Measuring antenna length

I asked the fellow novice ham in my neighbourhood what length his silver rod was. I got the answer 5.145 m accompanied with a series of pictures of which the pic showed is one. He measures the length from the "plastic" support on top of the mount to the end of the antenna. I measure from the bottom of the mount, where the wire connects to the radiator. I think he is more correct as for the length of the mounting clamp there's a combination of radiator and "ground". The pure radiator part starts where he starts to measure (in my opinion, in fact on top of the clamp, on the bottom of the "plastic" support). Never thought about it this way....


73

Karel

It's something that has crossed my mind in the past, but never really given it any proper though till you asked the question. I am going to theorise that you are the one who measured correctly.. measure from the very bottom where the wire connects to the radiator.

My reason to say this is that even though this is an end fed half wave, a half wave is a half wave and so it's current maximum, and where it radiates the most from, is the centre of he antenna. The very ends are less important. The ends can be bent about, or even covered by a bit of "ground" as in this case, and will have very little effect on its performance.

Just my opinion, don't take my answer as de facto  Would be interested to know other peoples thoughts on it.

Likely the entire antenna will radiate so measure from the SO239 rivets. Even though it has a DC short the bit of rod in the bracket is likely to radiate.

Do remember that any current centre will only be in the middle of the antenna for 27/28MHz. It will be moving with frequency.

Using this rod will change the current centre along with frequency as the antenna becomes more or less like 1/2, 1/4 or even 1/8 wave.

For example 1/4 wave current centre is at feed point (on 20m band 5m of rod is similar to 1/4 wave at that frequency).

I also like to model my antennas in CocoaNEC or 4NEC2, so i'm curious which length i should put in the model. I'm not that good in modelling to put a piece of ground and a piece of radiator on the same height.

karelgol wrote:

I asked the fellow novice ham in my neighbourhood what length his silver rod was. I got the answer 5.145 m accompanied with a series of pictures of which the pic showed is one. He measures the length from the "plastic" support on top of the mount to the end of the antenna. I measure from the bottom of the mount, where the wire connects to the radiator. I think he is more correct as for the length of the mounting clamp there's a combination of radiator and "ground". The pure radiator part starts where he starts to measure (in my opinion, in fact on top of the clamp, on the bottom of the "plastic" support). Never thought about it this way....


73

Karel

Why are you measuring it please?

"Why are you measuring it please?".

I had some trouble getting this antenna to work, so i asked a fellow ham, who also uses a silver rod as multiband HF antenna, to measure his antenna. Adjusted mine to this length and still not working. Then i dismantled the whole system and measured every part for continuity (except the UNUN). It turned out the new hyperflex 5 cable i bought (ready made with the special PL259 plug) had a short between shield and wire. Remounted both plugs and finally solved my antenna issues. So my advice to everyone would be "when buying ready made parts, test, test and test again before use".

73
Karel

Well said there Karel.  

I have purchased a few 'pre-terminated' cables in the past and quite often they are appallingly put together with either whiskers of copper braid floating around inside connectors or poorly soldered centre connectors. An immediate short or open circuit can be easily found but such shoddy workmanship usually rears it's ugly head after you've connected it up to your equipment!

Hence why I now make all of my own cables.....then I can only blame myself if it all goes wrong.

Nice tip there Karel and good luck with the antenna.

73
Victor

karelgol wrote:

"Why are you measuring it please?".

I had some trouble getting this antenna to work, so i asked a fellow ham, who also uses a silver rod as multiband HF antenna, to measure his antenna. Adjusted mine to this length and still not working. Then i dismantled the whole system and measured every part for continuity (except the UNUN). It turned out the new hyperflex 5 cable i bought (ready made with the special PL259 plug) had a short between shield and wire. Remounted both plugs and finally solved my antenna issues. So my advice to everyone would be "when buying ready made parts, test, test and test again before use".

73
Karel

Ah ok , i have a cheap silverrod half wave from moonraker it has no marking's for the correct length on cb band , it was alot of messing about tbh to get the swr correct.  i think it ended up about 5 metres .

I puchased  the Silver rod 5/8wave  handfull of years ago.  I guess I may have cheated using  a vertical antenna caculator  to do a quick set up.  The analyzer read I was close, Tinkered a little this way or that way and was dialed in , in no time really. I never thought to measure the length afte done.  I did remove the 3 little radials , I added 8 )  9ft radials  with 2 Maco Ground radials hubs. We had the radio shack Crossbow64  .64 wave ground plain in the late 1970's into the 1980's  I was going for a close replica in 5/8wave form. ( crossbow 64 had 4 ) 9ft radials not 8, I figured I had the pieces, why not? tuned very well and widend the coverage a little. Nice quiet RX as well. 2CT351

For me the choice for the silver rod was, because a lack of space in my garden, so also not much room for radials. But what would you recommend? Using the 3 small 1' radials, or just omit them?