LNA/Portable antenna on the RSP2

Useful information regarding antennas for SDR products.
N0NHP
Posts: 1
Joined: Fri Jun 09, 2017 7:12 pm

LNA/Portable antenna on the RSP2

Postby N0NHP » Fri Jun 09, 2017 8:14 pm

I thought I would post on an experiment I did in the last couple of months.
With the availability of power 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: http://www.ebay.com/itm/152088504474?_t ... 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 :lol:
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 http://www.ebay.com/itm/282087141027 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. 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 :D

Bruce
Last edited by N0NHP on Thu Jan 01, 1970 12:00 am, edited 0 times in total.
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