test sugestion - analyzer and no int sweep generator

Thanks a lot ivan. you have made things a lot easier for me. this sort of test is something i havent done much of over the years.
my analyzer will hack -90dB and it looks as though i get -40db from an overloaded 16v zener as you sugested. from 15mhz to 40mhz the response is not flat - it drops abt 10db at 40mhz. but thats not a problem for looking at antennas and stuff.

Yes my chinese analyzer does have a peak hold but i never used it before. never thought about it. one of those functions i never used but now i see how it can benefit. just used it to re check a couple of 10m coax traps i made last year. i used the gdo to set them but the zener and analyzer also seem to do a good job as i can measure the bw too.

I suppose it would be a bit silly to use the noise generator and amplifier with harrys rf bridge to measure antennas? A 1/2 wave for 7 will also resonate on every odd harmonic all the way up to vhf. i know increasing the background noise was used for jamming in wwii. better stick to the generator.

I will try the noise trick with am hf rx but probably will not work with the nbfm? But that idea sounds great. you can adjust if bw just by watching the rx output.

Thanks for all your advice. Happy new year
/D

Hi all,
the modules from China may ease making the device. See e. g.
RF noise generator in a box
tracking noise generator including a chain of amplifiers 
small noise generator (maybe for AF only?)
broadband amplifier

If you have a spectrum analyzer with the "Max hold" function, you can tune a sinewave generator across the band of interest manually - only once.

VBR from Ivan

Hi Ivan,
I read your reply with interest. No doubt about it, there is a lot of knowledge to share on this forum.

I used noise generators for a while in a laboratory, but I also found that you can use conventional test equipment a little differently and get the same result. At the moment I have a lovely Vector Signal Generator that covers from 9 kHz to 3 GHz. RF output is up to 1 Watt  It is is perfect for testing antennas with 1 mW, a directional-coupler and an analyser.

I also use the FM side of it, using a sinusoidal and wind the deviation up to +/-300 kHz, then I can see antennas and wide-band TX filters on my analyser using the "Peak-Hold" function. If the signal generator is deviating by 600 kHz then it is linear-enough in the center to measure the 200 kHz wide 40 metre band antenna, for example.

@ Densil
1 - You wrote that you have a signal generator. Is it true signal generator with frequency modulation, or is it a function generator? If so then what is the maximum FM deviation you can get from it?
2 - Does your spectrum analyser have a Peak-Hold function? If so then you may not have to do many measurements: just slowly sweep the band with your signal generator holding the peak values.
3 - What sort of frequencies are you trying to test? I assume you are talking about 3 - 30 MHz plus maybe 455 kHz, 10.7 MHz and 21.4 MHz? ("Traps" are normally used for HF and low VHF, if you mean traps for antennas).

One of my colleagues at work is very avid constructor and he has recently built a nice box, using modules from China, to make a noise generator. Within any 2:1 frequency span the signal level is surprisingly flat and it pumps out a fair few milliwatts. If you are interested I will ask him for the component links for you? You have the test method from Ivan 

Very best regards from Harry - SM0VPO

Hi Densil,
a Zener diode working nearby its break voltage is a very good source of wideband white noise from AF to several GHz. A chain of MMIC RF amplifiers will bring the noise to the necessary level.
Filtering will be accomplished by the DUT (device under test)! If you use an extra filter, its amplitude characteristic may interfere with that of DUT and make the measurement less accurate. The method works even on mixers. You can e.g. couple the noise generator to an antenna input of a receiver and measure the AF spectrum on the speaker output. You will see the overall bandwidth of the entire receiver.

Merry Xmas!
VBR from Ivan

Hi Ivan. thank you for the reply. i guess i can overload a diode a bit and amplify the noise. i dont need a lot of noise as the analyzer will go down to 10uv.
i would think the rf powr would be really high if the noise frequencies was wide. maybe i need to filter the noise a bit to get only the band i am interested in? otherwise the total power in the spectrum could be really high?
thanks for the reply Ivan. you have a merry christmas
/D

Hi Densil,
the common way is to use a generator of white noise instead of a sinewave one. The spectrum analyzer displays the amplitude characteristic of a filter or amplifier in one step.

VBR from Ivan

Hi all. i have a low budget rf analyzer and a sig gen. the analyzer doesnt have a built in sweep gen.
Q) how can i use it to display a frequency respons like a filter or a wave trap?
at the moment i have to make dozens of measurements and plot them, but there could be a easy way?
thanks in advance
/D