Message posted by lone wolf on July 13, 2005 at 21:34:08 PST:

I can't say for sure you will hear mil air in the Nellis ranges from Cedar City, but looking at the map, it does not look impossible. The trouble is there are long gaps during the day when you won't hear much UHF (unless of course you can hear a military tower). The Nellis exercises run for about two hours at a time. Much of the Nellis traffic is VHF, but in that odd band of 138 to 142 MHz. The AWACS is always UHF, but it is not routinely in use except during Red Flag. You can't expect the mil air band to be all that busy unless you are close to a base.

Most radios are rated for sensitivity. [Uniden doesn't have published sensitivity specifications, so I suggest not getting their products unless all you are going to do is monitor near a base, i.e at an air show.] The lower the number, the more sensitive the radio. The SNR is an abbreviation for "signal to noise" ratio. There are some nuances on how it is measured, but the effects of these nuances is pretty minor and not worth the 3 paragrahs I'd have to spend explaing them. The idea is for the same SNR, the radio with the lower number wins. Thus a radio with 0.5uV sensitivity can receive a signal that can't be heard on a radio with 2uV sensitivity under extreme conditions.

I don't have the data handy on the Pro-95, but I recall it wasn't very good in mil air. [Don has the data.] Remember, it was not designed to receive mil air, so why would you expect it to excell on mil air.] The Pro-96 has a sensitivity of 2.8uV at the worst location in the mil air band, so it's not so hot either.

To put the radio sensitivity in perspective, you can compute the distance required for each radio to receive the same signal. [Sorry, this will require some math.] Lets say I have a MVT7100 picking up a signal from 100 miles, and the antenna delivers 0.5uV. Now suppose I have another radio that has 2uV sensitivity. We use the same transmitter and antenna. If I was positioned 50 miles from the transmitter, i.e. half the distance, the signal would be 4 times as strong. This is known as the square law. [4 x 0.5uV = 2uV] Thus a Yupi MVT7100 can hear a signal 100 miles away, while the less sensitive radio has to be a whopping 50 miles closer to hear the same signal.

Now to a certain extent, you can improve this with a better antenna, though after a while, the radio will overload. It's really hard to get gain over a wide bandwidth such as mil air (225 to 400Mhz). However, it can be done with a log periodic antenna cut for the band. This is where the AS-1405 comes in. They show up on ebay and at Murphy Surplus in San Diego. I paid $125 plus shipping for one and was happy. I found one at a flea market for $20 and didn't complain. It's worth the search. The antenna is no longer manufactured, so all you can do is get them as the military upgrades. The current mil air log periodics are from Taco:

http://www.tacocommunications.com/lpdfeatures.htm
Look at the smaller antenna, which has a gain of 8dbi. A dipole (similar to what you probably use on your scanner) has a gain of about 2dbi. Thus going to the log periodic gets you 6db more power, which is a ratio of two in voltage. It's an improvement, but in this example, going to a more sensitive radio is better. In fact, you would need a 12dB improvement in the antenna to be on par with the improved radio (0.5uV versus 2uV).

Note that the dipole gain of 2dB assume it is resonant at the frequency in question, so it can often be much less gain. The log periodic is resonat over a wide bandwidth, so you really do get teh 8dbi.

The other choice is a discone. These can be a real pain in the arse if you have FM broadcast stations and TV stations nearby, as this overloads the scanner. There is a military discone, AT-197/GR. They range from $45 to $100, depending on who is selling them. While they have no gain, they are wide bandwidth, so the antenna is actually working over the mil air band. I know someone bidding a contract to replace these antennas for "an undisclosed air base" and may be able to scare up a few used ones. [No promises, but I'll post it here if Joerg approves.]

In Reply to: Re: military/area51 frequency questions posted by joe inman on July 13, 2005 at 17:18:00 PST:

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