FlightAware Discussions

New model of BG7TBL noise source


I noticed today that there is a new version of the popular BG7TBL noise source dated 2016-02-06. Prior to this the most recent version I had seen was 2014-08-20, and those often had a limited life span due to excessive heat. There are many of the usual Chinese vendors selling this new model, as well as many still selling the 2014 model.

The amplifier chips appear to be different, and the new one doesn’t have the electrolytic capacitors like the old one did.

I’m curious if anyone has tried this new model and found any improvements, and if anyone knows what the amplifiers are that replaced the three ERA-5+ chips used on the 2014 model?


Do you mean this one? Havn’t tried it but is still pulling around 160ma, maybe a bit less than the older BG7 ones but it is still going to get fairly hot.
I have one of the origional BG7 here that has had quite a bit of use over the last 6 months and is still going strong but they do need a fan mounted to the board.


I purchased the one in picture below last year.
It failed after one week.
It generated so much heat that during it’s one week life, I used it for frying eggs. :smiley:

Roll your own Interdigital filter

That appears to be a different, more costly one. Here’s a link to the one I saw:
I have the 2014 model and am in the process of replacing the amplifier chips, and adding heat sinks and a fan. Hoping to preserve it better this time.


After bitter experience of noise-source, I have decided to purchase a Signal Generator:

Low Cost Signal Generator (35Mhz-4.4Ghz) for antenna testing



Has anyone used any of these Signal Generators?


The one you linked to looks like it needs a 300ma power supply so it will probably generate the same heat as the old ones.
My 2104 model one has been fine with just the fan so with the heatsinks as well, your repaired one should go for years :slight_smile:


This remedy came too late for me. Unfortunately my Noise Source is already dead. If I only knew before it’s death, my Noise Source will be alive today…

Anyway I am now considering a low-cost Signal Generator, as it will enable me to measure the SWR of antennas, whereas noise source does not.


@abcd567, It was probably the demise of your noise source that alerted me to the issue in the first place, so thanks! (if thats any conciliation :slight_smile: )

The noise source and directional coupler does the SWR ok, for what I need anyway. Measuring an open feed line gives you infinate’ish SWR then a good 50ohm dummy load gives ~1:1, the rest can be converted from the db scale between these points. Its probably as good a number as any uncalibrated non professional gear is going to give.

I think I mentioned this previously and I know you are quite familiar with the effects of standing waves. But I’ll rant on anyway. The main thing I found in getting useful results that isn’t mentioned in all the YouTube videos etc, is keeping the feed-lines as short (preferably non existent) as possible. It’s hard enough coming to grips with the results when not having to get your head around the effects of the standing waves and differences that small changes in feed-line length can have on results.

To get the best out of a tracking signal gen or a noise source, I think its important to see the results warts and all on a spectrum display rather than just a number on a meter that often where where feed-lines are involved, means nothing.


Thanks for the photo. Once repaired, I may forego the heat sinks and just go with the fan. Hadn’t figured out how I was going to mount heat sinks on those tiny ‘blobs’ anyway. It’s be good to be able to get back to some testing.



WARNING : BG7TBL noise source 20160206 exist in two versions with exactly the same components, datum and layout. But one is BAD due to faulty VIA’s. It is instable and oscillates. Recognise the faulty one by nearly all -very small- vias which have NO open hole and no tinned border, and they make NO contact wikt mass planes.
So its bottom “mass plane” is not properly connected to upper mass plane, and instead acts as a coupling plane => oscillatons and very strong “hand effect” if near a side or bottom. The "good version has all less small vias with OPEN holes and tinned borders, which are not insulated from mass planes.
73’s, Nico.


Typical for Chinese quality control.


Lol i think the board i just got is one of the bad ones.
About 50 dud vias and maybe 8 that look fine.

I guess i’ll get out the drill and make myself some vias.
Does acetone dissolve solder mask? Or do i need another solvent for that?


I ordered this one like a week ago, is it the bad one?? https://www.ebay.com/itm/SMA-noise-source-Simple-spectrum-external-tracking-source-DC-12V-0-3A/111831285650



CAUTION: Do NOT use 12V DC adapter with BG7TBL noise generator. Although its specs say 12V DC, it gets extremely hot when used with 12V DC.

Use 5V DC Adaptor.

With my first noise generator, I have ordered 12V DC adaptor. After a week, the board fried itself.

When I purchased next one, I ordered a 5V DC adaptor, and the noise generator does not overheat, and works perfectly well.



Funny, I see there a switched mode power supply (the IC). That should feed the rest of the board.

The noise generator is a reversed polarized avalanche or zenner diode, amplified by three wide band amplifier modules (those indeed have max voltage something like 5.5V).


Someone figured out they sell more of the boards if they print 12V instead of 5V onto them. -.-


I can recommend where to place connections between bottom and top mass planes, as i got the bad PCB working now. Try to keep the hole in each via open for better RF connection.

Make vias :

Close to the border ofthe PCB:
Under : R18, C21, U3, U2, R15, D4,.
To the left of : C3 and D1.
Above R16.
Solder the output connector at the bottom side.

Directly in the cooling fin island of each MMICs.

Directly at the mass connections of C11, C16, C17, C8.

At the left of U1 (mass).

Better solder 100uF/16V capacitors in parallele to : C11, C16, C17. C8.
Solder 100uF / 63V in parallel to C1.
This helps preventing noise below 200kHz from an external SMPS supply and the 38V converter U1.

I also short circuited L6, L7, L8 with a wire. This makes the frequency characteristic less hilly in my experience.

Try changing R11 into 82 kOhms (yes eighty two kilo ohms). It gave me a flatter frequency characteristic.
Check the difference.


My PCB is now still more changed so it is all powered from 12V :
U1 is now disconnected from 12V, and R11 removed.
R15 is short circuited.
R17 is removed.
R19 is now 120 Ohms.
D4 is 4.7V 500mW. D4 gets 37mA via 100 Ohms from a 78L09. Its output is decoupled to maas by 1nF + 10nF + 100nF + 100 uF. The 1nF is important for high frequency characteristic, hold wires short.

Output -50dBm @ 3.7 MHz.
Flat from 25 kHz to 3.2 MHz +/- 1dB.
50 MHz -19dB.
Flat from 60 MHz to 160 MHz within +/- 1dB.

Power : 12V 280 mA. Tested wit 14.6Vdc 320mA, no break down.

NO hand effect anymore when near the border or undeside of the PCB.
NO oscillations anymore.
NO unstable (jumpng) noise output.

When in a box, then metal, and a lot of ventilation holes. One ground connection to the box at the output connector.

But i designed my own new PCB. Must save money for odering it and make a new test version.

I removed this topic from my dite as it is to much work for correcting a junk PCB.

Please report me your findings. Maybe also interesting for others.

73’s, Nico pa0nhc. www.pa0nhc.nl


Thanks for detailed writeup.
It is hard (for me at least) to understand by writeup alone.
Few photos will be of great help.


@ pa0nhc

  1. I don’t see the 78L09 on the board. Probably you meant that you have added one? If indeed the Zenner diode D4 is 4.7V, feeding the whole device with only 5V will make it work really poorly (if at all).
  2. Also the U1 converter - I think you meant 3.8V? That would be used to feed the three amplifiers. I cannot quite make up the markings on the IC’s in the pic.