, refusing to come to a certain conclusion, as I read in his last post. This is not helping the other guy at all. I think it is much better service to the Community to write about YOUR OWN experience: any guy, in need for more information, can go and look on Internet on his own and form his own opinion, without the help of us, the Know All Engineers.

Sdrom33, do carry on with your work, I am very pleased that my effort with the filters is found to be useful by other Forum Members.

glovisol

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Roger
Posts: 217
Joined: Fri Dec 29, 2017 7:59 pm

Re: A CLOSE LOOK TO LOW COST NOISE GENERATORS

Postby Roger » Sun Feb 17, 2019 5:48 pm

sdrom33 wrote:Sorry again Roger, but you first made a big fuss about nothing. In your first post about the noise generator you only posted the guy telling the thing is junk and not to buy. If nobody commented about this and listened to you nobody buys the noise gen and nobody does any test. Then later you write many more things and pages, gives many references where they also tell how to fry eggs on the gen, but you yourself talk pages about it and now I see you have never even tested one yourself. With all this waste of time I do not know if I can use it or not.


This forum is a place for people to exchange ideas and to provide information for others. If you don't want to read other opinions about a product before making a purchasing decision that is up to you. Before I buy something I always read reviews by others and then make a decision based on whether the product meets my technical needs and is within my budget.

If a person decides not to buy a BG7TBL noise source that does not mean they cannot do any tests as you stated in your post. An Internet search with Google will give you several other buying options. I posted one link to several other products under $100 USD.

You questioned why I chose to post the Owen Duffy review. I did this for several reasons:

- The author gives a good defintion of Excess Noise Ratio (ENR) which is necessary prerequisite to understanding noise sources
- He gives an overview of the circuit design
- There is a spectrum analyzer plot of the noise level vs. frequency on the HF bands which was applicable to the discussion at hand
- He publishes technical specs for the device which the manufacturer did not provide
- He describes the device technical shortcomings including high voltage to the MMIC's which causes them to fail

Yes he does brand the product as "Chinese junk" but that is his opinion based on his technical analysis. Readers of the review can decide if they think that is reasonable or not based on his technical discussion. If curious they can do a Google search and learn more about this product.

I do not need to buy something myself and test it before making some comments that include links to product reviews. When other technically competent people have tested the device and documented the deficiencies I can learn from their observations. If multiple people come to the same conclusion about the quality and reliability of a product I see no need to buy one and waste my time and money coming to the same conclusion.

Reliability is a big issue with this product. In the links that I posted many individuals have stated that the MMIC amplifiers get very hot when run at the rated operating voltage. Several have found that the MMIC amplifiers fail due to heat and the noise source no longer works. Even the author of several articles in this forum who owns a BG7TBL had his own unit fail and had to repair it. He stated he needs to run it at lower than the design voltage in order to prevent another failure. This by definition makes it an unreliable product and in my opinion not worth buying.

Roger

.

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ON5HB
Posts: 88
Joined: Sat Dec 29, 2018 1:07 pm
Location: Heppen - Belgium
Contact:

Re: A CLOSE LOOK TO LOW COST NOISE GENERATORS

Postby ON5HB » Sun Feb 17, 2019 6:11 pm

All wrong, unless tested with Rohde & Schwarz there is no point discussing :lol:

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Greetings,

Bas - ON5HB

sdrom33
Posts: 34
Joined: Sun Dec 09, 2018 4:38 pm

Re: A CLOSE LOOK TO LOW COST NOISE GENERATORS

Postby sdrom33 » Sun Feb 17, 2019 7:10 pm

Sorry again Roger, you are happy to write a lot of extra which not helps anybody but please must admit that in your first post you mislead me and all and after you write a lot to cover up making a big book of it. Best regards

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Tech_Support
Posts: 437
Joined: Mon Jun 01, 2015 7:00 pm

Re: A CLOSE LOOK TO LOW COST NOISE GENERATORS

Postby Tech_Support » Sun Feb 17, 2019 7:39 pm

To all concerned,
I sincerely hope that this thread does not descend into personal antagonism. If it does, I am afraid I will be forced to delete the entire thread.

Please try to remain respectful and avoid all personal attacks, criticisms or insults. We are all here to help each other and everyone has a right to an opinion on any technical subject and equally everyone has a right to respectfully disagree.

Many thanks

Tech_Support

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Roger
Posts: 217
Joined: Fri Dec 29, 2017 7:59 pm

Re: A CLOSE LOOK TO LOW COST NOISE GENERATORS

Postby Roger » Sun Feb 17, 2019 7:50 pm

sdrom33 wrote:Sorry again Roger, you are happy to write a lot of extra which not helps anybody but please must admit that in your first post you mislead me and all and after you write a lot to cover up making a big book of it. Best regards


In my first post on this device I gave a link to a review of the BG7TBL noise source that I think is very informative and helpful to others. It was not useful to you or the other poster but you can't speak for everybody on this forum..

This product is not reliable for reasons I posted earlier and has poor noise spectrum characteristics. The only notable thing about it is the low price. However, as I have stated several times before it is useful for certain applications if you understand the limitations and know what you are doing. I won't buy one but you maybe it is acceptable to you.

I did not mislead you but if that is what you believe there is nothing I can say to change it. Why are you defending this product?
Please tell me why you think this device is worth buying.

Reason: No reason

Roger
Posts: 217
Joined: Fri Dec 29, 2017 7:59 pm

Re: A CLOSE LOOK TO LOW COST NOISE GENERATORS

Postby Roger » Sun Feb 17, 2019 8:02 pm

Tech_Support wrote:To all concerned,
I sincerely hope that this thread does not descend into personal antagonism. If it does, I am afraid I will be forced to delete the entire thread.

Please try to remain respectful and avoid all personal attacks, criticisms or insults. We are all here to help each other and everyone has a right to an opinion on any technical subject and equally everyone has a right to respectfully disagree.

Many thanks

Tech_Support


Tech_Support,

Throughout this discussion I have tried to focus solely on the technical issues and believe that I have been courteous to the other participants in this thread.

When a technical discussion turns unpleasant it makes me, and I suspect other forum members, question whether it is worthwhile to make comments or start topics on this forum. Thank you for stepping in and moderating this thread.

Roger

Reason: No reason

glovisol
Posts: 387
Joined: Thu May 10, 2018 6:42 pm
Location: Piedmont, Italy

Re: A CLOSE LOOK TO LOW COST NOISE GENERATORS

Postby glovisol » Mon Feb 18, 2019 8:51 am

Dear Tech_Support,

Please excuse me if it appeared that the defence not only of my work, but also of the tools used, was done in a perhaps too enthousiastic form.

This said, I consider the matter closed, as I have set forth, in (I hope) a balanced and realistic fashion, the reasons why the Noise Generator in question, despite hasty and perhaps little informed judgments, is a reliable piece of equipment, very useful in passive filter testing and available at a (miracolously) low price to us all. And this not by hearsay, but because I have personally tested and used it and will use it for a long time to come.

I would not tend to agree with the current prejudice that, if a piece of equipment is sold at a very advantageous price to the buyer, then it must be looked at with contempt. Such prejudice, I am afraid, if generally applied, can not only damage miriads of worthy products, but also remove many interesting opportunities from the scope of perspective buyers and users.

Finally let me remind to myself and us all that information publicly available, because published in the press, or loaded on Internet, is NOT the absolute thruth, just because it is published: behind this information there are always fallible human beings, like us all, so the principle that one must always try to think with his own brain is a good one.

I can only say I shall try to force myself to even more restraint in the future and thank you for pointing to us the way to reasonableness and mutual support.

With sincere appreciation,

glovisol

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sdrom33
Posts: 34
Joined: Sun Dec 09, 2018 4:38 pm

Re: A CLOSE LOOK TO LOW COST NOISE GENERATORS

Postby sdrom33 » Mon Feb 18, 2019 10:08 am

Hi tech support, excuse my English pse and also my posts, but I thought Roger wants to fool me and I was upset. I order the noise gen and am happy about all. Best regards,

Sdrom33

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