Beverage Antenna

[K9ACT]

My 600 ft Beverage antenna is up and running but I am not totally satisfied that it is working as it should nor do I exactly understand how to prove that it is set up right.

I started out with a 600 ohm wire wound termination resistor.  Info out there is rather conflicting.  One person spends a whole page describing the whys and wherefores of non-inductive resistors.  Another says it makes little difference at the freqs we are dealing with.

My only evidence that it works is that a few stations I have heard on 160 are vastly easier to copy using the antenna than with the transmit antenna.  However, most stations sound about the same  and none sound better on any other band but 160.

The instructions on one web site and the ones that come with the MFJ antenna analyzer simply say to adjust the resistor to show a constant SWR over a frequency range.  The absolute value does not matter.

It is not clear what the frequency range needs to be for the test nor what is meant by a constant range.

I see a change from 2.6 to 2.1 to one from 1.7 to 4 mHz.

I have tried resistors between 300 and 700 Ohms and there are some dips  over the range but I don't know if it's because of the type of resistor or the value.  The 600 Ohm shows no dips just the slow change over the range.

I bought some non-inductive resistors today and they don't seem to make any difference and work about the same as the ones I was using.

It is also interesting to note that only one of the 3 values of non-inductive resistors indicates X=0 on the MFJ.  The other two are about the same as the wirewound ones, between 150 and 200.

I have a 50 ohm mud resistor that reads X=0 and the dummy load in my tuner reads about about 5.  Is this a valid test for non-inductive resistors?

So, any help here will be appreciated,

js

[K1JJ]

I wouldn't worry about swr for now - at least until the f-b is adjusted.  The terminating resistor is primarily used as a front to back pattern generating device, not necessarily for feedline matching, though it will have an effect on the impedance. But absolute impedance doesn't matter as long as it's matched properly as a last step.

Use a reference dipole that favors both directions of the bev (or a omni-vertical) and adjust the resistor for maximum f-b on the beverage.  Do receiver A/B switches using on-air signals until you are satisfied the beverage shows a difference of at least 15-25db f-b.

I once set up remote resistor tuning and found my 600' beverage wanted to see about 400 ohms for max f-b. Your bev could be different, but there is an optimum value. THEN, after the f-b is maximized using the resistor adjustments, adjust the turns ratio on your matching transformer for the best match/swr to your feedline.

Yes, use a non-inductive resistor - no wirewounds. No sense adding in inductive reactance to muddy up the system.  Though, I have seen Huzman use an inductor to improve/tune the f-b of a shortened bev.      600' is about 1/2 the size for 160M use, so maybe if you cannot obtain a good f-b, you can then look to inducctor tuning - but as last resort.   On 75M, 600' is a great length for normal use and tuning with a resistor.

Hopefully the bev is no higher than about 7' on average above the ground.


BTW, the "reasonable" swr range on my beverages here extends from 160 to about 40M - pretty broad.    Using a terminating resistor or not has little effect on the range.

If you don't want to bother tuning for max f-b, then just insert in a 450-500 ohm non-inductive resistor and be done with it. (Match the feedline, of course)  You will see reasonable f-b.


Hope this helps.

T

[k4kyv]

To avoid surface traffic like people, cars and riding lawn mowers, I put mine up about 10' above the ground, although in some places, it sags to about 7' between supports.  I don't think I sacrifice much performance on 160, but I probably do a little on 40, but it's something I've never worried much about.

I used to have a single 10w 500-ohm mud resistor I used for termination, until a lightning hit vaporised it.  Somewhere, I came across a shoebox full of 2-watt 56Ω carbon composition resistors, so I made up a new one by wiring 9 of those in series.  I could use series-parallel combinations to come up with about any value of resistance in that vicinity.

The purpose of the SWR check over a frequency range has nothing to do with matching the feedline to the antenna.  For best F/B ratio, you want the terminating resistor to match the effective transmission line impedance formed by the beverage wire and the earth.  For a typical beverage, that is usually about 500Ω, so I just guesstimated and used that value.  If you have an exact match, the SWR should be constant regardless of frequency, just as with any other transmission line working into a matching load.  So the idea is that if the SWR on the beverage wire as indirectly indicated by measuring the SWR at the output of the impedance transformer or at the receiver end of the transmission line, does  not change as you vary the frequency over an octave or two, that the beverage wire is properly matched to the terminating resistor.

My matching transformer was designed to match 500Ω to 75 ohms, but if the terminating resistor is correct, I could just as well use a long run of 50-ohm coax between the receiver and the beverage transformer at the end of the wire, and it wouldn't make any perceptible difference, and it wouldn't matter if the surge impedance of the terminated beverage turned out to be 600Ω or 350Ω, as  long as it was properly terminated.