Topband: Beverages

[Tom Rauch]

I just measured some signal levels this weekend, so I'll post a few 
of the levels because other may be able to use the information to 
estimate signal levels they might have in their antennas.

> you can hear noise on an unmatched beverage, is there any resulting
> benefit in signal to noise ratio by having a proper match or would it be
> the same effect as adding a preamplifier when one is not needed?

Once you clearly hear external noise, amplifiers or impedance 
matching won't help. Just be sure you can hear noise at the 
quietest time you expect to operate.
 
> 2.  Can we anticipate big problems using these receiving antennas on
> multiple bands in the multi-multi category if we do not have filters,
> splitters, etc. in the receiver antenna lines?

There are too many variables to answer that question. Receiver 
quality, spacing to transmitting antennas, and the efficiency and 
pattern of the antennas all matter.

Here are some signal levels in my system with 100 watts applied 
to a 200 ft omni-directional tower with 100 200ft long radials, and 
matched Beverages with no amplifiers. Add ~11.8 dB and that will 
be the level with 1500 watts, or subtract 50 dB and that will be the 
system loss between the two antennas.  

Distance 300 feet, Beverage aimed 45 deg off from the vertical +22 
dBm. (That's a LOT of signal level! It would be over two watts of 
signal into the receiver with no pre-amp and 1.5kW transmitter 
power.)

Distance 800 feet, Beverage aimed away from the vertical +6dBm.

Distance ~2000 feet away, Beverage aimed towards the vertical
-3.5dBm. Beverage aimed away from the vertical -18.5dBm.

If you don't have some real distance, you'd better have some stout 
preamplifiers and filters if you plan on multi-band operation.

73, Tom W8JI
w8ji@contesting.com


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