Dow key relays and Radioworks Line Isolators

[wa2dtw]

1.  Does anyone know how much RF power a Dow key TR relay (with a 110 volt coil) can take?  Will it take the full legal limit on AM?

2.  Does anyone have experience using the Radioworks T4 line isolator?  It is rated at 1500 watts, but with an intermittant duty cycle (CW, SSB, etc).  It is not rated for a continuous duty cycle.  I would like to put about 40 watts of AM through it.  Does that seem reasonable?


Thanks and 73
Steve WA2DTW

[Steve - WB3HUZ]

I've put 300 watts through a T-4 with no problems.

1.  Does anyone know how much RF power a Dow key TR relay (with a 110 volt coil) can take?  Will it take the full legal limit on AM?

2.  Does anyone have experience using the Radioworks T4 line isolator?  It is rated at 1500 watts, but with an intermittant duty cycle (CW, SSB, etc).  It is not rated for a continuous duty cycle.  I would like to put about 40 watts of AM through it.  Does that seem reasonable?


Thanks and 73
Steve WA2DTW

[w5dud]

Hello , I am still using W4KKO,s dow key set up on a 20V-2, not 1 problem, did add a rec delay relay to the set up, Dudley, W5DUD

[k4kyv]

But be careful with sequencing.  When I put my Gates BC1-T on line, the transmitter was still putting out power for a split second after the relay was de-energised, and the guts to the Dow-key turned to a solid block of carbon.  That's why I came up with the relay sequencing circuit that was published in ER.  Now, my antenna changeover relay doesn't have the slightest trace of a spark at the contacts when I go from R to T and vice versa. 

But to be on the safe side, I went to an open frame changeover relay from the 1930's, designed to switch open wire line, with about an inch of spacing between open contacts, and each contact is about the size of a dime.  I purchased it n.o.s. at a hamfest many years ago.  The thing would probably handle 10 kw.  But it malfunctioned after about one month of use.  The manufacturer had used ordinary stranded copper wire to connect the moveable contacts to the relay terminals.  It didn't take long for that  stranded wire to break in two from metal fatigue.  I happen to have a few feet of pure copper wire rope in my junkbox, so I unwound one of the stranded braids and used short pieces of that to replace the stranded wire, and it has been in use for over 3 years now, with no trace of fraying or coming apart.

[Pete, WA2CWA]

1.  Does anyone know how much RF power a Dow key TR relay (with a 110 volt coil) can take?  Will it take the full legal limit on AM?

2.  Does anyone have experience using the Radioworks T4 line isolator?  It is rated at 1500 watts, but with an intermittant duty cycle (CW, SSB, etc).  It is not rated for a continuous duty cycle.  I would like to put about 40 watts of AM through it.  Does that seem reasonable?

Thanks and 73
Steve WA2DTW

Specs say up to 1KW.

[AB2EZ]

Steve

I have a T4 line isolator in my shack. I have been using it for several years. It is in series with the output of whatever rig I am running (E.g. my KW-1 running 400 watts carrier and 1500 watts peak on 160 or 75 meters), and the 50 ohm unbalanced input port my antenna tuner.

It has never given me any problems, and it does not get warm.

However, I don't know how it would behave at 400 watts carrier (old buzzard transmissions) if it were looking into a high SWR.

The only difference between high duty cycle modes and low duty cycle modes (for the same peak power) that one of these line isolators could possibly "care about" is heating. If you don't notice it getting warm, then you should be ok.

Best regards

Stu 

[wa2dtw]

Hi Steve, Mack, Dudley, Don, Pete and Stu
Thank you very much for the info.  I can breathe a bit easier now (without worrying about inhaling smoke or ozone).     
73
Steve WA2DTW   

[k4kyv]

In either case a) or b) care must be taken to insure that the  relay has operated before r.f. voltage is applied to the r.f. contact in the relay.

That's what I found out when I tried to use one with my Gates BC1-T on 160.