Through Wall Antenna Connection ??

[Eltee]

I am looking for the device that is threaded to connect antenna cable from one side of the wall to the other so I can get my base antenna outside. I don't know what it's called but I thought it looked like a threaded rod that only needed a small hole through the wall. You connected a standard antenna cable on either end, one to the radio and the other to the antenna. Don't know what it is called, where to find it, or if it works well.

Thanks for any info.

Newbie 

[axorlov]

Bulkhead antenna connector. But they are usually not that long. Not long enough to reach through your normal 2x4 frame + drywall + siding + etc. Also PL259 bulkhead connector will need a hole bigger than LMR-400 cable would need.

[wayoverthere]

I searched "so239 through wall" and that found lots of options in varying lengths.

Here's one listing: https://www.amazon.com/Female-Bulkhead-Coaxial-Connector-Connectors/dp/B075TK89VZ

[WyoJoe]

14 minutes ago, wayoverthere said:

I searched "so239 through wall" and that found lots of options in varying lengths.

Here's one listing: https://www.amazon.com/Female-Bulkhead-Coaxial-Connector-Connectors/dp/B075TK89VZ

That looks like an interesting way to get through the wall, but it may not work well for GMRS. As I read the reviews, one stood out to me.

Here is what Ryan G said about the SO-239 bulkhead connectors:

Quote

Ryan G.

4.0 out of 5 stars Works great for 2m band and below. NOT for 70cm band.

Reviewed in the United States on December 6, 2018

Verified Purchase

First of all, if you are going through an exterior house wall, you probably have 6" studs. By the time you add drywall, siding, cover-plates and nuts, an 8" bulkhead isn't long enough to give you enough threads to connect to...you'll need 9 inches...which means you need to use a 10 incher.

I have tried both an 8" and a 10" bulkhead from different sellers and both had excessive SWR in the 70cm band. I think the problem is that they are air core and not controlled impedance, combined with the length being between 1/4 and 1/2 wavelength at 70cm. The conductor most likely develops a standing wave within the bulkhead and the impedance begins to deviate wildly, causing reflections and high SWR. With the 10" bulkhead I got nearly 1:1 SWR at a very specific frequency (I think 445MHz) and skyrockets to >5:1 rapidly as you move away from that frequency.

I am now going to try just using a simple flanged (panel mount) bulkhead (ASIN: B00CX01IYM) on the exterior wall and running my 6' interior feedline through a pass-through wall-plate (ASIN: B00DL93SLU) on the interior wall. I may end up putting a second bulkhead on the interior wall plate and using a 12" coax jumper (ASIN: B00KYYU1YW) to connect the two bulkheads inside the wall.

 

This may have been an anomaly, as it was the only review that indicated a high SWR, but it's at least worth considering if you go this route.

 

[wayoverthere]

4 hours ago, WyoJoe said:

This may have been an anomaly, as it was the only review that indicated a high SWR, but it's at least worth considering if you go this route.

 

Yeah, if I were going this route, Amazon isn't super likely to be my first choice. I was intending it more as illustrative than a specific recommendation.

In my case, my office/shack contains the access panel for the crawl space, so I'll likely just use that and one of the foundation vents to get my coax outside, or a bulkhead in the floor in the closet next to the panel

[gortex2]

You'd be better off just running the cable thru the wall and sealing it up. You will have loss in the connectors and bulkhead connector. 

[plarkinjr]

On 10/31/2021 at 6:22 AM, kb2ztx said:

You'd be better off just running the cable thru the wall and sealing it up. You will have loss in the connectors and bulkhead connector. 

At what point would you connect a lightning arrestor and ground?

[JimSmitty]

34 minutes ago, plarkinjr said:

At what point would you connect a lightning arrestor and ground?

At the point the cable enters the house is what I have read, and will be doing at my home. With a lighting arrestor, to a 10 guage ground wire, to an 8ft ground rod. A 1 or 2db loss is worth the protection. 

[mbrun]

At what point would you connect a lightning arrestor and ground?

Immediately before the feed-line enters the house. You should locate the ground rod in close proximity and connected to the arrestor. Further, you should interconnect your new ground rod to your existing electrical service entrance ground rod directly by way of a bonding conductor (e.g. #6 bare copper). This bonding conductor is expressly covered in the National Electric Code. It serves to further minimize voltage potential between the shield of the feed-line and the electrical grounding conductors in your home.


Michael
WRHS965
KE8PLM

[Lscott]

19 hours ago, mbrun said:

Immediately before the feed-line enters the house. You should locate the ground rod in close proximity and connected to the arrestor. Further, you should interconnect your new ground rod to your existing electrical service entrance ground rod directly by way of a bonding conductor (e.g. #6 bare copper). This bonding conductor is expressly covered in the National Electric Code. It serves to further minimize voltage potential between the shield of the feed-line and the electrical grounding conductors in your home.


Michael
WRHS965
KE8PLM

I believe some antennas have a DC connection from the radiating element to the shield. Grounding the shield bleeds off static electricity buildup and generates less noise in the signal while protecting the sensitive front end components from failure. You can get huge static voltage build ups even on sunny days just due to a small breeze blowing across the antenna.

I read a story about one Ham who got knocked off his roof after touching his un-grounded antenna, no feed line attached, due to the static voltage on it.

I also know people who will disconnect the coax from all their radios, sticking the ends in glass jars, when thunder storms are moving in to the area.

[mbrun]

I believe some antennas have a DC connection from the radiating element to the shield. Grounding the shield bleeds off static electricity buildup and generates less noise in the signal while protecting the sensitive front end components from failure. You can get huge static voltage build ups even on sunny days just due to a small breeze blowing across the antenna.
I read a story about one Ham who got knocked off his roof after touching his un-grounded antenna, no feed line attached, due to the static voltage on it.
I also know people who will disconnect the coax from all their radios, sticking the ends in glass jars, when thunder storms are moving in to the area.

Whole heartedly agree on the static build up. Proper grounding helps to bleed off static caused by wind and as well as the spikes caused by environmental electrical disturbances nearby. While grounding will not save you in the event of a direct hit, if done correctly, it will save you from injury and property damage from more likely and frequent causes of shock, equipment damage and some noise. Bonding is a key step in the grounding process that too many people ignore because they don’t understand its purpose.


Michael
WRHS965
KE8PLM

[SUPERG900]

Hmm - just ran across this thread.

I wouldn't say that bulkhead connectors won't work with 70cm..... especially considering that the majority of mobile amateur radios doing UHF and used in the home are dual UHF/VHF with an internal diplexer and a SO-239 antenna connector....  If using a bulkhead has any major effect on vswr at all, it's either defective or there's something funny going on in your wall...

I'm basically using two 6" so-239 bulkhead connectors attached to two stainless steel outlet covers as a through-the-wall bulkhead. You can buy these covers at any hardware store.

One connection is is for a dual-band VHF/UHF antenna, and the other is for an HF antenna.  Properly made these bulkhead should be grounded at exterior of the house to a grounding rod. Also, lightening surge suppressors should be installed for the coax and grounded to the rods as well.

This is a VSWR scan of a Diamond X50A over the amateur 70cm band through the 10" SO-239 bulkhead I've installed. . It's pretty typical, nothing to write home about, but note it is covering a 30Mhz bandwidth (huge) and certainly not 5:1 VSWR at the edges!

A 70cm antenna for GMRS is only going to need to cover a little more than 5Mhz and should have very a very low vswr profile.

 

 

 

 

 

[Lscott]

On 10/30/2021 at 2:27 PM, Eltee said:

I am looking for the device that is threaded to connect antenna cable from one side of the wall to the other so I can get my base antenna outside. I don't know what it's called but I thought it looked like a threaded rod that only needed a small hole through the wall. You connected a standard antenna cable on either end, one to the radio and the other to the antenna. Don't know what it is called, where to find it, or if it works well.

Thanks for any info.

Newbie 

What you're referring to is a "bulkhead" connector. It's basically a hard shell version of coax cable with threads on the outside.

I would NOT recommend them for GMRS.

There is a good engineering reason why they should not be used, and likely not on high VHF either. The connectors are NOT designed for 50 ohm impedance to match the coax cable. This results in an impedance "bump" in the transmission line. The longer the bulkhead connector, up to a point, the worse the problem will like become. The problem will appear as an elevated SWR as measured at the radio.

The exact impedance depends on the dimensions of the OD of the inner conductor, the ID of the shell and the dialectic material used. When the impedance is not 50 ohms the bulkhead connector with cause an impedance transformation from one end to the other. The exact transformation is dependent on the impedance of the bulkhead connector and the impedance connected on the end. If these are known the SWR could be calculated. Also being a transmission line the SWR variation will repeat every 1/2 wavelength. The worst are odd multiples of a quarter wavelength. Theoretically a half wavelength should cause no transformation.

When talking about "wavelength" this is the "electrical" wavelength, not the physical length which will always be significantly shorter due to the fact the RF propagates much slower in the bulkhead connector thus the RF "sees" a longer length. You will normally see this accounted for by a specification called the "velocity factor", typically much less than 1.0 which is what it would be in empty space. The same thing happens with coax cable too.

[Eltee]

If I decide to route the coax straight through the interior and out the exterior wall without a bulkhead connector, is there a rule of thumb as to going through vs. over the baseboard? It's a typical painted drywall inside with a flat (no contour) baseboard and the exterior is rough textured stucco. 

 

[BoxCar]

If you won't have an issue with putting a connector on the coax, run it through a piece of PVC pipe. Fill the pipe with insulating foam leaving a drip loop on the exterior portion of the cable just before entering the pipe.

[n4gix]

Alternatively, use a piece of 4" diameter pvc pipe, with a 90º elbow outside. Fill the elbow with steel wool to keep the critters out!

[BoxCar]

15 hours ago, n4gix said:

Alternatively, use a piece of 4" diameter pvc pipe, with a 90º elbow outside. Fill the elbow with steel wool to keep the critters out!

A copper scrub pad won't rust.

[DownEastNC]

22 hours ago, Eltee said:

If I decide to route the coax straight through the interior and out the exterior wall without a bulkhead connector, is there a rule of thumb as to going through vs. over the baseboard? It's a typical painted drywall inside with a flat (no contour) baseboard and the exterior is rough textured stucco. 

 

Ex electrician here. I would cut in a box in the wall at the same height as your electrical outlets and route the cable through the box. When done use a blank outlet plate with a hole in it big enough to accommodate the coax. They do make cover plates with holes in them already if you know what you want. Otherwise do what the cable installers do which is go through the floor as close to the baseboard molding as possible. No offense to cable installers but they tend to do things as quick and as easy as possible so they can get the heck out of there.