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Author Topic: OHR-100A build review  (Read 330 times)

AC9QC

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OHR-100A build review
« on: February 07, 2022, 04:10:04 PM »

Okay, I don't have a ton of pics those went away with one of my last phones nuking its self. This kit was generously given to me by a member of eham along with a BitX40 that's still in the wings to complete. You know who you are, feel free to speak up if so inclined. I started this build in less than optimal circumstances using a butane powered soldering iron as the rest of my gear was in storage and wound coils. I would classify it as a moderate build difficulty and I probably have probably about 16 hours all in. It's all through hole, there's just a lot of parts and a moderate board density. The instructions can be somewhat less than clear at moments too in my opinion. I still have as of yet to complete the alignment to my satisfaction as I still seem to be down some power but I want a better method to make that determination first. The kit says it should draw 7-800mA on transmit, based on my PSU's meter I'm not even close. Maybe I'll try another meter or a different alignment technique to check my power. I've been told ATU100s aren't exactly super accurate in the power department at QRP levels without firmware hacks otherwise I'd get mine out and go for it that way.

I probably spent 2-3 hours winding coils, about another 10 hours soldering and installing parts, then another 1-2 hours in the final assembly. I will say that I was amused that I was picking out CW stations on this with full quieting in my basement. While it was connected to the signal generator.

In terms of the alignment I'm not exactly 100% foreign to it but I'd still qualify my self at best a hair above a newbie. I do not like their capacitors, If I can find a drop in sub that uses a different screwdriver to tune I will gladly swap these out. Also, I consider the method of setting the base oscillator frequency (you basically mess with the spacing around a torrid coil) to be somewhat concerning as I'm not sure how that would do with microphonics and if I'd trust it as a field unit due to that. I'd much rather have something a bit more fixed with an adjustable capacitor quite frankly. Will it matter over time? Honestly no clue at all if it will be. It's just my observation.
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N8NK

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Re: OHR-100A build review
« Reply #1 on: February 08, 2022, 02:31:37 AM »

Hi there...
In my experience with homebrew transceivers, some of which are similar to the OHR-100, the approach taken for local oscillator alignment is not only typical- but probably the best in terms of microphonics and drift.
In my work with low drift LOs (VFOs), to have a ceramic trimmer cap in the oscillator determine frequency or set the alignment is to welcome drift with temp changes and normal warmup. This isn't to say that I don't use them- as I really feel that initial drift is not an issue at all unless you're in the habit of having hour-long ragchews with it or for digital use.
Next worst is a TOCO style variable inductor in the LO circuit to set operating frequency. Same problem as with ceramic trimmer caps- opposite drift direction.
If your turns are loose, once it's aligned, glue them in place with glue. 'Model airplane' cement is ideal; it's 'Q dope'. Polystyrene cement. You can make your own out of styrofoam... but I digress   :)
The worst offender in a toroidal inductor based oscillator are long leads on the toroid. Keep 'em short to reduce induced microphonics.
Your power output will come up- as you align it and the current draw will come into line unless there's something wrong in the unit.
Good luck...
Chuck
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AC9QC

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Re: OHR-100A build review
« Reply #2 on: February 11, 2022, 01:25:43 PM »

That's interesting, I haven't glued it yet I figured I'd wait first and see how the alignment worked out.  I'll have to get some airplane cement as I have this one and the BitX40 to play with too. That one has a PIC based VFO with it though.

I'm guessing no one takes the conflicting coefficients and tries to use them to compensate one another?

I try to keep the leads short as it keeps the inductor tight to the PCB. I don't like stuff like that flopping around.

I hooked my oscope up to the 50 ohm dummy load I have and was getting a bit over 20VPP which comes out to about 4W RMS based on my calculation. I think it's not 100% tuned in but it's not terribly off either. I also realized that I didn't have a ground from the connector to the PCB so I added one. I don't recall it in the instructions which seems odd to me, and it infers that the case should be the ground unless I missed the additional wire which is certainly plausible.
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