Hot Rodding a Power AIM

[davedybas]

Broadcast Consultants use expensive HP Network Analysers along with 100 watt linear amplifiers and other gear to overcome the inherent co-channel interference when tuning up AM broadcast station antenna tuning units.  The Power AIM and other AIM products are equally as accurate as the $$ HP Network Analysers but lack the high level RF signals that Broadcast Consultants use to overcome the interference.

Now I know it isn't possible for Bob Clunn to manufacture a product that puts out similar levels of high power RF,  but it sure would be nice if maybe he would offer a bit of advice on how to "hot rod" one of his VNA's to be competitive with the expensive HP setups.   All a person would need is about 5 VPk-Pk at the output of the AIM to overcome interference.


Just an idea.....  

[Bob]

That could be an interesting project.

I would like to get ideas for new features to incorporate in a new version of the PowerAIM.
Is 5V peak to peak enough in the BC band? How much is needed in the FM band?

73/Bob

[davedybas]

Hi Bob,

I'm not sure about the level necessary to keep interference out in the FM Band.  Each FM site is different, some sites have several FM stations operating from a common tower/structure.  I will check with my buddy the RF Engineering Consultant and see if he has an idea of how much signal it takes to overcome other stations in a common site.   Will let you know what I find out.



Best Wishes,

Dave Dybas 

[Burt]

Hi Dave & Bob,

The measurements techniques you're referring to requires at least a two port Network Analyzer. The RF output of the Network Analyzer feeds a RF amplifier, such as an ENI 310L, which has approximately 50 dB of gain and can increase the RF output to approximately 10 watts, although some amplifiers can increase it to several hundred watts. The higher power output is then used to drive a return-loss bridge (RLB) capable of handling the power, with the device under test, usually an antenna, connected to the unknown port. The return port is then connected through an appropriate attenuator back to the receive port on the Network Analyzer. The advantage of doing this is that when you are in a high RF environment you reduce the desired to undesired signal/s in dB by the amount of the attenuator you put in between the RLB and the receive port of the Network Analyzer.

The problem, as I see it in using the Power AIM-120 is that it's a single port instrument, so I don't see how you could use it in the manner described above.

What I think I'd like to see is a version of the AIM-2180 intended to work with an external RLB with the RF power handling capability of the Power AIM-120. If my thinking is correct, you could then add the external RF amplifier and the appropriate attenuator to the receive port. I don't think it's quite as simple as just building a high power version of the AIM-2180. Normally, the 2180 is fine for handling filters and such that are not connected to an antenna in a high RF environment such as Mt. Wilson.

I will tell you that I've had good success using the Power AIM-120 to make meaningful measurements on FM antennas at Mt. Wilson. These were not antennas in the densest area of Mt. Wilson (Mt. Alta), but antennas about a 1000-feet away. Yes, I was very concerned about the amount of RF that might be coming back into the Power AIM-120, but to my utmost darned amazement, it worked very well. That said, if you plan on using a Power AIM-120 in a high RF environment, use caution. I'm not sure how much RF a Power AIM-120 can swallow before it becomes destroyed.

Burt

[mel]

While I am no BC engineer, in the past, when needing to make reasonable RF measurements within a mile of a HP BC transmitter, I was able to make a reverse duplexer.  That is, antenna under test on the common port, LP to a HP 50 termination and the HP to the measurement device for 1.8 MHz and above.  Just a comment on one aspect of using the VNA.


Mel, K6KBE

[smokchsr]

So far I've been able to measure pretty much everything with the power AIM as it is. When I do get into the noisy environments, I'll use the highest averaging value and a very low step rate, even down to 1hz. Yes, it takes a bit longer but I've been able to get nice clean graphs in congested areas even at night.
A bit more tickle power would be nice, but at least so far I've been able to get good clean data.