Recent content by stephenkearney

It took awhile but now I understand how the 1/4 wavelength matching section works! Here's a pretty good explanation: http://www.allaboutcircuits.com/vol_2/chpt_14/7.html And as mentioned earlier the PY4ZBZ fullwave has an extra 1/8 lambda added to each each arm to get a little more gain...

I did see a lot of discussion of the quarter wave stub for impedance transformation. The quote in my last message was about a slightly higher gain variation on the full wave dipole + quarter wave matching stub. The horizontal stub lines have currents moving in opposite directions. Those...

You're getting fantastic range! I'll never get anything close to that because our house is in a valley. I've been doing some research on the 'full wave' antenna. I think it's what is mentioned on this page: 5/8 wave for 1090 MHz is 172mm. I believe the 150mm dimension is the result of...

Hmm. It just occurred to me that this antenna is a 1 5/8 lambda dipole. That's a good wavelength multiple for dipoles, isn't it?

The 'height' drop-down control has 10m but not 9. At 10m the app claims 10.47 dBi gain.

I did run the Optimize function in MMANA GAL and it confirmed the dimensions. MMANA GAL shows 5.14 dB gain and 4NEC2 has it at just under 5 dB. EDIT: In MMANA GAL it's 5.14 dBi in free space. It's 9 dBi when 7 meters above real ground. .

I created a model in 4NEC2 and it seemed to work okay. Then I installed the MMANA GAL antenna modeling software so I could use the original model file. Looks like a nice antenna and easy to make too!

By the way, I don't understand the dimensions shown for the antenna. Why 150mm elements? The total length will be 150 + 150 + 8 = 308mm which is the wavelength of 975 MHz. Seems to me the antenna should be 275mm for 1090 MHz. http://www.onlineconversion.com/frequency_wavelength.htm .

So it's basically a full wave dipole antenna? According to this page impedance approaches infinity for full wave dipoles so some sort of impedance transformation would be needed; that's the horizontal section. I imagine that the feed point location is important for achieving 50 Ohm impedance...

What's the return loss at 911 MHz? If it's -18 to -20 around 918 MHz it can't be too bad at 911 MHz, can it?

I've been madly testing different ground plane designs; it's pretty easy to construct them out of paper with a layer of aluminum foil. Or thin aluminum sheet from cut up beer cans ;). However I've had trouble getting consistent results. I suppose it's due to the tiny values we're dealing with...

I think that scanner plug-in is neat but it doesn't have the spectrum analysis features that RTLSDR Scanner has. The return loss measurements are pretty easy. Basically I followed the directions in the How to measure return loss of a 978 MHz antenna video. Except I used the ADF4351 for the...

Some interesting results from my return loss testing: To get a lower physical profile I originally soldered the coax to the base of the antenna instead of using a BNC connector. That break in the coax shield resulted in a significant return loss. Now I'm making all connections with proper...

I have no problems with SDR# except the ~3 MHz spectrum display (which is actually a limitation of the RTL dongle). A return loss scan for a 1 GHz antenna would typically cover 50 MHz of bandwidth and with a 3 MHz window it's hard to do :) That's why I was trying to use RTLSDR Scanner -- it...

That's the thing... it doesn't sweep quickly. Each step (0.1 MHz in your settings) takes a few seconds to do. Like you, I expected it to be fast.... but it's not. I should have explained better. I understand how it's supposed to work, as seen in the How to measure return loss of a 978 MHz...