[Yaesu] FT-ONE - low output.

[Dr. Gerald N. Johnson]

On 5/28/2011 4:06 AM, David Kirkby wrote:
> On 27 May 2011 23:42, Dr. Gerald N. Johnson<geraldj at weather.net>  wrote:
>> When a rig protects on reflected power, it won't let there be enough
>> drive to get much forward power. If a rig is properly protected it won't
>> be damaged by a high SWR load like an open on the coax connector.
>
> Yes, but that could go wrong, especially since this FT-ONE was bought
> used and I have no idea what (if any) mods have been done on it.
>
>> First check be sure the coax from the rig to the dummy load is good,
>> then that the dummy load is good. Check with an external wattmeter or
>> SWR bridge.
>
> I've measured the DC resistance on the PL-259 plug and it is 52 Ohms,
> so is OK.  The load is a 5 kW oil-cooled Bird one, so I've not blown
> it up! The connection to the Bird had to go via a couple of adapters,
> as I have no cable with N on one end and PL-259 on the other.
> Eventually I'll put an N-connector on the rig - I've done that with
> every rig I've ever owned and every PA I've ever built, though the
> YC-156 amp I started building years ago (but never finished), has a
> 7/16 connector.
>
> I don't have a power meter. I long ago gave up ham radio and only just
> started to get back some interest, so are lacking a lot of basic
> essential items. I have a Bird 43, but no suitable elements. But I'm
> not willing to buy elements for that - see why on the review I put
> yesterday on e-ham

Thing about Bird 43 is that the reading is usually considerably more 
accurate than the typical ham/CB meter.
>
> http://www.eham.net/reviews/detail/374
>
> I'll buy a power meter designed for amateur use in a few days. Bird's
> are so-overrated it is a joke really.
>
> I've bought a 1.3 GHz spectrum analyser from a friend, which I will
> get Sunday, so will have a method by Sunday of measuring power with
> the analyser and a coupler (which I have), but it's not a long-term
> solution. I don't wish to use a spectrum analyser to check a rigs
> output power! A devent meter aimed at the ham market will be OK. I can
> bye one of those for the cost of a single Bird element.

A simple RF voltmeter and maybe resistive attenuator for the coupled 
voltage and work to measure power and reflected power by reversing the 
coupler line connections or if its a dual coupler by moving the RF 
probe, while keeping the coupled port terminated in 50 ohms. That can be 
simpler than using the spectrum analyzer as a volt meter and potentially 
a bit more accurate.

The spectrum analyzer can tell you if the shaft or shaft coupling 
between the mixer stages and the low pass filter has failed leaving the 
low pass filter on 80 meters while your are testing on 20 meters. But 
that should show on the internal SWR meter (often of poorer precision 
than the external SWR meter in my experience) as low power both forward 
and reflected.
>
>> Generally the SWR metering is after the low pass filter that is often a
>> separate module from the PA because SWR metering with the strong
>> harmonics from the unfiltered PA would be relatively useless.
>
> I looked at the service manual last night and it appears the sensing
> is in the ALC unit. I'll check the diodes in that today. If one is
> faulty, I'll get a matched pair of diodes. I guess any Schottky diode
> would do, as long as the two are identical.

Decades ago HP said Schottky diodes from the same batch were matched as 
closely as you could by by selecting them and sold them in pouches from 
the same batch. Compared to germanium diodes the poorest match of 
Schottky are very much better so you shouldn't find much difference 
(probably a little difference in forward drop because of slightly 
different wafer processing) between any pair with the same part number 
and maker.
>
>> Tentecs are known to mess up transmitting because of diodes in the SWR
>> bridge having gone bad. So that's a place to check. A diode not
>> rectifying forward power any more puts the ratio of forward to reverse
>> very high lots of reverse, no forward and puts the rig into shut down.
>> Seems like the Tentec diodes go during thunderstorms.
>
> I hope that's happened here, though if anything it was a high VSWR
> that damaged the diodes, not a thunderstorm.
>
>> 73, Jerry, K0CQ
>
> Thank you Jerry,
>
> Dave, G8WRB.
>
>
>> On 5/27/2011 5:08 PM, Dr. David Kirkby wrote:
>>> I think I've managed to screw up my FT-ONE by transmitting into a bad load. The
>>> collector current is not going above about 1 A. If I used set the meter to FSD
>>> in the forward position, switching to the reflected actually shows beyond full
>>> scale! This is with a 50 Ohm load.
>>>
>>> I'm not sure if the sensing of the RF has gone wrong, so the PA is shutting down
>>> as the reflected power is apparently so high.
>>>
>>> I've not poured over the service manual yet, but does anyone know if the sensing
>>> for forward and reflected power occurs in the PA unit?
>>>
>>> Any ideas?
>>
73, Jerry, K0CQ