My FT1000MP left my shack about a year ago and is now in service with another local amateur. One of the issues that I had with it when I owned it was the purity of the transverter output. As I was asked about the issue again the other day, here is what I found.
I used the FT1000MP on 14MHz to drive my JavornikII 2m transverter, however the comments here apply equally if you are transverting from 28MHz.
The transverter output has some rather undesireable spurii either side of the main carrier. The offset from the main carrier varies as the VFO is tuned across the band so they cannot be filtered out. At worst they are only 45dB down on the main carrier. If you are running 400W into a decent antenna system these spurii are going to cause problems for other local stations.
Reducing the drive level cleans up the output and the spurii dissapear into the noise. This may not be an option in all cases as the transverter output level is already very low.
The best option for me was to run the rig at about 25W into a power attenuator. This provided a cleaner signal at a level sufficiently high to drive my transverter. I am sure the IMD performance was worse though.
A long time after I moved over to a K3 I received a mail form a well known UK amateur who had spent some time looking into the problem. Unfortunately I don’t have his permission to post his email here but he pointed me at this article by Tom W8JI. If you have ever carried out a factory reset on your FT-1000MP the chances are that the IF TX gains are all set to default.
The FT847 is a great little radio but (in my opinion) has one major flaw. VOX is always on. If the radio is left in CW mode and you touch the key, it will transmit.
If you are running the rig in a system with a mast head preamp or a high power amplifier this can cause problems, and in many cases may cause damage.
The solution adopted by many FT847 owners is to pass both the microphone PTT and the key signals through an external relay. This is not entirely foolproof as the front panel MOX switch is still active. However, there is another, more elegant solution.
On the tuner interface socket there is a signal marked TX INH. Pulling this signal high prevents the radio from generating any RF. Keying the microphone, pushing the MOX, or touching the key will still put the radio into TX but no RF will be produced. Usefully the PTT lines from the STANDBY socket still work which make interfacing to an external sequencer even easier.
Below is the circuit that I use to allow the FT847 to be sequenced. It all fits neatly into the 8 pin connector shell.
U1 is a 78L05 5V regulator. R1 is shown as 1K but can almost vertainly be higher, 10K will probably be fine. D1 is a schottky diode. The type is not critical, I used a BAS16 that I had to hand.
An alternative to this circuit would be to add a pull up resistor to the TX-INH line inside the radio but of course that means opening the radio.
Thanks to PA4EME for suggesting using the TX INH signal.
This works on my FT847, and at least two others that I know of. It may not work on yours. I accept no responsibility whatsoever for any consequences of using the method described above.
My 2m station is in a good location on the North Downs in Kent. It is also line of sight to several broadcast transmitter masts which present a few problems for my receivers. Mast head preamps are a non starter for 2m.
Almost every receiver that I have ever owned has suffered from strong signal problems from the band 2 transmitter at Wrotham. If I connect a microwave power meter to the 2m array (2x17ele) I can measure several mW of power from the anttanna when it’s pointing at Wrotham. Most of the RF is out of band, predominately between 88 and108MHz.
Here is a screen shot with the antenna connected to the anaylser. The antennae are pointing directly at Wrotham. To the right of centre is GB3VHF on 144.43MHz, slightly left of centre is a pager signal probably from the same mast at Fairseat. GB3VHF peaks at around -40dBm if I beam that way.
Below is a closer look at band 2.
For the past 8 years or so I have used a simple notch filter to deal with this. However, it’s performance isn’t that great and lets through more than I’d like.
This is the response of the notch filter. The blue trace is insertion loss, green trace is return loss. Peak attenuation is -31dB at ~93MHz. Insertion loss is around 0.5dB
Years ago I purchased a helical filter manufactured by Aerial Facilities Ltd. It’s beutifully made and has a much better response than the notch filter. It was originally on ~137MHz. I am still trying to tune out the lump slightly HF of the bandpass and improve the insertion loss.