Long-wire performance on different ports, bands

Useful information regarding antennas for SDR products.
franko
Posts: 15
Joined: Mon Aug 28, 2017 9:33 pm

Long-wire performance on different ports, bands

Postby franko » Sun Sep 03, 2017 4:38 pm

I've been experimenting with my new SDRplay RSP2 with SDRUno, using for now as antenna a 40-foot (12m) long-wire with a plain-wire lead-in and a ground connection via a ground rod.

On HF, with the antenna and ground attached to the RSP2's Hi Z antenna port, performance seems excellent in AM, CW and LSB modes. Performance also seems fine on VHF for FM signals such as NOAA Weather and FRS with the antenna and ground attached to the RSP2's antenna port A.

On the MW broadcast band, with the antenna and ground connected to the Hi Z port as for HF, the noise floor seems high and signals are hard to detect. If I detach the antenna, however, and leave only the ground wire connected to the gnd connector on the Hi Z port, the noise floor drops and signals of various stations appear very strongly. I assume that the SDRplay's front end had been getting overloaded, and the ground wire alone provides all the antenna that is necessary?

In the commercial FM broadcast band, with antenna and ground connected to Port A, I again see high noise floor and poor signals. However, if I leave the antenna and ground attached to Port A and use SDRUno's console to select antenna Port B (to which nothing is attached), the noise floor drops and the signals are very strong, with excellent stereo. I assume that again this is a situation where the SDRplay was getting overloaded. Are there internal connections between antenna ports A and B that would allow the scenario described above to occur?

In any event, I plan to continue experimenting with some different antenna designs including an active mini-whip, baluns, etc.
Last edited by franko on Thu Jan 01, 1970 12:00 am, edited 0 times in total.
Reason: No reason

someYguy
Posts: 46
Joined: Sun Apr 10, 2016 7:12 pm

Re: Long-wire performance on different ports, bands

Postby someYguy » Sun Sep 03, 2017 6:00 pm

Hi Franko,

I would recommend that you turn off the AGC (on the MAIN panel in SDRUno), and then use the IF Gain Reduction slider to manually adjust the overall receiver gain, also, try turning the LNA off and on to see which is best. These things should avoid most overloading. I've gotten to where I never use the AGC in the software because of such issues.

So, you should be able to connect your longwire antenna to the HI-Z port, tune to the MWBC band, turn off AGC & LNA, and then adjust the IF Gain Reduction slider for best signal/lowest noise.

Good luck!

Reason: No reason

franko
Posts: 15
Joined: Mon Aug 28, 2017 9:33 pm

Re: Long-wire performance on different ports, bands

Postby franko » Sun Sep 03, 2017 6:44 pm

Thanks for the suggestion. Initially I didn't see an AGC toggle in SDRUno's main panel, and no mention of it in the manual, but after clicking a button marked "SETT." a new window opened with a check box for IF AGC -- I assume that's it? I unchecked the box which caused a gain slider to appear, but no position of the slider resulted in decent signal levels.

As for the LNA, still looking for that.

I found, incidentally, why I was getting good AM broadcast signal levels with the antenna disconnected. It turned out that even though I'd disconnected the long-wire, I'd left a short (4 inch (10 cm)) wire attached to the Hi Z plug's P connector which I'd used to connect between the long-wire and the Hi Z port. Apparently this very short bit of wire is plenty adequate to pull in the local broadcast stations in my area. DX would be another story.

Reason: No reason

franko
Posts: 15
Joined: Mon Aug 28, 2017 9:33 pm

Re: Long-wire performance on different ports, bands

Postby franko » Mon Sep 04, 2017 1:24 am

franko wrote:As for the LNA, still looking for that.

I see from a tutorial video that SDRUno's main panel for the RSP1 has a prominent button for LNA. But I'm not finding it in SDRUno for RSP2. Has it been moved somewhere?

Reason: No reason

vk7jj
Posts: 15
Joined: Thu Mar 02, 2017 9:56 am

Re: Long-wire performance on different ports, bands

Postby vk7jj » Mon Sep 04, 2017 2:02 am

I see from a tutorial video that SDRUno's main panel for the RSP1 has a prominent button for LNA. But I'm not finding it in SDRUno for RSP2. Has it been moved somewhere?


The block diagram of the RSP2 shows the LNA is permanently in circuit when using Ports A and B and the only user adjustment is gain.

The Hi-Z port bypasses the LNA and goes directly to the MSi001 so there is no need to switch the LNA out in order to use that port.

The notch filter is switchable in/out but only when using A and B; like the LNA it is not in series with the Hi-Z port.

HTH

Edit: Try this video and all will become clear :-)

https://www.youtube.com/watch?v=w-vkiVp7Q4E

Reason: No reason

franko
Posts: 15
Joined: Mon Aug 28, 2017 9:33 pm

Re: Long-wire performance on different ports, bands

Postby franko » Mon Sep 04, 2017 5:01 am

Thanks much for the explanation -- very good to know.

Reason: No reason


Return to “SDR Antennas”

Who is online

Users browsing this forum: No registered users and 2 guests