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Old 06-11-2017, 9:13 AM
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Default LNA/Portable antenna on the RSP2

I thought I would post on an experiment I did in the last couple of months.
With the availability of the 5V bias-T on the RSP2 I started looking at portable antennas and LNA modules.
One note, I am a technician (not class of license, just what I did for a living for too many years) not an engineer so the design can and should be improved by those with more knowledge than I.

I started with the basis of the Apollo antenna I found online https://apollo.open-resource.org/missio ... na-for-sdr.
The idea being to use what I had available and inexpensively obtainable.
For the tube, my garden shed had 2inch PVC pipe already on the rack. This is 2" inner diameter around 55mm. Good enough.
I obtained end caps at my local hardware store.
Copper foil for the antenna, many of the commenters on the Apollo site indicated they were having problems finding a source and the ones they found were pretty expensive. A search on the internet resulted in an Ebay seller: Copper Foil Tape - 6" X 10ft - EMI Conductive Adhesive / Ship from USA | eBay ... EBIDX%3AIT . Much thinner but also very inexpensive. Being in kind of a hurry and not feeling like re-engineering the foil template for the smaller diameter tube, I just used the Apollo template and curled it a bit tighter. I left the backing paper on the tape for insulation between layers.

Now to the magic
Low noise amplifier modules. I had played with some during my career but had no idea there were so many. Much searching and looking at spec sheets finally brought up ---- Ebay again. "What happens when I type Low Noise Amplifier in the box?"
I don't know how long this link will stay active 32dB 2Ghz 1-2000MHz Low Noise LNA RF Broadband Amplifier Module HF VHF UHF 6-12V | eBay is a 32dB 1Mhz to 2GHz LNA module with SMA connectors for less money than the components I had been finding. The module is rated at 6 to 12V. Hmmm 5V is just out of spec. A couple of weeks later, from China arrived my modules.

They are designed to use an external source of power but by-passing the output capacitor on the board allowed the RSP2's 5V to reach the proper lead on the chip.
I removed both the SMA connectors soldering the input side directly to the copper foil (with a bit of component lead cut off from another project) and a chassis mount F coax TV connector to the output side.
I am using RG6 for almost all of my receive only projects anymore and that eliminated an adapter.
A hole drilled in the center of one of the PVC end caps with the F female connector pushed through and secured, the copper tape rolled to fit inside the tube then unrolled and streched out to go end to end, I folded a small tab over the end of the tube at the top end and pressed the caps in place.

Smoke test time.
In town, the noise floor was killer, but turning the bias on and off allowed me to see the LNA was working. I was able to pick up WWV 5MHZ and see ADS-B 1020 chirps. All from one antenna.
What it was really built for is my trips to very RF quiet areas. High in the Rockies in South-Central Colorado I put the antenna on top of a 10' piece of mast that was attached to a ground rod driven about 5' into the very dry rocky ground, oh well it'll have to do.I put an F barrel connector at the base of the mast and used a gear-clamp to tighten the mast and shield of the cable to the ground rod.

Power up and all I can say is WOW. AM broadcast band.... well when the specs say 1MHz, they are being pretty optimistic but from about 1200KHz up things really picked up.
The HF utilities and SW stations were all there. Conditions petered out about 25MHz most of the time I was monitoring but no complaints from the antenna.
OK, FM broadcast band.. For years and many different portable and mobile radios I have played with meteor scatter in the FM band. I can usually get one or maybe two FM translators just above the noise to monitor and watch (since SDR) for pings. I now had 20 stations at or above noise floor. I was seeing aircraft reflections on stations. Many meteor pings and able to follow the times the ping happened with the waterfall.

Long first post but I would be interested to know if anyone else tries something like this.
I may have to go camping again

There was some thought to posting this in the Antennas portion of the forum, however I think a new broadband category may need to be added for the SDR antennas.

This antenna could also be used with any other SDR by using an power inserter or by powering the LNA module externally. A 9 volt battery would probably provide a full weekend worth of power.

Bruce
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Old 06-11-2017, 11:33 AM
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So what is portable for you?
In my case portable for me mean the diameter of a smal redbull canwho fit into my backpack.
And the first link dont work.
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Old 06-11-2017, 11:49 AM
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In my case, portable means will fit a go bag or padded case.
The antenna is approx. 20" end to end.
As well as it performs the dimensions probably can be cut down and still maintain reasonable performance.

The forum won't let me go back an edit the link, don't know why it truncated it the first time, so here goes again.

https://apollo.open-resource.org/mis...ntenna-for-sdr

Looks good on the preview.

For around $25.00 + items I had on hand. I am very pleased with what I came up with.
As I pointed out above, this is not an engineered solution. More experimentation is definitely called for.

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Old 06-11-2017, 12:33 PM
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I got an cheap Discone Antenna on ebay: https://sigmaeurocomm.co.uk/product/...ntenna-aerial/

Do you test the Antenna in an Urban environment like NY where a lot of noise is.
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Old 06-11-2017, 12:44 PM
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As I pointed out in the original post, in town the noise floor was excessive. This antenna is NOT a good choice for urban/suburban environments.
Discone antennas such as from ebay are basically only good from about 50MHz to 1200 MHz. They have no gain and therefore are great antennas for noisy environments. I was looking for an antenna that would perform in place of stringing a couple hundred feet of wire for HF work and multiple gain antennas for VHF/UHF.
The LNA in this antenna is rated 1MHz to 2GHz. That is why it was chosen and used. I wanted a "portable" antenna easy to erect at a remote site with a minimum of supporting infrastructure. For use at home, multiple antennas with specific jobs to do is the way to go.
For the record, if you look up my user name and posts, you will see that I have 3 discone antennas on my roof at home. I also have a small discone that mounts on a NMO mount for mobile use.

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Old 06-11-2017, 1:22 PM
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I will use the diconone for travelling. Can you store anything inside the tube?
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Old 06-11-2017, 1:25 PM
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At the risk of damaging components, no I would not recommend placing anything inside the antenna.
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