Homemade antenna Issue High SWR

[Gunner357]

Beats me. At 1.7 try communicating with it.

I tried last night, I wasn't getting out OR everyone had lock jaw

 

[Gunner357]

first thing I would do is put a dummyload at the end of the rg213 & make sure everything is as it should be, & a good match with no cmc on the braid actually gives you a near flat vswr at the analyzer/meter,

a copper tube dipole should tune no problem,
its fat so needs to be a little shorter than a bare wire,
its inside a plastic tube that adds dielectric loading & slows the vf a little so it need to be a little shorter than if it was in air,

you can't make proper measurements ( of the antenna feed-point ) without putting an effective choke just below the copper tube to isolate as best you can the coax braid been part of the antenna,

no choke causes vswr & pattern to change with coax length & position,

measuring your dipole through a random length coax won't tell you what's going on at the feed-point even if you have the best choke in the world & zero cmc on the braid

if you want to know about the antennas impedance & where its resonant your coax must be cut so its a multiple of electrical 1/2waves from the feed-point to your meter/analyzer on the frequency you want it tuned for,

anything other than electrical 1/2wave or multiple 1/2waves will transform the impedance seen looking into the analyzer end of coax and move the resonance point.

The user manual for your analyzer should explain why you can't use random length
coax for impedance & resonance measurements,

my buddy recently made the same antenna by converting a fat sirio 827 5/8wave groundplane into an aluminum 1/2wave dipole with no problem getting it tuned & working as well as any 1/2wave at the same height.

Ive tested the coax already with the Analyzer and a VOM, Im using the same coax(RG213) lead that is going to be used when it installed in the house ( Aprox 60ft meter says 62.3ft) Now there a 3-4ft pigtail coming out from antenna (RG8X mini) Ive tried hooking to that and got stupid high SWR 10-12.0 never seen anything that high before So I thought a short, so I took it apart and saw no where that can be shorting out. As soon as I put the 60ft of RG213 on SWR dropped to 7.0 then I started tuning from there In the middle of my yard using a Deck umbrella cast iron stand and a 5 ft piece of steel mast, I did not have a choke on it at this time. So I don't know what else there is to do OBVIOUSLY I'm doing something wrong ...Ive installed many antenna's never Homemade ones ....

 

[Gunner357]

I usually build them to general specs then mount them at 21' feedpoint and tune them there. Then I raise them higher, usually to 34'. I work from this platform.View attachment 39601

When I can not work from there on the platform I set a fiberglass step ladder in the yard with a 10' EMT pipe sticking up through it. Antenna is mounted on a smaller EMT pipe inside that one. I tune, then push the inner EMT tube up to get the antenna feedpoint to 19' height to take SWR sweeps.

Whoa too high for me your a brave man work off that platform LOL

 

[Gunner357]

I just put a dummy load on the coax and used analyzer and across 27mhz 1.06 SWR just making sure

 

[bob85]

do you have a pic of the tuning setup tripod metal mast ?,

if you don't put a choke just under the tube the lower part of your antenna is a copper tube 1/4wave long in PARALLEL with the coax braid,
which is 3ft of rg8x + 62ft of rg213 + whatever else is inline with your equipment back to ground,

the last thing you want is the coax acting as part of the antenna radiating & picking up local noise sources

you want the tube to be carrying most of the current with as little as possible on the coax braid,
a correctly made choke under the tube helps in almost all cases.

if the choke isolates the braid well the vswr you measure will be close to the actual match of the antenna to your coax,

if it does not isolate well & you have current on the braid you are not measuring the antennas match to the coax ,

you are measuring the match of the load seen at the far end of the coax which is the antenna plus the outside of the coax braid,

if you isolate the coax braid well vswr will not change significantly with coax length, but resonace and impedance will still move around with different coax lengths,

unless you have a good 50ohm dummyload in place of the antenna so there is a perfect match & no current on the braid,

if you want to measure the antenna impedance or determine if its resonant on your chosen frequency,

cut the coax to be electrical 1/2wave multiples at that frequency,
isolate it from the antenna best you can, sometimes a second choke lower down can help too,

then you can measure the feed-point impedance and resonace of the antenna and its match to the coax from the analyser end of the coax on your frequency of choice.

 

[Gunner357]

do you have a pic of the tuning setup tripod metal mast ?,

if you don't put a choke just under the tube the lower part of your antenna is a copper tube 1/4wave long in PARALLEL with the coax braid,
which is 3ft of rg8x + 62ft of rg213 + whatever else is inline with your equipment back to ground,

the last thing you want is the coax acting as part of the antenna radiating & picking up local noise sources

you want the tube to be carrying most of the current with as little as possible on the coax braid,
a correctly made choke under the tube helps in almost all cases.

if the choke isolates the braid well the vswr you measure will be close to the actual match of the antenna to your coax,

if it does not isolate well & you have current on the braid you are not measuring the antennas match to the coax ,

you are measuring the match of the load seen at the far end of the coax which is the antenna plus the outside of the coax braid,

if you isolate the coax braid well vswr will not change significantly with coax length, but resonace and impedance will still move around with different coax lengths,

unless you have a good 50ohm dummyload in place of the antenna so there is a perfect match & no current on the braid,

if you want to measure the antenna impedance or determine if its resonant on your chosen frequency,

cut the coax to be electrical 1/2wave multiples at that frequency,
isolate it from the antenna best you can, sometimes a second choke lower down can help too,

then you can measure the feed-point impedance and resonace of the antenna and its match to the coax from the analyser end of the coax on your frequency of choice.

all the Pics are posted above step by step on how I made the connections and my test mast etc. Well most of the build....... forget first few pic thats the first dipole problem... I did make up a choke this am and the SWR jumped to 12 13 14 so I went and baught an antenna BUT Im still going to get this thing right if it kills me I bought more coax too so I can re do the the antenna with RG213

 

[bob85]

i don't see anything obvious with how you built the dipole,

i don't see the choke as close as you can get it to the bottom copper tube,

trying to tune a sleeve dipole on that temporary metal stand so close to ground with coax on the ground is no good,
you need it up where it will be used or a similar height above ground to tune it, inconvenient but that's radio,

if winding a 5 turn x 4.25" former choke in your coax causes vswr to jump to the numbers you claim you have a serious problem,
common mode or the antenna been off by a few inch won't cause vswr anywhere near that high,

redoing it with 213 all the way with no joints is a step in the right direction.

good luck.

 

[S&W357]

Hook up that store bought antenna and give it a try. Lots of DX coming into NC from Michigan today.

 

[BJ radionut]

Gunner: Boy you have had FUN!!!
Wonder what antenna you purchased?
Now as to getting this present project to work, here's a thought.
Once you get the other antenna an it's tuned and ready, why not reconfigure(rebuild) this antenna Horizontal below the other? Building for Horizontal usage certainly solves many issues with coax and mounting!!!
I think you will find having the 2 different polarities will be an advantage when the conditions go long. (band openings)
Set the Horizontal dipole so the "ends" point NNW and SSE would be good direction in Northern Mich.
That would put the broadside(strongest signal strength) to most of the South Western part of the US, as well as Upper NE Coast, part of Eastern Canada and looking toward most of Europe
Something to think about!!!
All the Best
Gary

 

[S&W357]

Go for it Gunner. BJ’s idea is a good one.

 

[Gunner357]

Hook up that store bought antenna and give it a try. Lots of DX coming into NC from Michigan today.

Its on a temp stand trying to match go figure this is being a pain 2.0 ch 1 1.4 ch20 1.3 ch 40 on My Dosey If i hook up the Analyzer its higher on 1 2.4
lmao

 

[Gunner357]

Gunner: Boy you have had FUN!!!
Wonder what antenna you purchased?
Now as to getting this present project to work, here's a thought.
Once you get the other antenna an it's tuned and ready, why not reconfigure(rebuild) this antenna Horizontal below the other? Building for Horizontal usage certainly solves many issues with coax and mounting!!!
I think you will find having the 2 different polarities will be an advantage when the conditions go long. (band openings)
Set the Horizontal dipole so the "ends" point NNW and SSE would be good direction in Northern Mich.
That would put the broadside(strongest signal strength) to most of the South Western part of the US, as well as Upper NE Coast, part of Eastern Canada and looking toward most of Europe
Something to think about!!!
All the Best
Gary

My plans are shit canning the mini 8 ,,,I got 20ft RG 213 Im going to re do all of it I got a V58 Maco wanted a Hy Gain but to impatient my place here in Mi and hour away had a good price on them

 

[Gunner357]

Thank You ALL for your help....

 

[HomerBB]

Gunner, have you gotten your V58 tuned?

 

[Marconi]

Homer, do you think that V58 might give Gunner some problems tuning too? I've got my fingers crossed.