The AM Forum

I've started using 75 ohm coax and nice, compression F connectors on my receive antennas.  What a pleasure it is to put one of those on with the correct tool instead of soldering on a PL-259.   They are waterproof and cheap.  DX Engineering actually recommends this now for receive antennas so I don't feel like a hammy hambone when I do it.

But can you transmit using them?  I assume not but why not?

The only thing I'd worry about is the spacing for voltage insulation. If you are real picky, the tought of a 75 Ohm connector might bother you but at HF it is likely not an issue. I'd bet it would do 100W levels without trouble.

My Heathkit HW-101 and HW-16 both had RCA connectors for an antenna jack. Needless to say, I changed them to SO-239's.

100 watts max is the most I'd ever try.

I will admit to running 100 watts through about 200 feet of RG-6, with F connectors on both ends, to a 10 meter vertical antenna mounted up in a tree. I used "F" to "PL-259" adapters at both ends. It worked fine for years on 10 meter FM and never gave me a bit of trouble. In fact, the same length of RG-6, which is out in the woods and buried under about 6 inches of soil, is currently used to feed one of my receive loops. As others have indicated, I don't think I would trust a setup like that at anything higher than 100 watts, and on AM, I might de-rate things a bit more.

I have to agree about the simplicity of installing F connectors. They crank on easily, and crimp perfectly every time. On top of that, RG-6 is very cheap and very low loss at HF-VHF. I use that stuff for all my receive-only HF antennas and scanner antennas.

if you want decent 75 ohm coax you can get heliax with that impedance and 75 ohm andrew N connectors.  MaxGain sells N to F adapters (someone does, I think it is MaxGain but don't hold me to that).  I hate to be the one to say it but if DX Engineering sells something, that's more likely to make it hammy hambone  :D  These are the guys who sell little radial kits,  a bunch of wires cut to some length with lugs crimped on them so Hammy doesn't have to do any lug crimping himself.  They go with the radial plate.  Full disclosure:  I have and use one of those radial plates so I am something of a self-identified hammy hambone myself  ???

But anyway, if you are worried about power and AM duty, 75 ohm heliax and the Andrew 75 ohm N connectors will handle it.


Rob

I have seen the better connctors the cable and Sat people use and they are much better for waterproofing. They have a little more meat to them. Spacing might still be a problem for higher power.

Fred

Some of the ones the Sat guys use actually have gel inside them as well to seal against water.  Looks like petroleum jelly.

F connectors CAN get somewhat pricey, if you get the GOOD ones.

I do NOT think they are constant impedance, though... Like the PL259, they ain't 75 ohms......  It seems I read that somewhere years ago, talking about using them in stations.

--Shane

I just found a site by VK1OD about using RG-6/U for transmitting.  He doesn't recommend F connectors but he does make a case for using RG-6/U for transmitting.

I noticed this sentence:

The breakdown voltage of RG−6/U is typically around 2.7kV, which would be reached at a power level of nearly 50kW in a matched 75Ω system.

Heck I don't run that even on my good days.

http://vk1od.net/transmissionline/RG6/index.htm

R,

" Full disclosure:  I have and use one of those radial plates so I am something of a self-identified hammy hambone myself  ??? "

The first step to recovery is to admit that one has a problem. We are here to help.


klc

pl259 isn't 50 ohms

Roger, Roger 4-10 good buddy.
PL259 not 50 ohms
Type-N is

Fred

Neither is my antenna  ???  ???  ;D  ;D

I agree.  It's not 75, either.

My point was, the F connector, LIKE THE RCA and PL connector are not 'constant impedance' devices.

After breakfast, and rereading it, I can see how it was taken to mean unlike the PL.


--Shane

I have been using a technique for decades that W6SAI recommended.  Works perfectly and I have cables that are still in good condition after 20+ years.  It involves a BIG iron, a tubing cutter and DON'T use foam RG-8 style cable.  Those interested, I'd be happy to share the info.

That aside, I ran across what I think is an excellent web page on connectorizing cables with PL-259s.

http://www.bcdxc.org/pl259_crimp_on_connectors.htm

I'm going to look into this method mostly because it offers some sort of wx proofing.  I do NOT  recommending using F connectors - but that's just my $0.02 worth. 

I like doing my own BNC (non-crimp) connectors for RF power applications under 100 watts, "N" connectors for UHF applications (again, non-crimp).  Once learned, connectorizing with BNC and N connectors is not difficult.  I still have BNC cables that I made 30+ years ago.  It's worth the effort to learn how to put these connectors on correctly.  I have accidentally removed equipment still connected with my BNC cables and caught the equipment with the sheer strength of the cable to connector connection from hitting the floor.

Al

Ive run 1200W CW/SSB on 80/75 thru RG-6 using F to UHF adaptors at both ends for about 15 years with no problems. This is a sloper off the 100' tower and is used as an angle filler for the high inverted V when chasing DX. Ive run up to around 150W carrier on AM to it also.

Carl

People would be amazed at what a connector will take.

I've shoved 10 grand through a BNC at 10 meters before...  Same thing as an N connector...  But it sure doesn't LOOK like it would take that!

--Shane

The original OP was aware of impedance, but was concerned for the skimpy design and running legal limit through it.
I was surprised that Carl pushed 1500 watts through one. Musta been a flat line.
Fred

Just 1200W Fred ;D

VSWR got up to 2.5:1 at 3900. It is actually parallel elements cut for the CW and SSB DX segments where the VSWR was quite low. With such a low RF voltage and low duty cycle modes it survives well.  I wouldnt want to try the 250TH's on 3885 8)

Carl