THIS THREAD EXPLAINS WHY IT IS SO DIFFICULT TO UNDERSTAND RECEIVER'S SENSITIVITY IN LF & RELATED MATTERS

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glovisol
Posts: 269
Joined: Thu May 10, 2018 6:42 pm
Location: Piedmont, Italy

Re: THIS THREAD EXPLAINS WHY IT IS SO DIFFICULT TO UNDERSTAND RECEIVER'S SENSITIVITY IN LF & RELATED MATTERS

Postby glovisol » Sun Jan 13, 2019 12:48 pm

THE RSP-1A on LONG WAVE

- RECEIVER.......................................RSP-1A.
- ANTENNA.......................................135m Beverage.
- IF MODE.........................................Low IF.
- FEED.............................................550 to 50 Ohm Isolation transformer / primary inductance: 3.8 mH.
- ATTENUATOR..................................5 dB type "H", 550/550 Ohm between antenna & Isolation transformer.
- PC................................................IBM X61 laptop with battery supply.


BBC Radio 4 on 198 KHz @ 12:00 GMT / 13/01/19
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ON5HB
Posts: 19
Joined: Sat Dec 29, 2018 1:07 pm

Re: THIS THREAD EXPLAINS WHY IT IS SO DIFFICULT TO UNDERSTAND RECEIVER'S SENSITIVITY IN LF & RELATED MATTERS

Postby ON5HB » Sun Jan 13, 2019 3:00 pm

Hi there,

I had this problem too in the past, the main issue is the low frequency and major signals close together.
That is where mixing starts, the I/Q can't be separated well, it simply can't work out a good signal from a bad one.

Baluns and other stuff do not help, tried everything including ordering attenuators a big as -30 and combined got to 60dB, didn't matter.

The solution I use is simple, use an up-converter of 125 MHz like the NoElec (metal boxed with TCXO), it will greatly solve the problem as the local-oscillator and band-filters are very high so mixing doesn't happen that much and the I/Q is far better.

I learned this little trick from using dongles in he past.
I'm running a websdr, so you can see what it does here: http://heppen.be?tune=198am

The antenna is a 54m long-wire, fed with coax, no baluns, just a lot of ferrite clamped on the coax as common-mode-choke (but one can use a plastic bottle too and wind coax round it for about 20 turns).

After the up-converter I did set MW-notches and LNA-on, works great.

As far as the RSP1A is concerned, it thinks it's tuning in VHF rather then HF, but the trick works great.
See for yourself, but do not take the values for real, just set them to what seems to be right:

Schermafdruk op 2019-01-13 16-26-11.png
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Or as you look at it:
Schermafdruk op 2019-01-13 16-29-21.png
Schermafdruk op 2019-01-13 16-29-21.png (58.54 KiB) Viewed 116 times


I do point out, I'm using 5 MHz BW with decimate of 2, as I need the entire 2MHz sampled at the same attenuation, doing so band/low-pass don't work well (if hardly at all) without up-converting.

Just my thoughts on the matter, hopefully it works for you too.

73's Bas.

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glovisol
Posts: 269
Joined: Thu May 10, 2018 6:42 pm
Location: Piedmont, Italy

Re: THIS THREAD EXPLAINS WHY IT IS SO DIFFICULT TO UNDERSTAND RECEIVER'S SENSITIVITY IN LF & RELATED MATTERS

Postby glovisol » Sun Jan 13, 2019 4:38 pm

Hi Bas,

Thanks for the information and the suggestions, which I will try out.

I am also testing the RSP-1A with just a self made ferrite balun (described in the Low Pass Filter thread) and occasionally I insert attenuators between antenna & baluns. I enclose a PC screen of Radio Stations in the same frequency range as yours. The RSP-1A operated with Decimation = 16 in LOW IF mode and no MW filter inserted. My PC screen looks quite clean to me and I would like to have your comments as you seem to have quite a good experience. I tested every little carrier to check if it was IP3 or Higher Order, but found nothing.

I also wonder why you do not use the SDRuno software: it would be easier to cross check the PC screens back and forth with the same receiver software!

'73, glovisol
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glovisol
Posts: 269
Joined: Thu May 10, 2018 6:42 pm
Location: Piedmont, Italy

Re: THIS THREAD EXPLAINS WHY IT IS SO DIFFICULT TO UNDERSTAND RECEIVER'S SENSITIVITY IN LF & RELATED MATTERS

Postby glovisol » Sun Jan 13, 2019 4:49 pm

Hi again Bas,

Your WebSDR is FANTASTIC! Very deserved compliments!

glovisol

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ON5HB
Posts: 19
Joined: Sat Dec 29, 2018 1:07 pm

Re: THIS THREAD EXPLAINS WHY IT IS SO DIFFICULT TO UNDERSTAND RECEIVER'S SENSITIVITY IN LF & RELATED MATTERS

Postby ON5HB » Sun Jan 13, 2019 4:52 pm

Hi Glovisol,

Well I use the RSP1A's just for people that have no receivers themselves or no place to put antenna's, so they can run my receivers remote.
My own transceiver is an Icom 7300 that covers 0-72MHz with better numbers :D

Do not get me wrong, I love these RSP's but I use them for other people to listen on bands.

As you see on my websdr, it's many people use the 3 RSP1A's at the same time, it's not build for myself but for others.
My problem was people didn't believe my signal-reports, I have a server running anyway so let people check it out themselves.

Just want to share my location/reception with others, makes me happy if they enjoy it. :D

Thanks for the compliment :!: :!: :!: :!:

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