RSP1A Longwave sensitivity

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Sabrina1984
Posts: 2
Joined: Tue Oct 30, 2018 12:19 am

RSP1A Longwave sensitivity

Postby Sabrina1984 » Mon Dec 31, 2018 5:58 pm

I am unable to get any usable reception below appx. 518 on my RSP1A. In the center of town I get MW mixing products but no LW signals; in the countryside just a blue screen. It works fine on VHF and HF. My antenna is a 160 ft. flat top with a 35 ft. down lead ... that works quite well on my NRD 525. I have tried various combinations of SR and DEC with no good results. I must be failing to make the proper adjustments and would welcome any suggestions.
Last edited by Sabrina1984 on Thu Jan 01, 1970 12:00 am, edited 0 times in total.
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g1hbe
Posts: 475
Joined: Sat Jan 17, 2015 3:28 pm
Location: Cheshire, UK

Re: RSP1A Longwave sensitivity

Postby g1hbe » Tue Jan 01, 2019 8:53 am

Try switching in the MW rejector. This will reduce the strength of any big MW signals which may be overloading the front end and masking the real LW stuff. Also try altering the RF gain and restricting the sample rate to (say) 200KHz. I have the RSP2 and it's as good on LW as any other RX I have.

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Andy

Roger
Posts: 217
Joined: Fri Dec 29, 2017 7:59 pm

Re: RSP1A Longwave sensitivity

Postby Roger » Wed Jan 02, 2019 12:59 am

The RSP1A does not perform as well on LF as the RSP2 and the RSPduo when using a poor antenna. This is because the RSP1A has a higher noise floor. See screenshots below (same antenna - an HF G5RV) That said you can still get some signals by doing the following.

1. Turn off the LO Lock and set to Low IF mode

2. Spin the frequency until the LO is at 1000 kHz and then Lock the LO

4. Turn on the MW filter. Check IF AGC under SETTings in Main window. Adjust RF Gain to max (Attenuation to minimum). If you get AD overload you need to reduce gain (add attenuation) However this will increase the noise floor of the receiver.

5. You can use the zoom feature to show only the signals below 500 kHz.
Attachments
RSPduo HiZ.PNG
RSPduo HiZ.PNG (114.42 KiB) Viewed 2584 times
RSP1A.PNG
RSP1A.PNG (105.91 KiB) Viewed 2584 times

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glovisol
Posts: 637
Joined: Thu May 10, 2018 6:42 pm
Location: Piedmont, Italy

Re: RSP1A Longwave sensitivity

Postby glovisol » Wed Jan 02, 2019 6:14 am

This thread and referenced material should help.

viewtopic.php?f=11&t=3936

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g1hbe
Posts: 475
Joined: Sat Jan 17, 2015 3:28 pm
Location: Cheshire, UK

Re: RSP1A Longwave sensitivity

Postby g1hbe » Wed Jan 02, 2019 9:06 am

Wow Roger, I didn't realise the 1-a was so far behind the other models at LF. I wonder why this is? I find my RSP2 is very good all the way down into the VLF range, although it does need a 100 kHz LPF to keep out LW images.

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Andy

glovisol
Posts: 637
Joined: Thu May 10, 2018 6:42 pm
Location: Piedmont, Italy

Re: RSP1A Longwave sensitivity

Postby glovisol » Wed Jan 02, 2019 11:19 am

Hi g1hbe and Roger,

This apparent low sensivity of the RSP-1A looks very strange to me as well.

I am away from home but next week will be able to make a comparison between RSP-1A and RSPduo. In the meantime, if we look at the published specs, the RSP1A sensitivity on the 2200 m bands appears slightly better than that of the RSPduo, as follows:

RSPduo: AM-6.16uV / SSB-2.29uV / FM-5.36

RSP-1A: AM-6.02uV / SSB-2.26uM / FM-5.01

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Murphyv310
Posts: 9
Joined: Mon Aug 13, 2018 8:55 pm

Re: RSP1A Longwave sensitivity

Postby Murphyv310 » Wed Jan 02, 2019 2:01 pm

Hi.
I have to say that my RSP1A works very well indeed right down to 60kHz. For a while I used a CR100 receiver with a modified Front end with two EF95 pentodes as the RF amplifiers. I use a modified Wellbrook loop and have had some excellent DX. Initially I thought the RSP1A was overly noisy and low gain but with careful setting of attenuation, IF and bandwidth it out performs the CR100. Bear in mind too that monitors and the PC generate noise which greatly effect low frequency reception which may be another reason for poor results. I've also found that the MW notch also has effects on LW especially in the broadcast band section so if you use a long wire an ATU may be an idea. Ideally if you have the space erect a Beverage aerial, one of my mates has one and on his Perseus Sdr it is awesome, will need to try the RSP1A on it some day.

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Cheers Trevor :D

Roger
Posts: 217
Joined: Fri Dec 29, 2017 7:59 pm

Re: RSP1A Longwave sensitivity

Postby Roger » Wed Jan 02, 2019 7:12 pm

g1hbe wrote:Wow Roger, I didn't realise the 1-a was so far behind the other models at LF. I wonder why this is? I find my RSP2 is very good all the way down into the VLF range, although it does need a 100 kHz LPF to keep out LW images.

gihbe,

The RSP1A will work down to 1 kHz. but was not optimized for operation in the VLF, LF and MW bands. It only has one input and not three like the RSPduo and RSP2. The HiZ port on the RSP2 and RSPduo has better performance below 30 MHz. because it uses a different front-end RF and mixer section on the Mirics chip. You can really see this when operating under 2 MHz. Below you will find three screenshots which show the noise floor on LF for the different models. In all cases maximum IF and RF gain was used and all inputs were terminated with a resistive load. The MW filter was turned off for these tests. Spurious signals and high-order mixing are an issue for LF operation and using Low IF (instead of Zero IF) helps somewhat. Reducing the RF Gain actually adds attenuation and increases the Noise Figure (NF) of the receiver. External MW rejection filters, proper antenna selection and the use of a preselector will improve reception with any of these RSP devices.
.
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Attachments
RSPduo Noise Floor 1.24.PNG
RSPduo Noise Floor 1.24.PNG (272.17 KiB) Viewed 2499 times
RSP2 Noise Floor 1.24.PNG
RSP2 Noise Floor 1.24.PNG (283.49 KiB) Viewed 2499 times
RSP1A Noise Floor 1.24.PNG
RSP1A Noise Floor 1.24.PNG (267.74 KiB) Viewed 2499 times

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sdrom33
Posts: 120
Joined: Sun Dec 09, 2018 4:38 pm

Re: RSP1A Longwave sensitivity

Postby sdrom33 » Wed Jan 02, 2019 8:18 pm

Hi z inputs cannot be compared with 50 ohm in of rsp1a. Better compare 50 ohm of all sets to have best idea.
Last edited by sdrom33 on Thu Jan 01, 1970 12:00 am, edited 0 times in total.
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arcosine
Posts: 30
Joined: Wed Jan 02, 2019 6:24 pm
Location: 41.678472, -88.051762

Re: RSP1A Longwave sensitivity

Postby arcosine » Wed Jan 02, 2019 9:26 pm

Hi,

I have a RSP1A, for about a week. I works OK on LW. WWVL is strong. I have a 700 ft wire antenna, grounded at the end. I made an impedance matching transformer which helped a lot. The antenna is high impedance, which was a surprise. I also have a parallel tuned circuit that I wound on the matching toroid, which helps it from being overloaded from AM broadcast, 1160 which was 60 over S9 on my Yeasu ft450D, 40 miles away. You could try a low pass filter, or add inductance to the antenna. The CubicSDR program, though leaves a lot to be desired.

Tony
Last edited by arcosine on Thu Jan 01, 1970 12:00 am, edited 0 times in total.
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Tony
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