If it's the same as the FT-900, and very likely it is, then you can check for the CW narrow filter by pressing the CW mode button that toggles the filter in and out. You will hear a clear difference when the filter kicks in. The SSB filter is more difficult to identify because once installed it is always active and my own experience is that I could not hear the difference between the delivered ceramic and the Collins or Yaesu SSB filters.

73
Robin
OZ6ABM

Even better, try to improve the antenna - it pays in the longer term (for all radios)

73

There is absolutely no power out in CW or any other modes. I suspected that the gain pot may be damaged/cracked, but that's not the case.

Robin

Hi -

All modes, all bands, no Tx out. It's not the PA because I have tried it on another FT-747 and it worked fine. The The Local Unit, FM board and Filter boards are also fine - all these worked when placed in another FT-747.

So its the Main board that's the problem. I checked the power out on the Tx out connector (that goes from the Main board to the PA) and there is zero coming out of it. Have checked the Mic Gain and Drive pots on the front unit and they are OK.

Any clues?

thanks and 73
Robin

My bet is that one of the coax leads between the top and bottom halves of the radio have come undone. If I remember correctly there is a caox lead from the RF unit to the local unit, and that feeds the low power through to the PA stage. Check that lead to make sure it is seated properly. It's not a big issue splitting the radio so it opens like a book and accessing these leads.

73
Robin

I have a FT-747GX that has some strange Tx behavior. Sometimes when I press the PTT on the microphone (USB/LSB), the needle on the meter moves from 0 to 3 mark and stays there without even speaking into the microphone.

If I use CW, FM, AM then I get the needle fluctating wildly anywhere between the 3 and 9 mark.

I have checke the Drive pot and all those inside the rig, all are clean. Strange is that this can happen sometimes, stop for a few hours and then restart.
If I use CW and turn the audio up I can hear a sort of "whooping" sound as the needle fluctuates...?

Any suggestions?

thanks
Robin

Hi Owen,

A few clarifications...

- All measurements were made with an AIM4170 analyzer.

- Yes I was referring to the resistance and reactance components, which in the AIM4170 are indicated by Rs (containing Xs and Cs) and Rp (containing Xp and Cp) where Cs and Cp switch to Ls and Lp as Theta changes.

- Measurememts have been made to calibrate the feeder line and thereby null its effect (approx. 30m of Aircell 7) so the analysis is as if made at the antenna connection point.

- I did actually see your artcles before, but what still confuses me is the exact relationship between reactance and resonance. As I understand, resonance is where the two components cancel each other though not implying zero impedance as a result. However best SWR (theoretically 1:1) is achieved where Z is 50 Ohms or closest therero. The frequency where Z is 50 is not necesarilly the resonant frequency, the resonant frequency can be lower or higher in frequency thaan that where SWR is minumum, and here Z can be significantly lower or higher than 50 Ohms.

So if my measurements are based on the attachment point at the antenna, that is no feedline affect need be taken into account, should I optimize the antenna so the frequency of desired operation is resonant but still ensuring an acceptable SWR?

Am I still confused?

Thanks and 73
Robin

Hi,

Can someone pls. clarify some things as regards antenna theory. I have reads lots of opinions about this, but have no clear answer...

An SWR plot from 0 to 30 MHz of an antenna clearly shows where SWR is lowest. For example, SWR is 1:1.096 at 14.280 MHz.

The same plot also displays the total magnitude of the impedance - calculated from the parallel and serial components. Using a 50 Ohm feeder cable, the Z at 14.280 MHz is 53.024 - the parallel and series impedances nearly cancel each other here. However, at 14.198 MHz the Z is 50.358, which is even better than 53.024, but here the SWR is higher, 1:1.173.

Question 1:
===========
If the antenna is best resonant at 14.198, why is the SWR higher than that at a "less resonant" frequency? In my way of thinking the impedance matching closest to the characteristic of 50 Ohm should give lowest reflection and best SWR.

Question 2:
===========
On the same plot I also find other frequencies where the SWR is good, for example in the 18 m band, but here the resonant frequency is not lower but higher than that of the best SWR for that part of the spectrum. Is this a problem?

Question 3:
===========
If I am using feeder cable with a characteristic impedance of 50 Ohm, should I always be aiming at antenna design with total impedance magnitude of 50 Ohm? For example, I have a dipole where best SWR on 80 m is at a frequency where the Z is approximately 35 Ohms (SWR 1:2.175), but at Z=50 the SWR climbs rapidly to 1:2.650 because it is a very narrow bandwidth antenna. At 3.5 MHz the SWR is 1:2.4 but the Z is much lower at 31 Ohm. What is best here - 31 Ohm, 50 Ohm or ...?

Thanks and 73
Robin

Thanks for the info Charles.

Yes, from what I have heard it does need the capacitance hat, but interesting is the OK SWR on 160 and 80, after that it gets bad.

It also seems that built in ATs in HF rigs can't tune more than a 5:1 mismatch, that I discovered on an FT-950, though it may differ on other models.

thanks again
Robin

Hi,

Today I spent many hours trying to tune a DX-A sloper. I am getting matches of 1:2  on 160 and 80, but on 40 it is a different story. The best SWR I get on 40 is 1:5, and when I look  at a scan using my Array Solution AIM 4170 I see it gets no better than 1:5 at 7.1 MHz. If it did get down to 1:2 in 40m then I would at least know that the length of the sloper must be adjusted, but it just never gets below 1:5.

The setup I have is not optimal. The two slopers are about 120 degrees apart, and the entire setup is hung over a tree branch at about 40 feet using a nylon cord. The slopers are free, but of course there is no yagi above for a capactance hat. Grounding has been added by using a thick braided copper wire that runs from the mounting plate down wards along with the coaxial feeder.

I had to remove quite a length on the 80m sloper and also on 160m to get it to reach the desired SSB frequencies that I use, but at least I could see the SWR was always ay 1:2 somewhere for these bands and it was just a length adjustment issue. The 40m band won't tune anywhere, from 5.1 MHz and up the SWR is 1:5 or worse.

Is there something that would specifically affect the 40 band from getting a low SWR? It seems strange that the SWR curve just about flattens after 5.1 MHz. I do have vegetation in the area, but then again it seems OK for 80 and 160. If I swing the slopers then the frequency of lowest SWR does move maybe 100 KHz, but it does not decrease the SWR for 40m.

Hope you can give me some clues.

73
Robin
5P5R

Hi Alan,

You are correct, but I did modify the amp with the soft key options and I am using it with an IC-718 and FT-900 without any problem.

Thing is on both the above radios the connectors are standard RCA and stand-alone for TX GROUND, while on the FT-747 it is a pin or two in an 8-pin connector and the description in the manual seems to be contradictory.

73
Robin

Hello,

I am trying to connect an old Yaesu FT-747 to a Heathkit SB-200 amp.

The FT-747 has an ALC phono connector, but what confuses is the connection to the ANT RELAY on the SB-200.

In the FT-747 operating manual it says the Band Data connector must be used (page . Must I connect to pin 2 (TX GND) and what else? Then on page 12 it says that the pin 6 is used to control t/r switching of the linear amp?

Can someone explain and clarify?

thanks and 73
Robin
OZ6ABM

FT-900 is a great rig, but depends on the price. If you can get one in good cndx. with the AT and CW and SSB filters installed for about 500 US$ then that should be a good buy. I have a few of these rigs and the build quality exceeds that of the modern FT-450, but of course there are aging problems and there is no fancy DSP and stuff like that.

Robin
5P5R

I haven't owned an FT-450, but have considered buying one myself. I recently saw one working and I must say that I was not impressed. While it has a lot of functionality it seemed cheaply built and tacky. I have other Yaesu equipment, and maybe this is a sign of the times, but I strongly believe that a unit like an FT-900 is much more solid, even if it doesn't have DSP. On the other hand, at the price they are asking for an FT-450 it's probably an OK buy.

73
Robin

I have a 718 and the Noise Blanker works very well. On 10m it doesn't cut all the noise, but reduces from S7/8 to S1. On the other bands I hear no spiking. This is static spikes from an electric fence pulsing once per second and that's abt. 100 feet from the base of my antenna.

Robin
OZ6ABM /5P5R