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Poor mans spectrum analyzer #ubitx

Nigel G4ZAL
 

I have no sophisticated bench test gear so I used my hackRF and the free Spectrum Analyzer software to 'look' at what my uBitx was transmitting whilst on FT8 on 7.074MHz and the result is quite disappointing although not unexpected.
uBitx was on an EFHW for 40M and the hackRF was on a short whip antenna.

I have some Axicom relays and shielded SMD inductors for L5/7 and will compare results after swapping out the bits and see if I can 'clean up my act' !

Nigel

spec_an1.jpg

 

I don't know the circuit of the hackRF, but I wouldn't use any antenna connected to the SDR. You could fry its frontend unless it has some protection (I.e. Back to back diodes) at the antenna input. You just see a lot of overloading of your receiver. Having a 8bits ADC the dynamic range is similar to the RTL stick, 48db, so you need to attenuate a lot at least removing the antenna.


Il 03/nov/2018 18:53, "Nigel G4ZAL" <nigel@...> ha scritto:
I have no sophisticated bench test gear so I used my hackRF and the free Spectrum Analyzer software to 'look' at what my uBitx was transmitting whilst on FT8 on 7.074MHz and the result is quite disappointing although not unexpected.
uBitx was on an EFHW for 40M and the hackRF was on a short whip antenna.

I have some Axicom relays and shielded SMD inductors for L5/7 and will compare results after swapping out the bits and see if I can 'clean up my act' !

Nigel
 

Hey Nigel, what free Spec. Analyzer do you?have?

73 Ken
VA3ABN

On Sat, Nov 3, 2018 at 5:45 PM iz oos <and2oosiz2@...> wrote:

I don't know the circuit of the hackRF, but I wouldn't use any antenna connected to the SDR. You could fry its frontend unless it has some protection (I.e. Back to back diodes) at the antenna input. You just see a lot of overloading of your receiver. Having a 8bits ADC the dynamic range is similar to the RTL stick, 48db, so you need to attenuate a lot at least removing the antenna.


Il 03/nov/2018 18:53, "Nigel G4ZAL" <nigel@...> ha scritto:
I have no sophisticated bench test gear so I used my hackRF and the free Spectrum Analyzer software to 'look' at what my uBitx was transmitting whilst on FT8 on 7.074MHz and the result is quite disappointing although not unexpected.
uBitx was on an EFHW for 40M and the hackRF was on a short whip antenna.

I have some Axicom relays and shielded SMD inductors for L5/7 and will compare results after swapping out the bits and see if I can 'clean up my act' !

Nigel
Nigel G4ZAL
 

Agreed on the front end of the hackRF - this one has already been repaired by me as a friend gave it to me and said, it's deaf - if you can get it going again, it's yours as I have got a new one!
They are renowned for frying the pre-amp chip if it is activated and then a strong nearby signal is fired up close to it and that's what I had to replace (the pre-amp chip) to get it running again.
Apparently, Hams are often keying a handheld too close to it :-(


I used it with a short 1ft (30cm) whip and low gain settings in the spec-an software/hackRF, that's the best way to run it, low gains and increase as needed.
Without any antenna connected, I only saw the main signal at low levels.

The free spec-an s/ware for the hackRF is here, in Linux and Windows flavours (scroll down to the 'Downloads' section)...

I didn't need to run Zadig in my Windows 7 64bit machine as the hackRF installed in Windows automatically.

If you have a cheap RTL-SDR dongle and hack it for HF/use a converter, you can find spectrum analyser software for them as well.

Nigel.
 

Yep, this keeps coming up in different forms. I agree you need to attenuate your receiver because of overloading the receiver. You are showing a common overload image on a SDR receiver. With my SDR I have a strong signal from my BITX 40 without an antenna on the SDR at all. I haven't tried to see how well I can accurately test the signal that way, but I would think a dummy load on the TX, and no antenna on the RX might be the easiest way to get a better picture of your emissions being tested in the same room. And don't use what ever you are doing for more power either, go barefoot.
Joe Puma
 

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I¡¯ve used my 100 watt radio next to a receive antenna for a rtl-sdr. I have fried am/fm filters and the sv1afn upconverter (a few times) but never the dongle. I have locked them up on the usb bus and had to unplug them to reset but that¡¯s about it. You will overload the dongle with an antenna going outside but without anything plugged in it might make it deaf for a ubitx with outside antenna and you in the house. A indoor whip seems doable or a piece of wire.?

I could see you using it as a comparative measurement tool. I¡¯ve used a rtl-sdr to look at characteristics of a filter with a cheap eBay noise source or using a directional coupler to measure swr of antennas. I¡¯m still an infant out here but I¡¯ve played with sdr¡¯s for a while. Baby toys for beginners I guess lol?


Joe



On Nov 3, 2018, at 5:45 PM, iz oos <and2oosiz2@...> wrote:

I don't know the circuit of the hackRF, but I wouldn't use any antenna connected to the SDR. You could fry its frontend unless it has some protection (I.e. Back to back diodes) at the antenna input. You just see a lot of overloading of your receiver. Having a 8bits ADC the dynamic range is similar to the RTL stick, 48db, so you need to attenuate a lot at least removing the antenna.


Il 03/nov/2018 18:53, "Nigel G4ZAL" <nigel@...> ha scritto:
I have no sophisticated bench test gear so I used my hackRF and the free Spectrum Analyzer software to 'look' at what my uBitx was transmitting whilst on FT8 on 7.074MHz and the result is quite disappointing although not unexpected.
uBitx was on an EFHW for 40M and the hackRF was on a short whip antenna.

I have some Axicom relays and shielded SMD inductors for L5/7 and will compare results after swapping out the bits and see if I can 'clean up my act' !

Nigel
Joe Puma
 

¿ªÔÆÌåÓý

Here are some other softwares you can try.



If you have a sdrplay

Joe


On Nov 3, 2018, at 7:51 PM, Joe Puma <kd2nfc@...> wrote:

I¡¯ve used my 100 watt radio next to a receive antenna for a rtl-sdr. I have fried am/fm filters and the sv1afn upconverter (a few times) but never the dongle. I have locked them up on the usb bus and had to unplug them to reset but that¡¯s about it. You will overload the dongle with an antenna going outside but without anything plugged in it might make it deaf for a ubitx with outside antenna and you in the house. A indoor whip seems doable or a piece of wire.?

I could see you using it as a comparative measurement tool. I¡¯ve used a rtl-sdr to look at characteristics of a filter with a cheap eBay noise source or using a directional coupler to measure swr of antennas. I¡¯m still an infant out here but I¡¯ve played with sdr¡¯s for a while. Baby toys for beginners I guess lol?


Joe



On Nov 3, 2018, at 5:45 PM, iz oos <and2oosiz2@...> wrote:

I don't know the circuit of the hackRF, but I wouldn't use any antenna connected to the SDR. You could fry its frontend unless it has some protection (I.e. Back to back diodes) at the antenna input. You just see a lot of overloading of your receiver. Having a 8bits ADC the dynamic range is similar to the RTL stick, 48db, so you need to attenuate a lot at least removing the antenna.


Il 03/nov/2018 18:53, "Nigel G4ZAL" <nigel@...> ha scritto:
I have no sophisticated bench test gear so I used my hackRF and the free Spectrum Analyzer software to 'look' at what my uBitx was transmitting whilst on FT8 on 7.074MHz and the result is quite disappointing although not unexpected.
uBitx was on an EFHW for 40M and the hackRF was on a short whip antenna.

I have some Axicom relays and shielded SMD inductors for L5/7 and will compare results after swapping out the bits and see if I can 'clean up my act' !

Nigel

<spec_an1a.jpg>

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