HF pre-selector

Useful information regarding antennas for SDR products.
NN4F
Posts: 128
Joined: Fri Apr 03, 2015 1:54 pm
Location: Ridgeville, SC
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Re: HF pre-selector

Postby NN4F » Sun Oct 11, 2015 3:45 pm

One of the best I ever found for SWL was the Global AT-2000, sadly no longer made, but you may be able to find one used
it works extremely well, or now the MFJ1046 is similar...

Paul - NN4F
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--
Paul Jones - NN4F, Charleston SC
http://www.facebook.com/groups/SDRPlay

CaptainNemo
Posts: 140
Joined: Mon Jan 05, 2015 1:22 pm
Location: Genoa - Italy

Re: HF pre-selector

Postby CaptainNemo » Mon Oct 12, 2015 2:02 pm

By the way, "DM4070 LCR meter" could be an honest tool for the price?
(about 40-50 $ on e-bay)
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m0phe
Posts: 7
Joined: Thu Aug 13, 2015 6:54 pm

Re: HF pre-selector

Postby m0phe » Sat Oct 17, 2015 11:08 am

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ptuton
Posts: 1
Joined: Wed Oct 28, 2015 5:10 pm

Re: HF pre-selector

Postby ptuton » Wed Oct 28, 2015 5:28 pm

I use this one and find it excellent. Takes very little building.
http://www.lz1aq.signacor.com/docs/RF_p ... lifier.htm

With HDSDR or SDR-CONSOLE 2.x, the SDR-PLAY is now my favourite HF general coverage Rx. (One of the alternatives is an AR7030).

..
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CaptainNemo
Posts: 140
Joined: Mon Jan 05, 2015 1:22 pm
Location: Genoa - Italy

Re: HF pre-selector

Postby CaptainNemo » Tue Nov 24, 2015 1:50 pm

Thank you very much to all. I get a lot of ideas from this forum.
I'll try to build a preselector by myself.

By the way. Yesterday I was looking for info about "usb galvanic isolator" and suddenly I found a cheaper solution.
I moved SDRplay from one usb port to the near one, a lot of "vertical lines" disappeared. Great!
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vk3zfs
Posts: 1
Joined: Sun Dec 27, 2015 1:22 pm

Re: HF pre-selector

Postby vk3zfs » Thu Dec 31, 2015 5:22 am

My gathering dust Yaesu FRG-7, might be put back into service as MF-HF RF pre selector, new life for a old boat anchor :)
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WB5AGF
Posts: 7
Joined: Sat Feb 17, 2018 6:35 am

Re: HF pre-selector

Postby WB5AGF » Thu Feb 22, 2018 4:05 am

Dear Captain Nemo (may I please get a ride on the Nautilus sometime ?);

A long time ago the ARRL Handbook had a 'regenerative preselector' for the HF bands. Given the era (1960s) it was based on vacuum tube technology but still .... a very interesting idea .... (as a regenerative amplifier is brought near oscillation the effective bandwidth begins to narrow very significantly)

I live only 4.3 miles from the antennas of KRLD (50 kW on 1080 kHz) and listening to anything near that portion of the AM Band can pose problems.

So far I have only been considering how to combat the tremendously strong signal coming from KRLD but I have been thinking significantly about a regenerative preselector (with variable coupling to keep signal levels under control).

Regards;

Paul, WB5AGF
Texas
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vk7jj
Posts: 43
Joined: Thu Mar 02, 2017 9:56 am

Re: HF pre-selector

Postby vk7jj » Thu Feb 22, 2018 10:28 pm

To add to Tech_Support's suggestion of using a "ham" antenna tuner, I use an old antenna tuner (commonly known as an ATU) but instead of connecting it in series with the feedline, I use it as a tuneable shunt to ground.

If the ATU is simply inline as normal then it works fine but it only passes the relatively narrow band of signals it's tuned to. The problem then is you have to retune it all the time when changing frequency or changing bands even if it's only a relatively small change.

If the ATU is connected as a tuneable shunt to ground then it gets rid of the unwanted band of signals it's tuned to and passes everything else.

The one I use is good for the amateur bands from 160m to 10m and I found in practice that as a shunt it can be adjusted to be narrower or broader so as to "notch out" the broadcast band without bothering 80m, or be more finely tuned to wipe out a particular broadcast station. It also works well in taking out bands of noise anywhere on the HF spectrum

If you have access to a spare ATU, especially an older bulky manual one whose owner has moved to nice shiny new automatic thingy, then have a go. The older and larger the ATU the better it's likely to perform. The one I'm using is an old MFJ with a roller inductor.

Put a T piece in the coax between the antenna and the RSP1a, connect the 'radio' connector of the ATU to the stem of the T piece and put a short circuit across the 'antenna' connector of the ATU, and have a play. In fact have an SDRplay :-)

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