Sidebar Sidebar
  • You can now help support WorldwideDX when you shop on Amazon at no additional cost to you! Simply follow this Shop on Amazon link first and a portion of any purchase is sent to WorldwideDX to help with site costs.

A99 VS. I MAX CHOICE AT IMPROPER HIGHT

I'm trying to decipher what you are saying. So the swr is good , dead flat at about ch 20 but your meter is showing lower power out. Is that correct?
You have cut out 30 ft of coax i would expect to see a difference on the SWR.
The load has changed at the tx end.I suspect is you use an ant analyzer you will see a highly reactive load.
 
I had my imax 2000 on an 8 foot Comer post minus 3 of those feet in ground, and attached it as high up on the post, it was half way above the roof, about 20 feet down behind the house and did not clear the top of the power lines in front of the house 50 feet from the antenna. Worked great for me, but to tell whole deal I was 1060 plus feet above sea level to on a Ridge lol...
Wonder what it would of done had it been on a 36' or 50 foot push pole?
 
vkrules said:
You have cut out 30 ft of coax i would expect to see a difference on the SWR.
Click to expand...

If the antenna is installed properly you should see no difference. If you do its because you've got common mode and the coax is forming part of the antenna which you do not want both because you get RF in the shack as well as interference to other devices when you TX and additional noise when you RX.

Whether you use 2ft of coax, 20ft or 200ft or anything inbetween you should see the same SWR with a properly installed antenna.
 
What about people who say 492 x velocity / freq for lengths of coax, minus 6', 9', and 12' jumpers. How accurate is that, especially for a wide banded antenna such as the imax 2000 or even a multi banded fan dipole vs a single mono bander?
 
Last edited:
M0GVZ said:
If the antenna is installed properly you should see no difference. If you do its because you've got common mode and the coax is forming part of the antenna which you do not want both because you get RF in the shack as well as interference to other devices when you TX and additional noise when you RX.

Whether you use 2ft of coax, 20ft or 200ft or anything inbetween you should see the same SWR with a properly installed antenna.
Click to expand...
I agree with most of what you have to say and we both agree his load is reactive. But unless the load is a 50 ohm resister I would expect to see a slightly higher swr with a reduced bandwidth due to the return loss of the 30 ft of cable at 11 meters.
But come on, inexperienced operator ,a99 mounted 15 ft of the ground ,objects in it's near field , no choke ( at last report), swr tested at end of cable. Then raised another 5 ft, 30ft of cable removed. And driven with 1kw pep.
What could possibly change !!!
 
Heavy Metal said:
What about people who say 492 x velocity / freq for lengths of coax, minus 6', 9', and 12' jumpers. How accurate is that, especially for a wide banded antenna such as the imax 2000 or even a multi banded fan dipole vs a single mono bander?
Click to expand...
If the antenna is resonate and perfectly matched then there is no need as MOGVZ said.And no doesn't work for multband antennas.
 
vkrules said:
If the antenna is resonate and perfectly matched then there is no need as MOGVZ said.And no doesn't work for multband antennas.
Click to expand...



What does work for multi and antennas and far as length of and length of jumpers or jumpers rule of.thumb still apply no matter what between 6' to 12' aka 6 9 12?
 
Heavy Metal said:
What does work for multi and antennas and far as length of and length of jumpers or jumpers rule of.thumb still apply no matter what between 6' to 12' aka 6 9 12?
Click to expand...


What works for multiband antennas? Tuning each band to resonance and using enough coax cable to reach the gear in the shack is what works 100% of the time. No special or magic lengths of cable required or desired. Asd for interconnecting jumpers the proper length is determined by the use of a measuring tape. Measure how far from point A to point B and insert the closest length or cable that reaches.
 
  • Like
Reactions: 222DBFL and wavrider
So, Capt K, all the bs is bs, no, magic lengths ect...

No.effect either on swr if antenna is resonating right.
 
Yep, a lot of BS!!! I have installed thousands of coax jumpers from commercial RBS (Radio Base Station), equipment, mainly for Ericsson and ATT/Cingular, and the only time length of coax was an issue was with length due to losses, not any magic numbers from equipment to hatch plate. Have installed Andrew, Commscope, Eupen, RFS, and a bunch of others as well, ranging from 1/2" super flex to 1 5/8" hardline, and prett well everything in between. From the equipment to the hatch plate all coax was hand cut and Din male connectors either straights or 90's depending on the equipment would be terminated at both ends then swept with and anristu and then PIM tested after that. If you need to use a certain or specific length of coax is if the manufacture stated it or it was a specialized piece of equipment. Just my 2 penny's.
 
Heavy Metal said:
What does work for multi and antennas and far as length of and length of jumpers or jumpers rule of.thumb still apply no matter what between 6' to 12' aka 6 9 12?
Click to expand...

My Hexbeam covers 14, 18, 21, 24, 28 and 50MHz. What length do I choose? When I ran my 75ft long inverted L I ran that with a SGC230 antenna coupler on 1.6, 3.5, 5, 7, 10, 14, 18, 21, 24 and 28MHz. What length do I choose for that?

Shortest length between transmitter and antenna and between all accessories (rig to SWR meter etc) is the only correct answer for both and its the same for CB. If the length of coax is critical to getting a good SWR then that has to be because the coax is forming part of the antenna which we do not want. And unless the antenna is a design that is meant to do that then the only reason it is is because the antenna system hasn't been installed properly, usually down to a piss poor RF ground and lack of choking.
 
  • Like
Reactions: The DB
222DBFL said:
If you need to use a certain or specific length of coax is if the manufacture stated it or it was a specialized piece of equipment. Just my 2 penny's.
Click to expand...

Indeed. The only time I've come across lengths of coax being critical is in a VHF/UHF repeater system where you have to use 1/4 wave and 1/2 wave length patch leads between the various cavity filters and isolators etc and with the harnesses on stacked folded dipoles because of the way it all works with phasing. On HF the only time I've come across where its critical is when you're using phasing such as in a steerable four square array.
 
  • Like
Reactions: 222DBFL
The only reason i cut the 30' off was when i ordered the cable (LMR 400) i purchased 130' because I had not decided where the a99 was going to be installed as far as the distance from the radio to the antennas feed point (so239).
The a99 was installed where only 95' was needed and 35' was Just laying around the yard.

I left an extra 5' on so i could move the station though out the room if need be.
The added 5' mast did nothing but cause problems.

It was just my bad luck that before I could take and write down my readings on 1,20 and channel 40 then post the readings for advice on what to do to optimize my antennas performance,
I lost out put on AM shortly after taking some readings on channel 1and couldn't continue (coincidence I hope usb and lsb were not affected).

The problem was a bad mixer ic. I had it repaired and just received it back. I will be hooking the Madison back up in a day or two but cant use it until i receive the meter and dummy load.
Unfourtunatly I will have to add the 30' back via a barrel connector. I decided (foolishly) not to add the choke because of the conflicting
amount of turns and diameter.for LMR 400 I was getting.
I now know it's five turns at an 8" diamater installed two feet below the feed point.

I'm fairly positive I need the Choke but won't know for sure untill I post my readings and y'all can advise me.

I purchased the dummy load after returning the mfj 826b. I found it impossible to tune my amp with the 826b as the digital functions of the power readings were not for me.
I swapped it in for the 828 which has the cross needle meter and the digital features of the 826b.
I made what was a minor problem a major one and learned a lesson. .If it's not broken dont fix it. I don't know how the extra 5' mast caused a minor problem to become a much larger or if that's even what made a decant station that made daily contacts with no problem what so ever stop doing that but because of my mistake I began to read about how to take meter readings with the dummy load and then the antenna. Writing down these readings and comparing them. This may leed to a solution.

If need be I will take down the whole antenna and start from scratch.
I was basically gonna give up and pack everything away but I think it was waverider who inspired me by saying something to the affect that no matter what the problem, There's always a fix.

The issue causing all the problems from the beginning is I cannot put the antenna on my or above my roof line, period.
I'm going to have to get my antenna to work the best it can with the hight and the site it sits at in my yard.
As soon as I recive the dummy load and meter (Saturday).
I will post all dummy load readings stock then with the amp inline.
Then all readings stock then with the amp inline while hooked up to the antenna.
I will wait to hear from all who will give advice and without rushing take it step by step to see if I can get the antenna readings to aacceptable operating conditions so I can begin enjoying dx'ing again. Thanks. QUOTE="vkrules, post: 525682, member: 24352"]I'm trying to decipher what you are saying. So the swr is good , dead flat at about ch 20 but your meter is showing lower power out. Is that correct?
You have cut out 30 ft of coax i would expect to see a difference on the SWR.
The load has changed at the tx end.I suspect is you use an ant analyzer you will see a highly reactive load.[/QUOTE]
 
Last edited:

dxChat
Help Users
  • No one is chatting at the moment.


      Top Bottom
      Back