[Milsurplus] Was: Strong Stomach Needed. Now ATD questions.

[wf2u at ws19ops.com]

John,

Nice to hear about another potential ATD going on the air.

It's pretty touchy to match the ATD to a nominal 50 ohm system, as the  
output is very low impedance, and the tuning circuit doesn't have much  
range to compensate. You have to connect the antenna with a series  
capacitor. I only had a 100 pf doorknob cap in my junkbox, it's not  
optimum and I didn't get full power (only loaded to about 25 W) and  
plate current. I took a spare antenna tuner (MFJ) and with that,  
playing with the two variable caps and variable coil I manage to get a  
good match between the ATD and the antenna. Output is the specified 40  
W and plate current is also per spec. in the manual.
You could take a variable capacitor (insulated from ground and with an  
insulated knob) and use that in series with the ATD output. There may  
be somewhat less loss using just the one series cap rather than a  
pi-network as in the MFJ.
You can always try to build a replacement coil, but I think you'd be  
better off using a ceramic form for better temperature stability,  
although the unit really doesn't get hot.

Keep us posted on your progress.

73, Meir WF2U
Landrum, SC


Quoting John J Mccarty <jmccarty at alcatel-lucent.com>:

>
> Meir and Dennis;
>
>
> I working on an ATD/ARB combo and had a couple of questions if you   
> have the time.
>
> 1) How are you matching the antenna output to your antenna system?   
> If your using
> coax for the antenna feed line, how does it match up to the ATD. Is an un-un
> needed or will a series cap be enough?
>
> 2) Someone stole the taped inductor (L606) out of one of my 3000-0950 "tuning
> units". Would it be possible to fabricate a new one with a plastic   
> form or are
> the internal temps too high at that point?
>
>
> 73 + tnx
>
>
> John n9hrt
>
> On 7/16/2009 9:39 AM, wf2u at ws19ops.com wrote:
>> Hi Dennis,
>>
>> Nope. Didn't have to replace any resistors.
>>
>> I got the ATD with a few stupid modifications, that I couldn't figure
>> out why they were done. The way I got it, it managed to put out about
>> 4 W on CW.
>> After I removed the modifications and restored the PA circuit to
>> normal (nothing was missing, just some extra components were added by
>> the hacker), it put out the specified 40 W without having anything
>> further to do. Oh, yes, the original Rajah antenna connectors were
>> missing and a UHF type connector was there instead, and a BNC
>> connector for the receiver antenna.
>> I removed those, and Mike Hanz supplied me with replacement Rajah
>> connectors, everything is back to stock. I found a NOS original
>> dynamotor for it, bought the appropriate plugs and made up the cables
>> so the only non-stock items in the setup are the Vinyl jacketed
>> multiconductor cables themselves.
>>
>> The ARB/ATD setup is working great and I'm running it with a 35 A 24
>> VDC surplus Lambda switching power supply. Incidentally, the supply is
>> completely RFI-free.
>> The next thing is to set up the LM-18 after making up the ARB - to -LM
>> cable with the appropriate plugs.
>>
>> 73, Meir WF2U
>> Landrum, SC
>>
>> Quoting mac <w7qho at aol.com>:
>>
>>
>>> Oh come on Meir.  You haven't had to replace ANY of those 18 odd early
>>> composition carbon resistors in your ATD?   About half of the ones in
>>> my set were bad.  If you haven't checked yours would highly recommend
>>> that you do so, especially the series strings of 2-watters in the 814
>>> and 6L6 screen circuits.
>>>
>>> Dennis D.  W7QHO
>>> Glendale, CA
>>>
>>> On Jul 15, 2009, at 9:16 AM, wf2u at ws19ops.com wrote:
>>>
>>>
>>>> I saw that revolting video yesterday.
>>>> This weekend I'll post a video of my original, stock ARB with the
>>>> remote control and tuning dial, running on 24 VDC with the original
>>>> dynamotor, next to a completely stock ATD transmitter as a rebuttal to
>>>> that piece of garbage!
>>>
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>>
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