[Yaesu] FT-ONE - low output.

[David Kirkby]

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

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.

> 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.

> 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?
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