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  #41  
Old 03-02-2014, 12:41 PM
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Harder to find D3023 and D3039.
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  #42  
Old 03-02-2014, 12:47 PM
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If I had to guess it would be D3021 on 2m or D3019 on 70cm that are suspect.
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  #43  
Old 03-03-2014, 08:39 AM
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How in the world do you get this stuff so fast, wow??? Are you an EE?

I haven't had chance to open it up yet. I emailed the guy from the yahoo group back and got this. By the way it seems like you two are on the same page.

"Look on page 55 Service Manual bottom Right Hand corner. If you follow circuit trace from Q3024 (2SC3102) collector lead towards the right, notice the trace leads to input of LPF----VU TX RF trace. Follow to R3069 33ohm 1 watt resistor which leads off to right from VU TX RF trace. Throght L3031
to D3019 and D3022 which lead off right to end of Schematic These are the two PIN diodes I mentioned , D3019 is the one I found bad in the rig I worked on. It is SMD components and not for the faint hearted soldering tech.
Should be 5vdc on tX at anode and about 0.2 to 0.5vdc drop at cathode or just do the usual check from circuit trace solder pad to anode, circuit trace solder pad to cathode, then anode to cathode, and the reverse ie; cathode to anode for ohmic checks. NOTE*****SMD capacitors at each end woould block DC continuity, but couples RF through, therefore in circuit checks okay.
Most DVMs have a diode check function selection or just measure the resistance thru. Should be close to infinite reverse biased. Will be low ohms resistance forward.

Also note from my previous email to you. The section that I'm pointing out is the UHF transmit path. If, the diodes not bad-----something in that section indicated most likely your problem as that is confined to 440Mhz. There is a separate section above it for two meters or VHF. At the end of that chain trace is the sensor for your SWR/FWD metering-----any variance in SWR readings would have to be outboard of that sensor-----hint hint.
D3054
"

One more note of interest. I had a similar problem on this radio when I was trying to TX on 70cm using a 2m home brew copper J-pole. The radio wold occasionally work on 70cm as I originally described the problem. However, at times when it would not TX on 70cm it would not TX on 2m. I did not use the radio in this manner too often for fear of damaging something. When I switched to an Arrow dual band j-pole the TX was flawless but I have not used it more than one time so far. Seems I am in the phase of more building/configuring things than talking these days.

I am not sure where this leaves me other than Yaesu tech facility as I do not posses the SMD tools nor skills. I very much appreciate the time you have taken with this.

In reply to my j-pole update here is what he said: "sometimes it's as simple as a resonant length of coax at 144 or 440 Mhz. and RF getting back into the transmitter on the 857. Bad ground, especially with a vertical antenna can be instigator. If, you have an external meter or a antenna analyzer, by process of elimination one could discover if it's RF getting back into circuits or if a component is bad. Even water getting in the coax from a leak at the PL 259 connectors outdoors can cause crazy intermittent.

I wish you the best of luck with your situation. Here I use a two step process: What is working-what is not working. What "can" cause it to exhibit these symptoms.
"

A leaky coax at the j-pole could have been at least part of the cause for that issue as that antenna had been up for a few years even though I did water proof it pretty well.

Unfortunately I am not near as versed in these type of diagnosis as you two are and then there is the matter of the SMD skills to fix it!!
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  #44  
Old 03-03-2014, 08:56 AM
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Yup, B.S. in electrical and electronics engineering in 2002 from CU-Denver, emphasis in RF, microelectronics and power. I took a couple of graduate classes in EM/RF, but never really got anywhere towards the M.S.E.E. Also hold my professional engineer's registration in Colorado. Up until about a year ago I worked designing control & data handling and solid state recorder modules for spacecraft. Not a lot on the uplink and downlink stuff, so the EM/RF side I really last did big time in engineering school and the radio hobby is to keep somewhat familiar with it. Well, other than EMI/EMC and signal integrity on PCB designs and the dynamics of SMPS.

I can solder SMC at home. So even though I don't currently have access to a really nice qualified lab, I can deal with anything in my radios. I never got good enough to even try taking the NASA qualification tests, so I obviously could not do flight hardware, but I fixed and modified breadboards and engineering models all the time and the engineers at SEAKR sometimes would build our own module test jigs, especially at the conceptual stage. Don't mistake, though, I am /not/ good at soldering. These 0603 and 0804 sized stuff and ICs with HUGE tabs in radios is cake compared to 0402 discretes and BGAs in really dense designs, though.
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  #45  
Old 03-03-2014, 09:59 AM
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BTW, based on your SWR readings I somewhat doubt it's a resonant length of coax causing your issues. A short or high impedance causing an issue is possible on the J-pole issue, hard to say there. But measuring SWR in this case is a solid way to know what your load is doing. IOW, it doesn't matter if an antenna is effective or not at radiating RF but if SWR is low then you can reasonably conclude you are not getting RF reflected, at least none at the measurement point (e.g. it's possible for load reflected energy to be absorbed by the feedline in theory, although you'd see issue like melted insulation or RF interference).
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  #46  
Old 03-06-2014, 09:11 PM
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Ha, I knew it. Good for you to have the educational background compatible with one's hobby. Must be nice to be able to get into a radio like that and fix it. I will keep those pics handy should I decide to pursue. So I guess you have a FT857 as well?

I have been out of town so I will do a bit more antenna testing in the next few days. By the way, on the FT857 group I read this below that was at the end of an unrelated question to the one I posted. Seems like this type of radio response may be associated with what I am experiencing.

"Also I was too anxious to concern myself with it's technical performance when I first got it and discovered a weird issue with 70cm that really is no problem at all, but it caused me to think mine was limited to about 6 or 7 watts on 70cm. On 70cm the radio is quite sensitive to reflected power and apparently reactance near the VHF/UHF connector. I have one particular VHF/UHF SWR/Power meter that works fine connected with a 2 or 3 foot patch cable on other radios, but when connected to the FT-857D causes the power to fold back even if the SWR is low. With that same meter connected on the end of a 10 foot patch cable everything is fine. It quickly folds back power from 22 watts to 10 watts anytime the SWR reaches 3:1. It does not fold back power so much on 2 meters at 3:1. On 2 meters it folds back from 50 watts to 40 watts and then more as the SWR increases. So if you get low power out on 70cm, don't be concerned. "
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  #47  
Old 03-15-2014, 10:36 AM
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So I thought I would wrap this up. Using my Kenwood TM D710, some more testing shows the flexi whip to work very well on 2m and okay on 70cm. On 70 cm I can hit the nearby low azimuth repeater full quieting. The Pikes Peak 70 cm repeater report was 40% white noise but readable (inside my garage on 5 watts), recall no line of sight to the Pike Peak repeater. For my 70cm mobile needs I think this will be just fine as it is my low overhang/tight trail antenna. Looks like I got lucky on trimming the antenna Normally I run the 5/8 wave Larsen in the roof mount.

Now for my FT857. I took it back inside and hooked it up to the Arrow dual band J-pole. The SWR went up to 2.5 and no TX on 70cm. On VHF it was fine. So there is definitely something wrong with the circuit as described above. I was referred to affordable radio repair in Floraence, CO (http://www.affordableradiorepair.com) by Dave at Centennial electronics here in the Springs.

Thanks again for all the help Dave. By the way, you may be interested in our NM expo trip, we plan on stopping by the VLA
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  #48  
Old 03-20-2014, 08:13 PM
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So I didn't really close this out with what I did for an auxiliary mount. Here are a few pics. It bolts against the tabs for the RTT mounts. Its hard to tell but the antenna sits halfway between the sunroof and windshield.

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  #49  
Old 03-20-2014, 08:34 PM
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That's cool, I like that solution a lot. You could add a couple of radials pointed forward. Bet that would improve the performance.
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  #50  
Old 03-24-2014, 02:21 PM
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Took a few sweeps of the STI-CO antennas I have. These are not lab quality, done in the driveway with a hasty calibration and a couple of adapters. Each grid line represents a change in VSWR ratio of 0.5 and the reference lines are 1:1 (e.g. zero reflection measured at the S11 port) and 3:1.

The one cut correctly for 2m shown across the 70cm band. Looks awesome at 430MHz and pretty good generally. Sweep goes from 420 to 480MHz, center is 450MHz and each step is 25MHz. The prominent dip is ~435MHz at almost 1:1 SWR. Through the bulk of the phone part of 70cm the SWR flirts with 2:1.
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Here's a correctly cut (per formula) 1/4 wave across the same sweep. It doesn't look all that great to be honest, most of the band sits around 2:1 SWR. Main dip is ~443MHz at 1.05:1 SWR (I calculated 445MHz as my intended center). I think the noise is not due to the antenna but the feedline and connectors. Also seems there is some sort of a strong local interference that I can't find, which is partially why my plots have a sine wave imposed on top of them.
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The same antenna in my full configuration, patch cable to duplexer broken out to two antennas cut for each band. Difference in this one to the previous is the cable and MFJ duplexer, which clearly have influence. I suspect the length of patch cable at 9" probably is the main reason, but both seem to show a lot of effect of the connectors, coax, etc. Very ugly plots. Also shows my antenna is still not trimmed short enough on 70cm, but before I go cutting more off I want to figure out the duplexer dependency.
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Same as last one just swept across 2m. No surprise, very little to see, narrow frequency range, wide bandwidth and VHF. Range is 140 to 152MHz, center is 146MHz and the SWR is 1.05:1 at 146.50MHz.
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A 50 ohm resistor at the VNA output for reference. This is a crappy test load, a PL259 with a RF resistor soldered inside of it. This shows how bad the PL259/SO239 interface is at UHF. The resistor is useful out to 1GHz and is 51 ohms, e.g. should show almost a perfect 1:1 SWR (within reason) but at 70cm the connector impedance is anything but uniform. Can't blame much of this on my skills since it does show correctly at lower frequencies (you can see the SWR rising coming in from the left and continuing across the sweep).
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