FT-7 SSB TX power level

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Clive G7LUC
Posts: 4
Joined: Wed Feb 19, 2020 5:46 pm

FT-7 SSB TX power level

Unread post by Clive G7LUC »

Hi folks,

For those who did see my previous (first ever) forum post, I'm a total HF “newbie” even though I've held my old “Class B” licence since 1992. I'm recently retired and just setting up my first HF transmitting station centred around a 1979 vintage Yaesu FT-7 transistor portable.

The FT-7 is a really good unmodified original example with a super-sensitive receiver for which the model is renowned. Nominal output for this model on transmit is 10W CW and SSB. I have had two UK QSO's so far , both SSB on 80m, so the TX is certainly functional. The problem is that power seems to be down.

Using a power meter of known accuracy and using dummy load, CW power is a healthy 12W, no problem. But I can't get more than 5W on SSB, even shouting into the mike at point blank range. I've tested the mike (the original Yaesu fist type) on an audio amp and its as good as any other dynamic mike in my collection in terms of sensitivity and volume.

Adjusting the mike level on the FT-7 seems make little difference. It's calibrated 1-8 and anything above 2 gets the same 5W maximum output on the power meter. The lower scale on the S meter is for the PA transistor collector current on transmit. This shows 3 amps on CW but only about half that on normal speech levers for SSB, never above 2 amps.

SSB is new to me except for what I had to learn about it to pass the RAE in 1992. But it seems to me that the transmitter is not getting enough drive on SSB. Or, if you like, the modulation level is too low. This is assuming that 10W is actually supposed to be achievable on SSB on this set?

I have the Yaesu manual for the FT-7 which is pretty detailed but a can't seem to find anything about “modulation level setting.” I know about the “two tone test” but don't have a 'scope so that's out, I'm afraid.

Does it seem to you experienced folks that my FT-7 is down on SSB transmit power?

Your advice always very welcome.

Clive
VK5TM
Posts: 242
Joined: Sun Oct 28, 2018 11:40 pm
Location: South Australia
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Re: FT-7 SSB TX power level

Unread post by VK5TM »

My FT-7 peaks around 15 w with a decent whistle into the mic on SSB (in to a dummy load).

Most common problems can be fixed by individually removing and reseating each plug in card.
Clive G7LUC
Posts: 4
Joined: Wed Feb 19, 2020 5:46 pm

Re: FT-7 SSB TX power level

Unread post by Clive G7LUC »

Thanks for that, Terry and good to meet another FT-7 fan - maybe we can have a G to VK QSO one day just using our Fox Tango Sevens! I had all the boards out when I got the set as it had been unused for some time. I bought it from another Terry, Terry Stowe G0SWS (unless you emigrated and are the same!) who sold it on behalf of his Royal Naval Amateur Radio Society branch. They had just used it for field days, apparently.

I'm new to SSB, only ever used FM gear previously (together with a couple of ex-pmr PYE AM sets.) But I did more research and found a really good Youtube video on getting accurate SSB power readings from Conor M0GVZ. He demonstrated various techniques including the whistle method. But he showed that the only totally accurate method was to use a power meter with a PEP reading and what he referred to as a PEP "hold" function (but possibly "average" is the same on different makes of meter.) I don't usually splash out on new gear but I went ahead and bought a meter with this function, an Avair AV-201, about sixty quid with the postage. I haven't tried it yet but that should settle the matter. And with up to 1kW power capability, it's a good investment anyway.

I can also now see why speech compression and similar audio processing techniques are incorporated into new rigs - I could never see the purpose before. So I've learnt a lot which is what the hobby is all about.

Thanks again and 73's

Clive
VK5TM
Posts: 242
Joined: Sun Oct 28, 2018 11:40 pm
Location: South Australia
Contact:

Re: FT-7 SSB TX power level

Unread post by VK5TM »

Clive G7LUC wrote: Thu Feb 27, 2020 4:15 pm Thanks for that, Terry and good to meet another FT-7 fan - maybe we can have a G to VK QSO one day just using our Fox Tango Sevens! I had all the boards out when I got the set as it had been unused for some time. I bought it from another Terry, Terry Stowe G0SWS (unless you emigrated and are the same!) .......

Clive
Not unless he emigrated in 1965 :lol:

It can always look like you are getting low power out when using anything mechanical (ie moving coil meters) to measure ssb power, the inertia of the needle slows it down so much it can't actually show the peaks, which is why some meters have the peak hold circuitry built in.

I've actually got 2 FT7's and an FL110 100w linear amp.

One FT7 and the amp are in full working condition, the other is in the (very slow :D ) process of having a new RF motherboard and digital VFO fitted.
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