Performance increase question

[Singularity35]

I'm looking to raise my antenna to twice the height it is now, how much performance increase am I looking at?

It's a VHF setup BTW, it's at 40 feet, planning to add 40 feet more.

Thanks in advance.

 

[GnG8d]

Expect your angle of radiation to lower, and your gain to increase. That's about all can be said outside of your specific install.

 

[Singularity35]

Expect your angle of radiation to lower, and your gain to increase. That's about all can be said outside of your specific install.

Thanks, but can you please repeat that like you're explaining to a retarded child?

I'm really not after specifics, just in general. Also, is the additional 40 feet more beneficial than just running, say a 160 watt amp?

 

[GnG8d]

Thanks, but can you please repeat that like you're explaining to a retarded child?

I'm really not after specifics, just in general. Also, is the additional 40 feet more beneficial than just running, say a 160 watt amp?

Well, the higher you place that antenna, the more of the horizon the antenna can see "in general".

I'd raise the antenna and then think about an amp.

 

[Singularity35]

Well, the higher you place that antenna, the more of the horizon the antenna can see "in general".

I'd raise the antenna and then think about an amp.

Thanks.

 

[Mudfoot]

It's a VHF station he is talking about.

 

[W5LZ]

I think you will definitely hear a difference. No way I'll try to say how much difference, but there will be one. The same also applies to the guy on the other end, he'll hear some difference too. That's just from the differences in height.
As for power, that's just not all that important at VHF/UHF bands. It really is 'line of sight' up there, that's the biggy. So is the mode you would be using. Power certainly can make a difference (some) when using SSB or AM, but not much with FM. FM is an 'all or nothing' type of thingy, not like SSB/AM where signal strength increases can be heard. Considering the dollar/watt cost at VHF/UHF frequencies, it ain't gonna be cheap to hear a measurable difference at times (more of that SSB/AM/FM thingy). Spend the same amount of money on the antenna and there will be a measurable increase in what's heard.
Have fun.
- 'Doc

 

[KC9Q]

You add 6 dB whenever you double the antenna height. You will improve the receiver performance by double (i.e., a 1 microvolt receiver will perform like a 0.5 microvolt receiver). Your 100 Watt transmitter will act like a 400 watt transmitter. This does not account for cable losses which will reduce the figure a bit. The next best thing to do is getting a higher gain antenna. This is an old Motorola guideline.

 

[GnG8d]

You add 6 dB whenever you double the antenna height.

That's pretty profound, can you quantify it?

 

[Singularity35]

Thanks for the replies. Nice to hear.

 

[w9cll]

VHF is all about height so the higher the better.

 

[Singularity35]

Too bad I'm in the lowlands. A few buddies are way up in highlands and their 10 foot poles outdo my 40 foot one. :redface:

 

[The DB]

You add 6 dB whenever you double the antenna height. You will improve the receiver performance by double (i.e., a 1 microvolt receiver will perform like a 0.5 microvolt receiver). Your 100 Watt transmitter will act like a 400 watt transmitter. This does not account for cable losses which will reduce the figure a bit. The next best thing to do is getting a higher gain antenna. This is an old Motorola guideline.

6 dB whenever you double antenna height at VHF? That sounds a bit optimistic, actually that sounds very optimistic...

Lets see if modeling backs up the claim...

For this test we have a 2 meter 1/4 wavelength antenna measured at 1, 2, and 4 wavelengths high over average ground to test the 6 dB gain every time you double height claim...

So doubling height from 1 to 2 wavelengths high nets 1.7 dB in gain, and going from 2 to 4 wavelengths high gets you an additional 1.27 dB in gain. I have doubled the antenna height twice and only see 1.97 dB total gain. There goes the 6 dB gain every time you double the height idea...

Just to make sure being to close to the ground is not the issue here lets continue this some more...

Here we see 8, 16, and 32 wavelengths high. For a point of reference for those of us who use the imperial measurement system, 32 wavelengths at this frequency is over 200 feet high. That is beyond the height most people will ever get with such an antenna...

The peak gain of 6.49 dBi is only 4.01 dB in gain over an antenna mounted significantly lower than that antenna. Further, the next doubling of height results in a pretty significant drop in gain and a noticeably higher take off angle... Apparently, in this case, to much height is a possibility...

Further, it was stated here that there would be a difference in the transmit and receive gains. The Reciprocity Theorem disagrees with that assessment completely.

You claim that is a Motorola guideline? I've never heard of it, any reference to back that up?

The gain you get from increasing height at VHF is more to do with clearing obstacles and, as has already been stated...

Well, the higher you place that antenna, the more of the horizon the antenna can see "in general".

The DB

 

[Singularity35]

I'm confused now...

So there's not much benefit going from 40 to 80?

 

[The DB]

Additional height benefits you in two major ways, it allows you to clear obstacles, and increases the distance to the "visible horizon". How much that will benefit you depends on the natural and man-made structures in your area.

For example, if you are in the valley of a mountain range and the added height of your antenna still does not clear the nearby mountains it won't get you much. However, if you can raise the antenna above the mountain peaks it can make a world of difference. You may still have trouble communicating with those in neighboring valleys however, unless they have something like a repeater at the top of a mountain.

There is no easy cut and dry way to determine how well the added height of your antenna will benefit you. You being in a hilly area the benefit you see will be governed by the new height of the antenna verses the height of the hills/mountains in your area. The big question is does the antenna clear those hills/mountains or not.


The DB