Maco V58 - My first station antenna - Feedline Question

[Rok55]

Just getting into the hobby with purchase of a Uniden 880 for mobile and a Uniden 980SSB for the base. Purchased the Maco on recommendation of longtime friend and Ham. I have the Maco assembled and ready for test n tune at approx 8' above earth at a location approx 25' from the house and will be raised to approx 20' after tuning. Station will be on second floor on same side of house.

I have a 100' of RG8X with PL259 on each end that will eventually be cut to proper length when antenna is raised and my connectors arrive.

#1 How do I (or can I) tune the Maco with what I have on hand or do I need to have the correct length of feedline available prior to testing?

#2 How do I figure the correct total length of feedline required to run this antenna on the CB band?

Thanks in advance ..........

Rocky

 

[wavrider]

https://www.rightchannelradios.com/blogs/installation-guides/18428275-understanding-swr

http://www.wearecb.com/how-to-tune-cb-antenna.html

If you have the proper equipment then you should be able to tune the antenna .

Follow manufactures instructions on how to tune the groundplane.

Coax length is whatever is needed to reach the operating station plus a few feet more.

 

[dave457]

Yes, there is no correct length!
Just use what ever it takes to get from point A to point B,
I would just use that 100' of coax, always better to have more than not enough

 

[M0GVZ]

1) No such thing as a required length other than that needed to get from radio to antenna. The reason the old 9ft/18ft/27ft bollocks got traction is that people who did piss poor installs of antennas with piss poor RF grounding found that if they used those lengths they got low SWR. What they didn't know is the reason they did was because the coax was forming part of the antenna due to the poor RF ground.

So.....

Use the length of coax needed to get from rig to antenna and don't bother measuring it. RF choke at the antenna feedpoint which can be done by making 5 turns of 4.25" diameter out of the coax, don't tie the coax to the mast the antenna is going onto or you defeat the object of the choke and tune for low SWR slightly lower by maybe 5-10 channels than the frequency you want it on as the antenna tuning will alter as you raise it higher above ground. Use self amalgamating tape or coax seal on the PL259 at the antenna end to prevent water getting in. Coax is especially good at wicking up water. Also as long as the SWR is below 1.6-1.7:1 on all the channels you use, be happy at that. There is no advantage to going lower.

 

[Rok55]

Thanks for the input folks and for the links. I am familiar with SWR meaning and need for proper tuning and do own an SWR meter. Have been doing a bit of reading on the subject matter and have found contradicting info on coax length requirement, hence the question for clarity from the group.

As the Maco is at a height I can work with, my thought was to initially insert the meter at the antenna location, tune the antenna, ands then move the meter to the station end to verify coax integrity. Should I bother doing it this way or just do all testing from the station.

The 100' of coax will be significantly too long during testing, I assume I should lay the excess out to eliminate any coils along the way?

RF choke at the antenna feedpoint which can be done by making 5 turns of 4.25" diameter out of the coax, don't tie the coax to the mast the antenna is going onto or you defeat the object of the choke....

In terms of the choke I assume you means something like this :

I have read that an additional choke prior to entry to the shack should also be considered. Yes ......... No ?

I thought it appropriate to secure the coax (zip ties or tape) to the mast to relieve strain on the connectors and limit excess movement of the coax. How and where do I secure the coax as I make the trip down to earth and then back up the wall to the shack?

 

[Mustang 131]

Thanks for the input folks and for the links. I am familiar with SWR meaning and need for proper tuning and do own an SWR meter. Have been doing a bit of reading on the subject matter and have found contradicting info on coax length requirement, hence the question for clarity from the group.

As the Maco is at a height I can work with, my thought was to initially insert the meter at the antenna location, tune the antenna, ands then move the meter to the station end to verify coax integrity. Should I bother doing it this way or just do all testing from the station.

The 100' of coax will be significantly too long during testing, I assume I should lay the excess out to eliminate any coils along the way?



In terms of the choke I assume you means something like this :

I have read that an additional choke prior to entry to the shack should also be considered. Yes ......... No ?

I thought it appropriate to secure the coax (zip ties or tape) to the mast to relieve strain on the connectors and limit excess movement of the coax. How and where do I secure the coax as I make the trip down to earth and then back up the wall to the shack?

Always start the tune at the antenna, chance are your swr will be low if you measured correctly and your at least 8' from the ground.
If your using an antenna analyzer, keep it and yourself at least 10' away to avoid throwing the tune off. (Note: Many people smarter then me have and will disagree, but it works for me.)
I then tune the antenna for the lowest swrs at the end of the coax. If done correctly the swr will not be much different, and the lower swr at the radio will keep your finals happy.

Use a PVC pipe or a used elecrical spool, 5 raps for the rf choke.

 

[Rok55]

Thx for the response.
I will be using an Astatic SWR meter and was curious about my presence affecting the SWR while observing the meter. I was planning to have SO key the mic as I adjusted set point and observed the reflected reading, your response tells me that isn't the best plan. So I suppose I need a jumper that will put me at least 10' from the base of the antenna, or do I need to be completely away from the radials?

 

[M0GVZ]

In terms of the choke I assume you means something like this :

I have read that an additional choke prior to entry to the shack should also be considered. Yes ......... No ?

I thought it appropriate to secure the coax (zip ties or tape) to the mast to relieve strain on the connectors and limit excess movement of the coax. How and where do I secure the coax as I make the trip down to earth and then back up the wall to the shack?

Yes a choke like that, 5 turns on 4.25" former, and no harm having another one. If you are using a metal mast the reason you don't secure the coax to the mast on the shack side of the choke is the mast will be hot with RF as it forms part of the RF ground so that would end up back on the outside of the braid which was what you were using the RF choke to prevent in the first place.

It doesn't need to be far away from the mast so you could make some small spacers even just an inch wide out of some blocks of wood or plastic and place them between the mast and the coax where you would normally intend to cable tie or tape the coax to the mast as it came down from the antenna.

You don't want to be touching the antenna when someone is transmitting because you can get RF burns. Best to have them key up the mic, shout out the reading, de-key, you make a slight adjustment, rinse and repeat. Buying or borrowing an antenna analyser saves you all of this grief, making them worth their weight in gold especially when you initially build an antenna and it ends up being resonant outside of the range of frequencies your CB covers. Then it saves you a whole lot of stabbing in the dark.

 

[M0GVZ]

If your using an antenna analyzer, keep it and yourself at least 10' away to avoid throwing the tune off.

As long as you're below the feedpoint and the radials you'll be OK. Shorter the length of coax from antenna to analyser the more accurate the readings.

 

[Rok55]

M0GVZ .......... thanks much for the comeback and clarity, truly appreciated.

Don't have access to an analyzer other than my SWR meter so will have to muddle along with that.

I'll be running a commercial grade copper line (from electric service transmission / distribution poles) (believe it is approx. 3/8" dia) for grounds from the mast to my earth grounds as well as from the shack to earth grounds, should I setup a ground buss bar in the shack as well for chassis grounds, are there any other precautions I should take?

 

[M0GVZ]

I've never felt the need for one because if you're doing it for RF grounding then that should be taken care of long before the coax gets to the radio. For electrical safety we don't need them in the UK but I'm not sure what code requirements you may have on that side of the pond.