-1/4 wave 10m antenna showing usable bandwidth from 26.5-31.5 mhz

[mr_fx]

So a friend of mine wanted to get on 10m and was looking for an antenna, so I looked in my junk box to see what I had

-5 foot section of 3/4" galvanized EMT conduit
-one, A99 radial
-and a99 3/8-24 fitting
-ratshack plastic project box,
-some scrap PVC
-so-239
-some braided copper ground straps

well put everything together and added 4 wire radials, they where a bi long, about 9 foot, they are tied into a tree at ABOUT 45 degrees, plus or minus a bit, either way sloped pretty well

the emt is at the base, the A99 radial is on top of the EMT and cut to correct length and the center of he coax goes to it, the coax shield goes to the radials and every thing is isolated from the mast by the PVC

when checked at the feed point with a MFJ-259 it shows the resonant point to be around 28.4Mhz 52ohm, 1 Reactance, 1.0SWR

it shows a 2.0 swr at around 26.5 Mhz and 31.5Mhz.. How is this even possible? is it possible that my friend misread the meter?

 

[Marconi]

Mr_Fx, that 1/4 wave should show a large bandwidth, but that is more than I see with my 1/4's. I can get maybe 3-4 megs sometimes, but that is about all I ever seen.

If your feed line is old, I would check it to see if it makes the watts through it you expect. If the line is new, you're probably OK, but I check all of my lines every time I take them out of service and I record the results.

I would put a meter and a good dummy load at the far end, and see if you're getting all the watts through it you should.

If your line is RG8 or better, and about 100 feet or so...you should see at least 90% of what your radio will produce when you check the radio output hooked close to the dummy load using your radio.

Check your radio's output.

Radio---meter---dummy load

Check your lines thru put.

Radio---------------------------------------------------meter---dummy load

Here is an old list I found in my notebook.



Good luck and keep us posted.

 

[AudioShockwav]

If your feed line is old, I would check it to see if it makes the watts through it you expect

I second that.
When I first got my I-10K from Jay, I plotted the SWR curve, and it was very wide, ( I was running some rather old rg8x if I remember right) so much so that I even called Jay and talked to him about this.
His thoughts were the same as Marconi`s and he said he had seen this before with old coax.
At some point later, I pulled the antennas down, and changed to some good quality ( belden) coax, and the SWR fell in line just as Jay said it would.

73
Jeff

 

[Captain Kilowatt]

It could also be high ground losses. That will cause an apparent W I D E bandwidth as well.

 

[Beetle]

Taken to extremes, you're discovering how dummy loads get such wide bandwidths...

 

[Marconi]

I second that.
When I first got my I-10K from Jay, I plotted the SWR curve, and it was very wide, ( I was running some rather old rg8x if I remember right) so much so that I even called Jay and talked to him about this.
His thoughts were the same as Marconi`s and he said he had seen this before with old coax.
At some point later, I pulled the antennas down, and changed to some good quality ( belden) coax, and the SWR fell in line just as Jay said it would.

73
Jeff

Jeff, I've told this story before...about how I discovered my coax had deteriorated due to water in the line over some extended period of time. The effects I noticed were profound to me. Not only did I notice a very wide bandwidth indication on the Starduster at the time, I had an extremely quiet receive, that I realized locally.

Often I was able to fully copy contacts that my neighbors could only hear as noise. I claimed that was my Starduster doing that. At the time the guys all around and close by all complained of static noise, and I had no static or noise.

The really big think I realized after I fixed the problem, by changing the coax, was that my transmit was also diminished in a major way...that for the better part of a year operating with this 100' RG8x clear coat coax. During that time I never had a clue, and not one person ever told me, locally or DX, that my signal was way low compared to a buddy just 3 blocks away.

When I tested this coax with 25 watts imput...I got only 3 watts at the far end. This is when I started testing the thru-put for all of my feed lines on a regular bases. This is also when I realized a lot of the stories I was hearing about the real need for power was probably somewhat of an unnecessary expectation.

The gist of these ideas of mine are base on speculation and experiences. Although I was only getting about 10% percent of my power out into the air...I thought in a perfect world without ground clutter and noise, maybe this was all the power I really had to have to communicate locally and in DX.

The other great and profound benefit was my receive really seemed great too. I was sorry that I cut that feed line before I used it to test further the ideas above.

BTW several antennas like the A99/Imax, Starduster, Maco V58 also have a feed point setup that allows water to get directly into the feed line, and caution is suggested.

 

[mr_fx]

I forgot to mention that the radials are made out of 18 gauge galvanized electric fence wire

I think it is ground losses, maybe just losses in general

not a coax issues, the readings where taken with 1.5 feet of RG8x

 

[mr_fx]

almost identical to what I built, but I go EMT for the radiator and, and I have galvanized electric fence wire for the radials (and 4 instead of 3) looks like nearly the same wide bandwidth too

http://www.worldwidedx.com/cb-antennas/35651-cheap-easy-ground-plane.html