3 dB HYBRID COUPLER/ISOLATOR FOR ANTENNA SPLITTING 100 KHz -10 MHz

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glovisol
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Re: 3 dB HYBRID COUPLER/ISOLATOR FOR ANTENNA SPLITTING 100 KHz -10 MHz

Postby glovisol » Tue Apr 16, 2019 7:41 am

THE HIGH IMPEDANCE ASYMMETRICAL 3 dB HYBRID COUPLER

The prevously discussed 3 dB hybrid, that works with equal 50 Ohm coaxial impedances on all ports, is useful for joining a 50 Ohm coaxial antenna lead to two 50 Ohm coaxial receiver inputs. Long wire or Beverage antennas with termination impedances in the order of 560 Ohm would require a 560 to 50 Ohm transformer. Additionally, the very useful balanced input provided by some RSP receivers (e.g. RSPduo or RSP2) would require another extra transformer 50 Ohm to 1 KOhm.

By judicious choice of hybrid impedances and by addition of transformers as integral parts of the coupler, it is possible to accommodate any input and any output impedance at the three ports, keeping total losses in the 1 to 2 dB range, which are negligible, at LF, MW and low HF bands.

The example below shows a 3 dB coupler with a 560 Ohm balanced input for accommodating a long wire antenna, one 50 Ohm coaxial output and one 1000 Ohm balanced output + common, ideal for the HI Z input of the so equipped RSP receivers. Such a coupler is useful for comparing two inputs of the same receiver, or for comparing two different receivers with different input impedances, while at the same time eliminating the danger of crossed receiver radiation altering the measurements. Note that amplitude variations with frequency, shown in the screens below, depend only on the Noise Generator output characteristics, as demonstrated by the top trace, obtained by connecting directly the attenuated Noise Generator output to the RSP-1A input.

Additional information in the next posts.
Attachments
HI Z Hybrid 1.jpg
HI Z Hybrid 1.jpg (321.81 KiB) Viewed 1827 times
HI Z Hybrid 2.jpg
HI Z Hybrid 2.jpg (352.94 KiB) Viewed 1827 times
HI Z Hybrid Pict..JPG
HI Z Hybrid Pict..JPG (178.94 KiB) Viewed 1827 times

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glovisol
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Re: 3 dB HYBRID COUPLER/ISOLATOR FOR ANTENNA SPLITTING 100 KHz -10 MHz

Postby glovisol » Tue Apr 16, 2019 11:44 am

LOCAL OSCILLATOR RADIATION FROM ANTENNA INPUT

There has been speculation in this thread about the RSP's not having Local Oscillators and Mixers and therefore being devoid of L.O. radiation. A good explanation of the frequency conversion arrangement of the RSP class of Spectrum Processors is given here:

https://www.sdrplay.com/docs/SDRplay_Op ... _MW_HF.pdf

Briefly all incoming signals in the range 0-60 MHz are converted to a first I.F. of 120 to 180 MHz by a fixed L.O. operating at a frequency of 120 MHz. This first I.F. is then converted, by mixing with a Synthesiser signal (2nd L.O.) down to ZERO I.F. or to a LOW I.F. Thus very low level 1°st & 2°nd Oscillator signals may be detectable at any RSP Antenna input connector.

Local Oscillator detection was implemented using an RSP-1A driven by Spectrum Analyser software and an RSPduo driven by SDRuno. The two receivers were interconnected by means of a coaxial 50 Ohm cable. L.O. oscillator levels detected are in the order of -120 to - 130 dBm, a level testifiyng to the good quality of this design. Test results are uploaded below.
Attachments
LO Radiation 2.jpg
Units not interconnected: Spectrum Analyser shows L.O. of RSP-1A & SDRuno L.O. of RSPduo
LO Radiation 2.jpg (308.25 KiB) Viewed 1799 times
LO Radiation 1.jpg
Units interconnected
LO Radiation 1.jpg (315.44 KiB) Viewed 1799 times
LO Radiation 3.jpg
Units interconnected & display zoomed
LO Radiation 3.jpg (329.39 KiB) Viewed 1799 times

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glovisol
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Re: 3 dB HYBRID COUPLER/ISOLATOR FOR ANTENNA SPLITTING 100 KHz -10 MHz

Postby glovisol » Wed Apr 17, 2019 7:09 am

THE HIGH IMPEDANCE ASYMMETRICAL 3 dB HYBRID COUPLER

Core material is the same as for the 50 Ohm hybrid.
For our wideband LF 3 dB Hybrid the 560 Ohm primary winding must have a reactance Xl=560*4 > 2000 Ohm @ 100 KHz, hence:

BALANCED HYBRID TRANSFORMER T1
L= (1000*10^6)/(2*PI*10^5) > 1600uH
N > 100 * SQRT(2000/118,000) = 13 turns, With reference to the schematic diagram, we shall use 11.5 turns for N1
Secondaries N2 and N3 must be identical and at 560 Ohm impedance level. Ratio is 1.43:
N2 = N3 = 12/1.43 = 8.39 turns. With reference to the diagram we shall use N2=N3= 8. 5 turns.
Balancing resistor R1+R2 = 560/2 = 280 Ohm made with 270 + 10 Ohm.

TRANSFORMER T2 560 TO 50 OHM
Primary @ 560 Ohm: N4=11.5 turns
Secondary N5 = 12*SQRT(50/560) = 12*0.299 = 3.5 we shall use N5=3.5 turns

TRANSFORMER T3 560 TO 1KOHM
Primary @ 560 Ohm: N6=11.5 turns
Secondary N7 = 12*SQRT(1000/560) = 12*1.33 = 16 we shall use N7=16.5 turns

Wire data is given in the schematic uploaded below. Tests in next post.
Attachments
Hi Z Hybrid Schematic & Data.jpg
Hi Z Hybrid Schematic & Data.jpg (115.48 KiB) Viewed 1761 times

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glovisol
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Re: 3 dB HYBRID COUPLER/ISOLATOR FOR ANTENNA SPLITTING 100 KHz -10 MHz

Postby glovisol » Thu Apr 18, 2019 1:35 pm

TESTING THE HIGH IMPEDANCE ASYMMETRICAL 3 dB HYBRID COUPLER

The asymmetrical hybrid performance data mentioned in the previous posts has been obtained with the test setups pictured in the screens posted below.

For the FORWARD TEST the Noise Generator output is connected to the input port, the 50 Ohm port is terminated with a 50 Ohm load and the HI Z 1 KOhm input port is connected to the RSP-1A/Spectrum Analyser via a 1 KOhm to 50 Ohm transformer.

For the ISOLATION TEST the input port is terminated into a 560 Ohm resistor, Noise Generator output feeds the HI Z port through a 50 Ohm to 1 KOhm transformer and the 50 OHm output port is connected to the RSP-1A to measure the attenuation between these two ports.
Attachments
Hybrid forward test.JPG
Hybrid forward test.JPG (281.38 KiB) Viewed 1716 times
Hybrid isolation test.JPG
Hybrid isolation test.JPG (223.48 KiB) Viewed 1716 times

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ON5HB
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Re: 3 dB HYBRID COUPLER/ISOLATOR FOR ANTENNA SPLITTING 100 KHz -10 MHz

Postby ON5HB » Thu Apr 18, 2019 4:31 pm

I tested a splitter for the RSP1A.

Normal situation is T-connectors to 3x RSP1A.

I tried an splitter 5-2500MHz, splitted and the signals went down a lot.

This makes me believe that the input of the RSP1A is not 50 Ohm but very high impedance.
My splitter made a big impact on the signals, where my default T-split did not.

As such I took the splitter from the websdsr, there is no benefit at all.

My websdr does HF but upconverted with 125MHz, splitting with a proper 50 Ohm splitter made signals worse then with just T connectors.

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Greetings,

Bas - ON5HB

sdrom33
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Re: 3 dB HYBRID COUPLER/ISOLATOR FOR ANTENNA SPLITTING 100 KHz -10 MHz

Postby sdrom33 » Thu Apr 18, 2019 6:04 pm

It could help to know what splitters you are using. The RSP1a input is rated 50 Ohm, why should it be different? Why should sdrplay give wrong info & specs?

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glovisol
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Re: 3 dB HYBRID COUPLER/ISOLATOR FOR ANTENNA SPLITTING 100 KHz -10 MHz

Postby glovisol » Fri Apr 19, 2019 6:57 am

ON5HB wrote:I tested a splitter for the RSP1A.

Normal situation is T-connectors to 3x RSP1A.

I tried an splitter 5-2500MHz, splitted and the signals went down a lot.

This makes me believe that the input of the RSP1A is not 50 Ohm but very high impedance.
My splitter made a big impact on the signals, where my default T-split did not.

As such I took the splitter from the websdsr, there is no benefit at all.

My websdr does HF but upconverted with 125MHz, splitting with a proper 50 Ohm splitter made signals worse then with just T connectors.


THE INPUT IMPEDANCE OF THE RSP-1A

1) With reference to the blocks diagram, we see that the input of the RSP-1A is switched among input filters, depending on the frequency range selected. So input impedance must be measured within a well specified frequency range and with the RSP-1A turned on and working in the same range. The WORST CASE measurement is done with no attenuation inserted (e.g. maximum gain, position 0) because the built in attenuator subtantially improves the VSWR by providing resistive load to the input port.

ERRATA CORRIGE 23/04/19: Here below I have stated that the output of the AA30-Analyser is 0 dBm maximum. This value is what I have measured in the 3-10 MHz frequency range. However the AA30 specification states that the output can be as high as + 10 dBm, SO GREAT CARE MUST BE USED IN THE DESCRIBED MEASUREMENT, which must be done in a matter of seconds! I apologise for this mistake.

2) The measurement can be done with a Network Analyser, provided the output RF of this device is always less than or equal to 0 dBm. The AA30-Analyser outputs a constant 0 dBm signal, so it is suitable and there is no danger of damaging the RSP under test, provided you make it last a few seconds.

Input impedance has been measured in the range 3 to 10 MHz, having the RSP-1A set at 5 MHz center frequency, with DEC=1 & SR=10 MHz. The excellent results posted below show that indeed the input impedance is an accurate 50 Ohm, with minimum return loss in the order of 8 dB across the frequency range measured.
Attachments
RSP1A_Input Z_1.jpg
RSP1A_Input Z_1.jpg (145.46 KiB) Viewed 1666 times
RSP-1A_Input Z_2.jpg
RSP-1A_Input Z_2.jpg (144.45 KiB) Viewed 1666 times
RSP-1A_Input Z_3.jpg
RSP-1A_Input Z_3.jpg (155.6 KiB) Viewed 1666 times

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ON5HB
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Re: 3 dB HYBRID COUPLER/ISOLATOR FOR ANTENNA SPLITTING 100 KHz -10 MHz

Postby ON5HB » Fri Apr 19, 2019 3:52 pm

sdrom33 wrote:It could help to know what splitters you are using. The RSP1a input is rated 50 Ohm, why should it be different? Why should sdrplay give wrong info & specs?


What do you mean wrong info and specs?
It's not a transmitter but a receiver, as such impedance isn't crucial to good workings.

Reason: No reason
Greetings,

Bas - ON5HB

sdrom33
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Re: 3 dB HYBRID COUPLER/ISOLATOR FOR ANTENNA SPLITTING 100 KHz -10 MHz

Postby sdrom33 » Fri Apr 19, 2019 5:54 pm

ON5HB wrote:
What do you mean wrong info and specs?
It's not a transmitter but a receiver, as such impedance isn't crucial to good workings.


Exactly what I wrote. The official published specifications by Sdrplay say: 50 Ohm input impedance. If you write in so many words it is not so, you are being unfair to Sdrplay and misleading other forum members. It is not a question of "transmitter" or "receiver".
If you are sure that the Rsp1a input impedance is not 50 Ohm, open a ticket. Anyway if you look at the previous post you can see the rsp1a input impedance is 50 Ohm spot on.

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glovisol
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Re: 3 dB HYBRID COUPLER/ISOLATOR FOR ANTENNA SPLITTING 100 KHz -10 MHz

Postby glovisol » Sun Apr 21, 2019 3:20 pm

NETWORK ANALYSER MEASUREMENTS

Shown below is what the antenna sees looking into the 50 Ohm splitter connected to two receivers in operation in the frequency range 3 to 10 MHz. It can be seen that the antenna looks at a high quality 50 Ohm termination, with a return loss always above 10 dB.
Attachments
Antenna looking into 50 Ohm splitter 1.jpg
Antenna looking into 50 Ohm splitter 1.jpg (97.41 KiB) Viewed 1496 times
Antenna looking into 50 Ohm splitter 2.jpg
Antenna looking into 50 Ohm splitter 2.jpg (109.46 KiB) Viewed 1496 times
Antenna looking into 50 Ohm splitter3.jpg
Antenna looking into 50 Ohm splitter3.jpg (78.2 KiB) Viewed 1496 times

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