Testing RSPduo receiver sensitivity with noise generator

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vk7jj
Posts: 126
Joined: Thu Mar 02, 2017 9:56 am

Re: Testing RSPduo receiver sensitivity with noise generator

Postby vk7jj » Sun Jul 08, 2018 2:31 am

Yesterday I received a brand new Rig Expert's AA-30.ZERO Vector Impedance Anayser.


Hello Gianfranco, what a thrill! That will keep your imagination and fingers occupied for quite some time to come!

As mentioned in my message we lost internet for nearly two and a half days, we depend on a fixed-wireless tower, our sector is back online now but it was a pain. Monday evening (tomorrow) we have a granddaughter from far away staying with us for her school holidays. At 13 years she's involved with all our activities and more which is great but it means little or no radio-computer time just when things are getting interesting here and with your endeavours!

Oh well. I'm sure you and lots of others will more than make up for an absence from me.

Best regards till later, Phil VK7JJ

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glovisol
Posts: 172
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Location: Piedmont, Italy

Re: Testing RSPduo receiver sensitivity with noise generator

Postby glovisol » Sun Jul 08, 2018 9:44 am

Dear Phil,

Do not worry, take holiday from "Radio" and enjoy your child, they are such a fantastic company!

Today I took readings of the Beverage iust at the starting point, no lead-ins and did the scans both in the unterminated and the terminated condition. Comparing with yesterdays' results today's graphs are a real eye opener. I also downloaded the CS files and will work on the data in Excel not only to get useful quantitative results, but also to compare actual data with your model data. No leads and proper termination really put order and cleanliness in the picture! There is a lot to do.

Have a great sunday!

Gianfranco
Attachments
Short conn. unterminated 08.07.18.jpg
Eart Con. = 0.8 m / antenna drop to Anayzer: 5.5m- No termination at far side.
Short conn. unterminated 08.07.18.jpg (112.98 KiB) Viewed 1765 times
Short conn. terminated 08.08.18.jpg
Eart Con. = 0.8 m / antenna drop to Anayzer: 5.5m- 560 Ohm termination at far side.
Short conn. terminated 08.08.18.jpg (103.46 KiB) Viewed 1765 times

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glovisol
Posts: 172
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Location: Piedmont, Italy

Re: Testing RSPduo receiver sensitivity with noise generator

Postby glovisol » Tue Jul 10, 2018 7:42 am

Who followed this thread monitored VK7JJ's and my activity in researching, modelling and measuring a classic Beverage long wire antenna. I am now posting the results.

BEVERAGE ANTENNA MODEL CHARACTERISTICS & SPECIFICATIONS
Antenna length: 135 m.
Antenna supports: Receiving end, house wall with triple purchase tensioner & ceramic insulator.
Termination end: Telephone type wooden pole.
Antenna drop, receive side: 5m. Termination side: 5.5 m.
Antenna termination: 560 Ohm (10 resistors 5.6 KOhm in parallel). Termination is shown in Figure 1.
Antenna wire: plastic coated, 10 strand, brass plated steel wire. Each strand 0.3 mm dia. Total conductor diameter: 3 mm.
Total wire diameter with insulation: 4,5 mm. Wire resistance: 210 mOhm/m. Total antenna resistance:(135+5+5.5)*0,210 = 30.55 Ohm.
Average antenna height over ground between supports: 6 m.
Antenna transformer to Hi Z RDSduo input: Amidon F43 material ferrite toroid, outside diameter 9 mm. Enemelled wire 0.3 mm. dia. Primary (antenna): 5 turns; Secondary (RSPduo): 9 turns.

In next post comparison between modelled & measured data.
Attachments
Termination.JPG
Figure 1 - Far end 560 Ohm termination
Termination.JPG (213.98 KiB) Viewed 1723 times
Table 2.jpg
Table 2 - Modelled & measured data
Table 2.jpg (123.31 KiB) Viewed 1723 times
Compare 2-12.jpg
Figure 2 - Measured plot - Earth conn. 0,7 m to analiser - Ant. conn. drop 5m to analyser.
Compare 2-12.jpg (88.25 KiB) Viewed 1723 times

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glovisol
Posts: 172
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Location: Piedmont, Italy

Re: Testing RSPduo receiver sensitivity with noise generator

Postby glovisol » Tue Jul 10, 2018 1:17 pm

COMPARISON BETWEEN CALCULATED AND MEASURED DATA

In order to be able to compare modelled and measured data, I had to reduce the resolution of the Vector Analyser to just 12 points, so frequencies 2 to 14 MHz could be paired in both sets of data. With this resolution all measured parameter oscillations in between each MHz gap become invisible (look at Figure 2, previous post). Looking at Table 2, previous post, one can see that parameters, |Z| and Cp had to be computed from Rs and Xs originally available in both sets.

Looking at Figure 3, there is a fair correlation in antenna impedance |Z| and also in reactive part Xs. The surprising result is that actual impedance between 2.5 and 9.5 MHz is lower than modelled, while it was expected to be higher, due to the fact that the average antenna height, at 6 m. is significantly more than commonly used (see previous posts). Because of this result, I shall attempt to lower the termination resistance to 470 Ohm. In any case the Beverage antenna offers a very nearly resistive impedance over a very wide band: in fact Rs, Rp and |Z| coincide over all the frequency range considered.

There is also a fair correlation in SWR, as shown in Figure 4, not bad considering we are covering a frequency range of almost 3 octaves. However SWR was and is expected to improve with increasing frequency, as the ratio wavelength to antenna length becomes more favorable. This unexpected phenomenon will have to be investigated.

In Figure 5 we look at the equivalent parallel capacitance seen from the receiver. As expected parallel equivalent capacitance is significantly low at an average value of 15 pF, thereby "eating" very little received signal. This also explains the quite noticeable difference when the antenna terminal is pulled indoors thru the window: parallel capacitance goes up and the received signal goes down.
Attachments
SWR comparison.jpg
Figure 4 - Calculated & measured SWR
SWR comparison.jpg (65.79 KiB) Viewed 1655 times
Z comparison.jpg
Figure 3 - Calculated & measured Antenna impedance
Z comparison.jpg (88.03 KiB) Viewed 1710 times
Cp comparison.jpg
Figure 5 - Calculated & measured equivalent parallel capacitance Cp
Cp comparison.jpg (54.85 KiB) Viewed 1710 times

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glovisol
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Location: Piedmont, Italy

Re: Testing RSPduo receiver sensitivity with noise generator

Postby glovisol » Tue Jul 10, 2018 4:11 pm

For completeness here is Figure 6 showing antenna return loss 2 to 14 MHz, thick line. Thin line is return loss with the Material 43 toroid transformer in between. The antenna exhibits series capacitive reactance across most of the frequency range and it is easily tuned with a series coil: this would only be useful if one wished to use the antenna for transmission.

Using the triple purchase tensioner it is possible to change the average height of the antenna wire. Changing height from 6 to 3 m, impedance unexpectedly increased from 370 to 420 Ohm. More research is in order.
Attachments
2-14MHz  Return loss.jpg
Figure 6 - Return loss 2 to 14 MHz
2-14MHz Return loss.jpg (84.89 KiB) Viewed 1691 times

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Martin
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Re: Testing RSPduo receiver sensitivity with noise generator

Postby Martin » Wed Jul 25, 2018 7:44 pm

I was scanning the forums for something else; but came across this post so I thought I would add my two penn'orth.
After buying one of the Chinese noise sources from EBay, I was quite disappointed with the measurements I obtained with it, I couldn’t get repeatable results, and as I couldn’t be certain of its flatness nor it’s ENR, I was never sure if my problem lay in the RSP or the noise source! I was also aware of the huge amount of noise that was coming from the source and left wondering if the combined noise power of it all may damage the RSP front end. I also noticed that the MMIC’s run incredibly hot from 12V. Within a few months all of the above became irrelevant when the output MMIC died the same as the original poster here ‘glovisol’.
I then purchased a noise source here in the UK from this company http://g8fek.com/index.html. They not only sell calibrated noise sources but also general purpose ones which are suitable for amateur use. I originally brought a noise source to do simple tests of receiver noise figures by using the application note supplied on their website here (g8fek.com/uploads/9/4/4/3/94435411/rfdesign_an_-1_intro_to_noise_sources.pdf). I used their BBGen which has a flat +-1.5db output from 100KHz to 5GHz (datasheet here http://g8fek.com/uploads/9/4/4/3/944354 ... 090211.pdf) which produced some repeatable results using an RMS voltmeter, but I've since moved on to using the RSP (I use an RSP1 now discontinued) with the AGC off to produce the two noise on noise off results for the y factor measurement. There is a good tool and information on this method of noise figure measurement on the pages of Owen Duffy here (https://www.owenduffy.net/software/nfm/index.htm), I use the NFM application with manual entry to do the calculations.
To sweep filters I have followed the BBGen with a wideband MMIC based homebrew amp to sweep cavities at 177MHz and also filters at 28MHz using the RSP as the detector with manual gain adjustment. The same company sells a range of wideband amplifiers BBAxx (http://g8fek.com/lna.html) which have predicted gain and flatness, I have brought their BBA1 as the amplifier following my noise source to get a higher output level to enable me to add a return loss bridge between the output of the source and the antenna port of the RSP, that way you can look at the RL of ‘devices’ that you put on the unknown port of the bridge.
I have just noticed that they now sell an "RXGen" which has a +/-0.5db accuracy from 2MHz to 2,4GHz. Somewhat better than my original BBGen!
I have been to a few rallies and talked with the designer of these products, we even tested the RSP against a calibrated noise source at the Newark Hamfest last year, and all the numbers stacked up.

I eventually brought an RFD2305 calibrated source so that I could make meaningful measurements. For this post, I did a quick and dirty measurement using the RSP1 and the NFM app to show the gain and NF of a simple MAR8 MMIC amp in a milled box (Images at end of Post)

As you can see, the results are pretty good, the image below was taken from The MAR8 datasheet:-(Images at end of Post)

You just have to bear in mind that we are not talking about several thousand pound systems here; we are talking about low cost tools that will comfortably give you some meaningful and reproducible results within the ‘Amateur’ budget. As long as you keep the RSP device in its linear range, and make sure that you don’t overload the front end by adding too much amplification, the results that I have obtained have always stacked up with professional test kit within a db or so.


I do not work for RF Design UK, the only affiliation that I have with them is that I now know the designer well after discussing many of his products over the last few years. Over those few years have brought noise sources and broadband amplifiers from them. Not only have I been impressed by the quality of product, but the support I have received is excellent too.

Enjoy experimenting..
Martin
Attachments
1Setup.jpg
1Setup.jpg (108.29 KiB) Viewed 1557 times
2NFMResults.jpg
2NFMResults.jpg (95.28 KiB) Viewed 1557 times
3Mar8Spec.jpg
3Mar8Spec.jpg (14.96 KiB) Viewed 1557 times
Last edited by Martin on Thu Jan 01, 1970 12:00 am, edited 0 times in total.
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glovisol
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Location: Piedmont, Italy

Re: Testing RSPduo receiver sensitivity with noise generator

Postby glovisol » Thu Jul 26, 2018 7:21 am

Hi Martin,

Please accept my compliments and thanks for your most interesting and informative post. You opened up a vista on available noise and measurement devices completely unknown to me and probably to many others using this Forum.

Thanks again,

glovisol

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glovisol
Posts: 172
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Location: Piedmont, Italy

Re: Testing RSPduo receiver sensitivity with noise generator

Postby glovisol » Sat Aug 04, 2018 7:04 pm

Hi Martin, I have carefully gone over the literature you suggested and these products are of very good professional quality for receiver sensitivity measurements and for this use they have output levels in the order of -90 dBm.

My question is as follows: do you know of any supplier who markets a much higher power noise source (-40 dBm in a 10 KHz bandwith, like the one that burned out, but with serious reliability and good output precision over the specified bandwith? Such a source would be ideal to sweep passive RF circuitry.

Thanks,

glovisol

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glovisol
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Re: Testing RSPduo receiver sensitivity with noise generator

Postby glovisol » Wed Sep 12, 2018 11:32 am

I enclose simple schematic of attenuators for noise test. Keep noise generator supply voltage at +10V or less to avoid damage to noise generator board.

ERRATA CORRIGE: SCHEMATIC REMOVED BECAUSE OF WRONG VALUES. RIGHT & BETTER SCHEMATIC IN NEXT POST!!

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g1hbe
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Location: Cheshire, UK

Re: Testing RSPduo receiver sensitivity with noise generator

Postby g1hbe » Wed Sep 12, 2018 11:50 am

Glovisol, has something gone amiss with your calcs? Those attenuators won't be anywhere near 46 dB. You'd need about 5k in series.

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Andy


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