Signal generator

Between 1 and 2 GHz are aviation, radar, navigation, ham radio, cellular, hydrogen line, radio astronomy, satellite communications, maritime, radiometry, etc. You'll find the US allocations listed at: Pg 32 - 39. Which of these were you planning to jam?

Perhaps find something else to do?

Oops. I forgot to include the link.

>Pg 32 - 39. Which of these were you planning to jam?

1W?? Seems a *hell* of a lot for a sig gen!

jeff - this is for tuning an antenna for a gps reciever.

Hul

Jeff Liebermann snipped-for-privacy@cruzio.com wrote:

jeff - this for tuning an antenna for a gps reciever.

Hul

Jeff Liebermann snipped-for-privacy@cruzio.com wrote:

You don't need a whole Watt for that.

It is extremely antisocial to jam that band. Unless you are inside a Faraday cage so that there is no leakage of your signal to the outside world then you deserve to be prosecuted for doing it.

What is wrong with adjusting it to maximise signal strength from the satellites overhead? Even a few mW CW TX might blind nearby GPS devices.

+1

You should not be deliberately radiating RF into protected bands!

If you have a spectrum analyzer handy (or a SDR dongle and some free s/w), you can just point the antenna at the sun and tweak it up for maximum signal.

Cheers

Phil Hobbs

Nothing fancy in this frequency range. The plan was to use a handy Wavetek device but it's not working.

Hul

Phil Hobbs snipped-for-privacy@electro> > jeff - this for tuning an antenna for a gps reciever.

1 watt is far too much RF power for testing antennas. GPS signals are easily trashed by interference. For example, GPS was dead in the Moss Landing, CA harbor area because of an oscillating amplified TV antenna. My guess is about 10 milliwatts of RF power. When I work with small antennas, it's usually with low power, in a shielded building, in a screen room, or using a screened enclosure. This is as much to prevent interference to GPS (or other service) users, as it is to reduce interference from strong signals in the same frequency range or adjacent bands.

Kinda sounds like you're a hobbyist and are not going to buy expensive test equipment. So, a minimalist setup should suffice for GPS antennas. You probably want a VNA (vector network analyzer). I haven't tried this model, but it does go up to 3GHz and *SHOULD* work at GPS frequencies:

You'll also need some SMA connectors, cables, adapters, and terminations. About $60 and up.

I made the mistake of buying a NanoVNA V1 model clone, that proved to be junk. Avoid the clones unless you're sure that they work.

Also, no matter where you buy one, you will probably need to update the firmware.

I don't know what type of GPS antenna you're designing. Designs vary depending on how the GPS is used. For example, a hand held receiver will probably use a patch antenna. For fixed installations on rooftops, a wire antenna (quadrifilar helical) gives better gain near the horizon. For fixed locations, a ground plane will reduce ground reflections. For precision surveying, a choke ring reduces multipath and ground reflection problems, while maintaining an accurate phase center:

For antennas: Small size, high gain, wide bandwidth. Pick any two.

Good luck.

Yep, that works. However, I didn't want to setup an outdoor lab and limit my hours to when the sun is shining. Besides, I do my best work under cover of darkness.

The really cheap R820T2 SDR tuners will only tune up to 1766 MHz. That's sufficiently high for the GPS bands (1610 MHz max). However, I've seen receivers with poor sensitivity where anything above about

1GHz is buried in the noise.

I have two of these noise sources:

The output isn't very flat but works ok over narrow bandwidths. However, from 1100 to 1610 MHz frequency range needed for GPS, I the noise drops -5dB at the high end. For that, a spectrum analyzer with a normalizer feature is required. I cheat and just rotate the CRT trace against the grid.

Before the days of cheap VNA's, I used a return loss bridge:

It would directly indicate return loss or VSWR, but would not show whether the reactance was inductive or capacitive. That made tweaking antennas a bit of a challenge, but after a few mistakes, I could tell which direction I should tweak. Besides the bridge, all that was needed was an RF sweep generator with DC horizontal output, an RF detector (diode), DC log amp, and almost any oscilloscope. If all that is needed is the frequency of minimum VSWR, then a bridge is sufficient.