Posted: 5/23/2010 8:17:10 PM EDT
|
Hi all,
I picked up an IC 735 on ebay a few days ago and I'm having problems with it. Seems to receive fine, but when I try to transmit the XMIT light comes on but the needle won't fluctuate in response to my voice, it just sits on zero. I tried to respond to several very strong CQs and no one seems to be hearing me so I don't think I'm getting out. Antenna is a dipole that I cut and tweaked for 20 meters and after a bit of trimming the SWR indicates about 1.1. All of this on SSB. When I go to AM the needle is about 1/3 scale up (the carrier I assume) when I transmit and it does "wiggle" very slightly when I speak in to the mic. Anybody have any experience with these radios or just ideas in general? I'm new to all of this amateur radio stuff - getting the VHF mobile up and going was pretty straight forward, but I'm not having the same experience with the HF. Would appreciate any wisdom anybody has. |
|
Could be any number of things. How is your mic gain adjusted? Compressor/processor engaged? Any chance you'd have another compatible microphone available to rule out a malfunctioning mic?
What "needle" are you looking at? Do you have a wattmeter? Or looking at power output or ALC on the rig's meter? |
| The meter "wiggling" as you speak on AM is modulation. It sounds like the mic is ok and there is a problem in the rig itself. Maybe in the SSB audio or balanced modulator inside the rig. Not repairable by mere mortals. Double check your mic gain and compressor settings like mentioned above before sending it in for repair. |
|
Yeah, I picked the unscientific word "wiggling" intentionally to try to draw a picture of the needle not moving much. Just slightly on AM - you really have to look for it. On the other hand in SSB mode it is "dead as a door nail" - sits on zero and doesn't move at all. Corresponded with Scott Malcom of MTS and he suspects a a problem with the mic gain control. I'm going to try a couple of things when I get home and if that doesn't work I'll probably ship it to him for a repair estimate.
Now about this compressor thing. There is a "comp" switch on the unit - assume that's the compressor control. What does it do and where should it be set (on or off) for basic SSB operation? I'm sure these are questions that any idiot ham should know. Maybe in a few weeks I'll have risen to that level of knowledge 
Thanks |
|
Quoted:
Now about this compressor thing. There is a "comp" switch on the unit - assume that's the compressor control. What does it do and where should it be set (on or off) for basic SSB operation? Due to the nature of SSB (and AM) as linear modes, plus the popularity of using all manner of different microphones, HF radios have audio controls for the microphone (transmitter) audio. There is a microphone level control to adjust the "volume", which needs to be set at an appropriate level for good performance and not exceeding the bandwidth of the mode. This adjustment is typically done by using the ALC meter function on the radio to display the transmit audio levels generated by your particular voice and microphone. The "comp" or compressor, is an audio processor (sometimes called "proc" or processor in some rigs) that alters the characteristics of transmitted audio by compressing the audio - it makes the quieter sounds louder and loud sounds quieter. In moderation, this can improve the perceived audio quality as well as improve intelligibility of the voice at the other end of the transmission. To excess, compression/processing can produce distorted, even unintelligible audio and even transmitted interference or spurious emissions. Excessive microphone gain can produce the same undesirable effects. Some radios have fixed compressor/processors, other radios have adjustable ones. Most people experiment with microphones and mic settings, and use meter indications (ALC, and compression if available), headphone monitor (if available), and on-air feedback to make sure they are transmitting good audio. Other amateur operators nearby are helpful for this, to make contact on "dead" HF bands and try things out. In your current situation, if the compressor was on I would definitely turn it off as a test to see if it might possibly be the cause of the lack of audio. If you haven't adjusted or even looked at the mic gain level, it could just be all the way down resulting in no audio - that would be consistent with a very minimal amount of audio. Looking at a photo of that radio, the adjustments are on sliders underneath a panel to the left of the main tuning knob. I don't know if the IC-735 supports headphone monitor of TX audio, I don't see a "monitor" button on there so would tend to think no. If it did, you could connect a pair of headphones and listen to your own audio while TX into a dummy load or something. |
|
Hey, I'm up and running. The tech I talked to nailed it. Said the Mic Gain switch often gets full of dust and to "cycle it vigorously". Did that, problem solved, got my first HF qso with a station 700 miles south of me this evening.
Any ARFCOMM net action on 20 meters? I haven't figured out how to pull off a 40 meter dipole yet - I don't have any trees 60' tall. Thanks for all the input from the folks here. |
|
Quoted:
I haven't figured out how to pull off a 40 meter dipole yet - I don't have any trees 60' tall. Absolutely do not need 60' tall trees for a 40 meter dipole. Even the standard 1/4 wavelength height over ground would only be 33', and an NVIS setup can work just a few feet off the ground especially if you put a reflector under it. In short, just use the height you have and you'll be fine. Glad you worked the problem out. Any potentiometer, especially sliding types like those adjustments on the 735, can get to where they lose proper connectivity between the moving parts, and just running them through the full range of motion several times can often restore proper function. |