Antenna Analyzer advice wanted- Which one should I Buy?

[prcguy]

If your using six of the large 1/2" ID 31 mix beads you might have between 600 and 900 ohms of impedance on the higher bands and a really good common mode choke will have 10-15X that. In attenuation speak you might have up to 15-18dB of common mode attenuation and there are chokes out there that exceed 40dB.

Thank you prcguy. That is the information I needed to expand upon for upcoming projects. I use six mix 31 beads on LMR-400 coax for the hexbeam. Now and I am curious if things can be improved there. Not that I am noticing any problems now. For my inverted V OCF I have a 150' run of LMR-400. I have not observed a difference with or without an RF choke on that. Also, thank you for the balun testing information as well. I have a few to test.

Thank you Fred for those part numbers and details. That saved me plenty of time and effort.

At this point in the hobby I am at 1.2GHz and down. VHF/UHF contesting allows me to analyze different antennas at different locations via QSO. Beacons are also quite helpful.

 

[freddaniel]

Jay raises a good point regarding the short. It has been my experience almost any short works OK below 1 GHz. However, when using a quality SMA short on an SMA to type-N adapter, the adapter must add some reactance to the mix as the SWR changes from a pure short. Therefore, the issue is uniformity over a broad frequency range.
The same issue applies to the 50-ohm load. It is not the precision of the resistance to 50 ohms, it is the uniformity of the impedance over the frequency range of your antenna analyzer. After all, a 75-ohm resistor would only yield a 1.5 SWR on a calibrated analyzer. For example, if you calibrate with a load that has poor SWR above 2 GHz, then any test above 2 GHz is going to be in error. Even a precision 50-ohm load will show a false high SWR above 2 GHz. Garbage in, garbage out.
In fact, precision mismatch loads are available just for the purpose of verifying your analyzer. I prefer to use an unterminated Narda 575 precision 6 dB or 10 dB attenuator, which yields 12 or 20 dB return loss respectively. The Narda attenuator frequency response is flat from DC to 12 GHz within 0.1 dB, so the impedance is also flat. These are available on eBay used for around $10.
The moral to the story, testing above 1 GHz requires better cables and the best adapters, otherwise you are introducing error into your measurements. Always verify after calibration.

 

[vagrant]

If your using six of the large 1/2" ID 31 mix beads you might have between 600 and 900 ohms of impedance on the higher bands and a really good common mode choke will have 10-15X that. In attenuation speak you might have up to 15-18dB of common mode attenuation and there are chokes out there that exceed 40dB.

Thank you for that information. I am unsure if I have previously asked, but what are you using with your heaxbeam and where along the coax did are you using the common mode choke? My beads are just below the connection, per the instructions.

 

[speedway_navigator]

I prefer to use an unterminated Narda 575 precision 6 dB or 10 dB attenuator, which yields 12 or 20 dB return loss respectively.

thanks for the tip, I'll add that into line sweeping class at IWCE.

 

[prcguy]

I don't remember what I used on my Hexbeam but it might have been 12 turns of RG-142 coax on an FT-240-43 core. Seems like I used dual cores but I can't find a good formula that covers 20 through 10m with two cores right now. I placed the choke right at the feed point of the antenna.

Thank you for that information. I am unsure if I have previously asked, but what are you using with your heaxbeam and where along the coax did are you using the common mode choke? My beads are just below the connection, per the instructions.