Overview

I recently bought this discone antenna for around 150AUD for general purpose SDR scanning use from the South Eastern Communications ebay Store here in Australia. It claims to have 25-1300MHz RX coverage, but the TX bands are limited to 49.5-50.5, 120-180, 215-300, 415-465, 610-650, 700-1000 and 1130-1300MHz, suggesting the SWR might be not so great in the in-between sections, which I confirm below.

It came with all the necessary parts and mounting tools, and the build quality seemed reasonably good. Assembly was straightforward - the disc radials are bolted securely, while the cone radials are kept in place using hex worm(?) screws which are not so great (don’t lose the tiny hex key when installing on the roof!). The connector is UHF female, i.e. SO239, which necessitates a PL259 to SMA converter. The mounting pole is hollow and fortunately large enough to fit an RTL-SDR.com dongle inside. This means no coax is needed, and you can simply run an active USB cable through the roof, removing any losses.

assembled antenna with RTL-SDR inside pole

Disaster strikes

One issue though: I noticed the connection between the antenna and the pole used 3x Phillips screws. Although there is a rubber O-ring which should prevent water from entering the top interface, it does nothing to prevent water entering through the screw holes. Anticipating this, I used some hot glue to seal all the edges (apparently not well enough…). I then installed the discone on the same mounting pole as the TV antenna, and all worked well for a couple of days.

A few stormy days passed and everything continued functioning. However, not long after this, I noticed extremely weak signal reception across all frequencies - even FM stations were barely visible. Taking down the antenna, it was clear that water had seeped in and run over the RF connectors and into the RTL-SDR. There was no visible corrosion but even after cleaning with isopropyl alcohol and drying, the SDR improved only marginally. IMPORTANT NOTE: cover the screws and joint with silicone sealant or similar to prevent equipment damage.

Performance

I used a NanoVNA-H4 to get a rough idea of the actual performance across the stated 25-1300MHz. The VNA was connected through a short SMA pigtail directly to the antenna. Due to the UHF connector, I could not exactly calibrate out the effect of the adapter, and had to use the ‘electrical delay’ feature to crudely adjust for this.

The sweep below is between 24-1100MHz. SWR is in yellow, 0.5/division. The notches seem to line up well with the stated TX bands. For my RX use, it doesn’t matter as much and is acceptable. The long centre antenna can be removed if you don’t need <50MHz reception. VNA

Real-world use

In the short time so far I have used this antenna to pick up airband from Brisbane Airport around 20km away, multiple pagers, APRS, AIS, CB radio and intermittent activity on the 2m & 70cm bands. I also received very grainy NOAA APT images using this antenna, which is more than I expected. This type of wide band antenna is also well suited for running rtl_power frequency scans, as shown below.

24-500MHz scan with 50kHz bins

Overall I am happy with the antenna and can recommend it. It would be perfect if the screws were also properly weather sealed.

RIP RTL-SDR.com dongle (2016-2021)


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