.... so I don't release the magic smoke.

I have a Yaesu FL-2100B, LDG AT-100 tuner, Dentron Super Tuner, Icom IC-746, and will be using an OCFD untill I can get the 3 element SteppIR in the air.

What would be the best way to set up the IC-746 to work with the amp?

Unfortunately there is no bypass switch with the Dentron Super Tuner.  You are lacking something in this chain, a SWR/Power Meter.  The Daiwa CNW-801HP is very good.

Hook it up like so:

IC-746  -->  AT-100  -->  FL-2100B  -->  Dentron Super Tuner  -->  SWR/Power meter  -->  Antenna

For a "virtual bypass" with the Super Tuner, set both capacitors to fully meshed, and the band selector on the lowest band (maximum inductance).  Then with the amplifer off (bypassed) you use the AT-100 for tuning.  You can also use the AT-100 for tuning into the amp if one of the band input filters is off a bit.

Some people worry about amps putting a strain on the Tx Send output of Icom radios.  You don' t need an expensive buffer, relay, etc.  You can put these few parts directly on a cable covered with heat shrink, with a phono plug on each end.  Mark the ends "TCVR" and "AMP".



For your amp you want the lower circuit above, the positive voltage circuit.  

The PNP transistor, you can use Radio Shack 276-2027, which is a TIP42G.  Almost any PNP power transistor rated 3 amps or higher will work.

The 1N4002 diode is Radio Shack 276-1102 or 276-1103.

The 1k 1/2w resistor is Radio Shack 271-1118.

Something like this.

RF Path:

IC-746 RF Out (ANT 1) to FL-2100B RF IN to external wattmeter (hope you have one) to Dentron Super Tuner RF IN.  
Dentron Super Tuner Balanced Ouput (ladder line) to OCFD.  You can use coax and a balun instead of ladder line.

Keying Circuit:

IC-746 SEND jack to external keying relay (eBay) to FL-2100B keying line.  The negative voltage on the amp necessitates the use of the relay.
You can also use HSEND off the ACC1 socket (some of the eBay cables use ACC1 for both keying and ALC).

ALC (Optional):

IC-746 ALC jack to FL-2100B ALC connector.

Ground:

Ground all equipment together.

Hope that helps.

73

Edit: Forgot to put the amp in the RF path.

The FL2100B is negative voltage on the keying circuit?  Sorry, I thought it was postive.

In that case, use the upper circuit in my diagram, and for the NPN transistor use Radio Shack 276-2017 (TIP-31) or 276-2020 (TIP-3055).

I have my watt meter (Bird 2500W slug) in between amp and the tuner so I can see what the amp is putting out.  I have occasionally put the meter between the amp and the rig but was wondering why you suggested it.  Not sure if I have mine set up correctly.

You've got it right.  I forgot to put the amp in the RF path in my original post.  Doh.  Thanks for catching it.

You don't need a wattmeter between your rig and amp.  Unless you want to know your drive power in watts (and your rig doesn't give you that info).

Usually the controversy is whether to put the wattmeter before or after the tuner.  I would put it before the tuner.  Most meters are calibrated to 50 ohms impedance.  It should see close to 50 ohms looking into the tuner.  If you placed the wattmeter after the tuner, it would be looking at your antenna's natural impedance.  

Also, I use an LP-100A, which is a combination wattmeter/SWR meter.  Putting it before the tuner allows me to adjust the match for low SWR.  If the LP-100A was after the tuner, it would see my antenna's untuned SWR.  The SWR alarm feature (breaks the PTT circuit in the event of high SWR) also wouldn't work.

Edit: spelling

I had a brain fart.  I wrote:


Gubernator is right, it should be:

IC-746 --> AT-100 --> FL-2100B --> SWR/Power meter --> Dentron Super Tuner -->  Antenna


With your amp off, or in bypass, you can also see what your drive power is coming from the IC-746.  The SWR/Power Meter needs to be before the Super Tuner so you can see what the tuner adjustments are doing.

Thanks for catching that, Gubernator.


As for grounding all components together, do not "daisy chain" them.  That is do not run a ground connection from transceiver to tuner to amp to, etc.

Instead, run the ground connections from all components to one common point.  I have a copper buss behind my rigs with 1" wide braid with a big ring terminal crimped on screwed to the buss.  This braid runs outside to my ground rods.  Then each component is connected with it's own 1/2" wide brain ground strap to that copper buss.  You can also use 10 ga wire for the ground connections to the common buss.

The IC-746 has a built in tuner, is it good enough to avoid issues if hooked direct to the amp, or will the AT-100 tuner be needed to keep the radio safe?
The IC-746's internal tuner has no trouble tuning the OCFD I currently use on everything from 80m up to 6m with the exception of 30m.

I didn't metion SWR/Wattmeters, but I have enough to put one between the radio & amp, amp & tuner, and the tuner & antenna if needed. (Diawa(iirc) cross needle, Bird 43, 2 or 3 AN/URM 120's, & a Dosy 2000.)

SO, not counting meters, the set up should look like this?
IC-746 -> FL-2100B -> Dentron Tuner -> Antenna

If the radio's internal tuner isn't good enough, it would be
IC-746 -> AT-100 Tuner -> FL-2100B -> Dentron Tuner -> Antenna

I need to go back & plot the SWR on the different bands on the OCFD, but I'm thinking the Dentron tuner may not be needed on the bands the amp is designed for. Speaking of which, how much of a mis-match can the FL-2100B safely take? =< 3:1 ?

Once I get the SteppIR up, the tuner can definately go since the antenna will adjust to give a good SWR on 20m & up and I'll use a resonant dipole for each of the lower bands I use.

I need the cicuit above for NEGATIVE VOLTAGE, right?

Not being familiar with the FL2100, you need to check that out somewhere and make sure.  Perhaps find an online manual.

I don't have a tuner between my rig and amp, and I have the internal tuner disabled.  IMO, having two tuners is going to cause you more frustration than it's worth.





 

I couldn't find a reference to the keying voltage in the manual, but did find this info on W8JI's website.

"Early units, the FL2100 and 2100B, used a negative 15-18 volts relay voltage. This line spikes to nearly -100 volts on relay opening."

Of course, if you bought the amp used the prior owner might have installed a keying interface.  I would check the voltage and current on the keying line with a multimeter just to be sure.

Thanks for the info!
Gonna see if I can get it running this weekend.