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Reviews For: Oak Hills Research 100A

Category: QRP Radios (5 watts or less)

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Review Summary For : Oak Hills Research 100A
Reviews: 51MSRP: 129.95
Description:
The Oak Hills Research OHR 100A single band CW transceiver kit
Product is in production
More Info: http://www.ohr.com/ohr100a.htm
# last 180 days Avg. Rating last 180 days Total reviews Avg. overall rating
00514.9
KB1NSB Rating: 2007-01-31
Very nice rig! Time Owned: 3 to 6 months.
Had my 100A for four months now, and had over 120 QSOs with it so far , and I'm very pleased with this little rig! Made a few overseas contacts and many coast to coast, and been getting nice signal reports. I did notice a slight bit of reciever drift when warming up, but after 30 seconds or so It's rock stable. I'm using a end fed dipole with it at 27 ft, and getting great results. I plan to get another 100A in 40 meters! Great rig from Oak Hills Research!
N9SKN Rating: 2007-01-11
Proven, stable circuit designs Time Owned: 0 to 3 months.
My thoughts on the OHR100A for 30m.

I selected this kit partially for the proven, and common circuit designs, for the ABX filter, and also knowing it was at least the second version of the model series.

Having a capacitance meter while laying out the caps was a luxury and saved me some worry - as most, but not quite all of the caps are marked as called out in the manual. I know vendors change and these parts are all getting harder to find so no big deal here. Just don't panic if something does not match up - call OHR or measure it.

My kit was only short a single 100pf ceramic disc cap - quickly remedied at Radio Shack. Certainly they would have shipped me one, but was not worth the trouble. I ended up with a couple of extra yellow toroids and a small blue mono cap - so we'll call it even OHR :)

Aligning the kit is what I found the hardest. I used a calibrated S&S freq. counter, a Norcal FCC-1 counter, and a Heathkit signal generator.

For the TX offset setting, the Norcal FCC-1 counter was used to measure the freq. of the VFO (It has good low freq. resolution) and then sample the TX RF output freq. and adjust this for 700Hz less than the VFO. I know this is not the best method, but until I come up with a 'main station rig' it will have to do. Setting the RX LO freq. so as its desired tone is centered through the ABX filter is interesting as well. You can really hear the capability of the ABX filter at work here. I am not done with this adjustment yet.

As mentioned earlier I found it helpful to attach my VOM with RF probe to the audio output to better measure small changes in signal levels while peaking this rig. Poor mans' methods... I know. There is always the option of having the alignment done by OHR.

I had previously read here at Eham that one gentleman (N2KZ) recommended setting the windings on the VFO coil L114 higher than the specified 19.100 Mhz freq. - due to the fact that his freq. only rose back up to 19.097 after his nail polish on the coil dryed. In other words his minimum VFO freq. dropped 3Khz after nail polishing. So considering that helpful advice I set mine to 19.102 Mhz and then sealed it with clear nail polish. When my L114 was dry the freq. was (and is) 19.101 Mhz. So N2KZ shared good advice on the frequency shift regarding sealing the windings. He had a 3 Khz down shift and I had a 1 Khz down shift after sealing. I guess the concern is that the dial index may not line up correctly if the the VFO is not at exactly 19.100 Mhz when using the stock tuning pot.

Personally if I had to do it again I would set L114 right at 19.100 IF planning on using a digital frequency display / and /or optional ten turn tuning pot with the rig, since the freq. should drop 1-3 Khz after sealing. That way you don't loose that 1 Khz at the bottom. Any drop in the freq. would provide the bottom end 'cushion' (The rig covers 80 Khz so it leaves 30 Mhz of cushion on top to play with anyway).

IF I was planning to use the stock 1 turn pot with the nice silk screened face of the provided enclosure for operating reference, then I would consider splitting the difference of these findings - thus setting the freq. at 19.1015 before sealing. This is all splitting hairs, and I know this is a entry level minimum part count rig, but I also agree with N2KZ's review here at Eham that including a trimmer for this adjustment in the circuit really would make it a mute point. On the other hand the kit already has 12 trimmers in it. To me, with the little I know - thats the mark of quality, the tuned circuit promotes signal selectivity as opposed to broadbanded amps, and also a more user defined rig via pot settings for personal preference.

For example, I like the sidetone circuit in this rig much better than my older OHR Spirit II mono-band rig. Its louder and adjustable,(My old one is still very quiet at max.) and in addition also the pitch is adjustable. Like I said before though, 'sampled RF' sidetone may be looked down upon by some HAMS, however I believe its true value lies in a much easier and more accurate setting of the TX offset for those constructing a transceiver without a 'main rig' available, and secondarily, it also provides a relative TX signal strength indication in the absence of TX metering.

I also agree as was wriiten here that the second LM380 audio amp chip provided in the kit's audio chain is a plus - providing some quality speaker volume. If a headphone plug is inserted into the headphone jack, the speaker output is disconnected. The headphones are driven from only the first LM380 stage to not blast ones' ears off, and this also provides finer volume control at the panel pot during headphone operation (A gripe on my other/older single LM380 chipped audio OHR rig). Removing the headphone plug then connects the first stage LM380 to the second stage LM380, and it is those 2 stages combined in series that then drive the speaker jack. It is really different than portrayed in the "OHR100A BLOCK DIAGRAGM" as the speaker uses both stages, but the difference is in a good and smart way IMO.

My rig puts out 4.5W at 12.5 VDC - so I am confident it will do the 5W at 13.8 VDC.

In short - this rig popped right up and came to life with no problems, and it does exactly what OHR said it would.

Some construction pics of this rig at my website: http://home.comcast.net/~banda5
former_AE6CP_LH Rating: 2006-09-10
Solid performer Time Owned: 0 to 3 months.
Just built the 30 meter version and I am very happy with it. Worked perfectly the first time and I get 7 watts output.
The only problem I had were a couple parts didn't match up with the parts inventory. Normal substitutions but there was no mention of them in the documentation. A quick call to OHR resolved this very minor issue.
Thanks OHR!!!
K3MD Rating: 2006-09-02
Works Time Owned: 6 to 12 months.
This was my first kit in around 25 years or so. Sent it in for service, which was very fast and courteous. Receiver works well, have the built-in keyer which works well also. Nice open construction for a QRP rig. The variable receive bandwith is a nice feature.
W2XS Rating: 2006-06-14
Some nice features Time Owned: 0 to 3 months.
I recently bought a 40m model used. The power output was a little low so I replaced the driver transistors. Now I get 7W out at 14VDC. The transistors were inexpensive from Dan's Small Parts. I added a 10-turn pot and tuning is smooth and re-settable. I have had several QSOs all with good reports. The variable bandwidth is a nice feature. I like to keep it wide open when the band isn't crowded. It has an IF amplifier, not often found in these little transceivers, and there are two LM-380 audio chips - one just for the speaker output (which provides very loud audio) and the other for headphones. This extra chip may not be the best for low current draw but I have been using a speaker with good results. There is a nice sound to the receiver, even with no AGC. The case is bigger than I thought, but there is room inside for additions like a keyer, SWL Freq Mite, and maybe a small battery.
K4JSU Rating: 2004-05-11
First Kit Delight Time Owned: 6 to 12 months.
I returned to amateur radio after an absence of 42 years. As a teenager, I built several Heathkits: a DX-20, an SWR bridge, and a VTVM. I homebrewed an FSK modification for my B&W 5100 and used an Army surplus teletype printer. I had an HQ 100 receiver. But college, law school, career and family pushed me away until last year. I looked around - Heathkit is gone! But I settled on an Oak Hills Research kit, the OHR100A 20 meter version, because it looked like a good first kit that I might be able to assemble. And it was. Of course, I could not see the parts with the naked eye (I am 57 years of age and wear glasses), but I bought a round magnifier mounted on articulated arms that bolts to the desk. The magnifying glass is surrounded by a flourescent bulb. I bought from Sears a small padded vise to hold the printed circuit board; the vise attaches to the desk with a suction mechanism. Finally, I got a $20 DVM made in China from Universal Radio (amazing price!) and a 15 watt soldering iron from Radio Shack, and got to work. I had a lot of fun. I could just lose myself in the project, and did. When I finished, I sent it back to OHR to have it aligned, I have enjoyed it ever since. Later I bought an FT 847, but I prefer the OHR100A on 20, mainly because of the full-break in feature. I like the FT 847, but you cannot beat how smooth the OHR100A is on CW. Since then I have built the Oak Hills Research QRP wattmeter, and I am in the midst of building the digital frequency counter. I have gotten prompt and very helpful support via email from Marshall Emms at Oak Hills Research. As a lawyer who charges for his time, I do not know how Marshall can afford to spend so much time with such lids as I am. But he did, and he made me a fan for life.
N2KZ Rating: 2004-03-02
Not your father's Heathkit Time Owned: 0 to 3 months.
This is not your father's Heathkit. The Oak Hills Research OHR-100A is a compact 5-watt single band transceiver sold in kit form. I built the 30-meter version casually in about 16 hours. I would recommend this kit only to those who have an established background in component level maintenance and repair or kit building. The instructions and documentation are comprehensive and fairly easy to understand. It is a thinking man's kit that requires consideration and planning. Read the manual thoroughly in advance! The results are a neat, full-featured QRP transceiver that is well designed and fun to operate.

The most important step may be the first one. It took about an hour to inventory all the parts. This was an essential requirement since several components could easily be mistaken for others in the kit. There was also a confusing slip of paper that asked builders to use a 3 pf cap instead of a 2.2 pf cap. The kit provided only 2.2 pf caps; but a note in the paperwork added clarity. It seems picocaps are hard to obtain and the values supplied were close enough for this design. After you gain a good foundation for building, it's time to populate the board!

Remember the basics: Be as neat as possible and examine all your soldering several times. You will be the one to fix the problems if they occur! Mount all the parts in the same order. Resistor codes should read from left to right. Written values and legends on parts should all face the same direction and be seen. Bend leads with symmetry and care before soldering. Cut the leads before you solder, not after the joint has been made. Cutting first makes a better joint with no fear of micro-cracking the solder. I learned this tip in a MIL spec. soldering school I once attended.

Here are some specific tips for those who will assemble an OHR-100A in the future: The toroids are very easy to wind. Don't tin the leads of the enamel wires before you solder them to the board. The neatest way is place the toroids onto the board, with wires through the correct holes, snip them to size and then scratch away enough of the enamel wire to make a good connection. Pre-tinning the leads looks sloppy! Align crystal Y100 very carefully to allow for room for jack J100 so that both will fit nicely on the board. Press firmly on the Molex connectors P101 - P105 when you mount and solder them. Tack in one post while holding the other two (so you don't burn your hand) and then solder the remaining two posts. Wait until the last minute before inserting the chips into their sockets and soldering the antenna wire to J105. These should be the very last two steps before dropping the PC board into place. Instead of bending out and breaking the tabs from the various pots, bend them in and flush resulting in a nearly sealed pot. When you solder one wire of the cap that attaches to J104, keep in mind where the RCA plug will sit and keep that area clear of solder. The length of the Molex connector wires for P103 should be cut to 5 inches long, not 4 1/2 inches as suggested in the manual. Mount the SO-239 antenna connector so that the legend "SO-239" faces right side up and legible.

Two design items that could be improved: The headphone jack is a mini-jack mono design. Since nearly all headphones are 3-conductor stereo versions these days, an appropriate jack should have been included. Otherwise, you need an external adapter or you'll suffer one-ear-only listening. The "Key" jack is an RCA female. I guess this caters to the external keyer with paddle crowd. Gone are the days of the 1/4 inch phono plugs. I would have liked a mini-phono jack, at least. Both of these items are personal preference.

If you happen to also purchase the memory keyer option, drill the hole for the necessary pushbutton before anything goes into the chassis box. Also clean the paint from inside the "Paddle" hole while you are at it. OHR should add to their design a way to retain the text memories of the memory keyer when you disconnect the power. It may become laborious to reprogram the keyer every time you reassemble your station to a new location.

The most difficult part of the project is the tortuous alignment. Alignment is a two-day process. In day one, you carefully toy with coil L114 until its circuit produces a frequency perfectly on 19.100 MHz. You then seal the coil windings with nail polish to fix them in place. Heed my warning: When the nail polish is first applied, the frequency drops and then begs to return to 19.100 as it dries. It never quite makes it back to 19.100! In my case, it came to final rest at about 19.097. You should try to compensate by sealing your coil while it is slightly higher than 19.100. If your end result does not sit perfectly on that frequency, you will have to compensate by moving the front panel knob into proper position to gain accurate final dial calibration. This procedure is goofy. There should be a small trimmer to make this easier to do. Wait a day for the polish to dry and then move on to the rest of the alignment.

You really need a "main station transceiver" to align this kit properly. Without it, you simply can't continue and achieve viable results. The adjustment of the BFO tone is arbitrary and awkward. I had to tinker with this for quite awhile before I understood what was going on and tweaked it to where I liked it. The adjustments for receiver sensitivity and maximum power output were relatively simple. The setting of the sidetone level and sidetone frequency requires some thought but was relatively painless. You can align this kit by yourself, but it requires thought, patience, a frequency counter, a multimeter and an accurately calibrated transceiver.

My persistence paid off. The rig worked on my first try and I had a nice QSO with a ham in Ohio who gave me a 579. I'm sure I will enjoy and love this rig. This is not a thousand dollar spectacular technology display. It is a simple, concise rig that draws little current and is light as a feather. The feature that drew me to purchase the kit was the variable bandwidth control. It works and works well. The receiver is alive and quite sensitive. The transmitter produces a nice sweet note. The QSK is immediate and seamless.
With only a few reservations, I give the OHR-100A a hearty "bravo!"

- Karl Zuk N2KZ
KY6O Rating: 2003-04-27
Nice rig, great support Time Owned: 0 to 3 months.
I am building up an OHR-100A for a friend of mine, and I wanted to write to tell anyone considering one of these: Try it, you'll like it!

My unit arrived within a week of my order, and they were even kind enough to send me UPS tracking information along with my order.

A quick check of the parts showed that one of the transistors was missing - a quick e-mail, and it arrived 3 days later. I also had two rather unusual minor issues, the main AF pot had cross-threaded itself, so I couldn't tighten the lockwasher, and the final resistor I had to install was supposed to be 47 ohms...All I had left in the bag was 4.7k ohms. Again, a quick e-mail to the OHR support staff, and everything went together fine.

My only caution in building this kit is not to rush it. There are lots of parts, with much board room to install them all. The only "nit picks" I could even mention are:
1. The manual is sparse about testing when something may not be correct. A table of voltages at particular board spots would do wonders here.
2. You really do need a freq counter to align the unit with, otherwise you're better off sending it back to OHR for a factory alignment.

Still, all in all, this one is a joy to build and put together!

KC4FFD Rating: 2003-04-16
Perfect Unit !!! I Love this thing.. Time Owned: 0 to 3 months.
I must give an A+ to the guys at Oak Hills Research. From the time I picked up the unit in person through the finished product I have had a great time. The unit asembled very well with room to spare on the componets. At first power up I heard a CW signal before even tuning. The receiver is as good if not better than any of the big rigs in my shack and the Bandwidth combind with the RF Gain allows me to have little trouble picking out what I want to hear. Make sure you use a well filtered power supply. The power output will hit 6 watts on my unit but I run at 5. If you don't know your diodes, Ask before getting started building your kit as they can be hard to decern from the manual. The support team at OHR can help with all your questions. The PCB is well labled and it's just a good looking unit. One more quick note is to read the section near the back of the manual on substitution of parts before starting. It may save you some time!!
About one week of spare time and you can be up and running!!
AA1BW Rating: 2003-01-23
Good radio Time Owned: more than 12 months.
I have the 20M version, using it for a year now. It was easy to put together, gave me good fun. It took me about 10 hours to slowly, put it togther.
It was alive as soon as DC was apllied. Alignment is easy, and the receiver is hot. The only thing I don't like is the too much noise. Its receiver is a noisy type, but picks up all signals well.
The TX is good, solid 4 Watts out.
QSK is just great, could not be better.
Front panel, and controls are excellent. One can see that the designer really operates the HF bands, and knows what controls are essential.
The variable bandwidth, RF gain, AF gain, RIT, Freq is adjustable on the front panel.
I have the 10 turn pot and keyer oprions installed, the make it a perfect radio. Mine tune from 14000.25 Khz to 14082 Khz. So anywhere I set the dial, I am within limits.
Anyway I built the optional Freq meter, but dont use it always. I dont need to know my exact freq to communicate succesfully within the band.
A fun radio, good price, it is a little bit larger than ususal, but this makes the front panel easily accessible, and the PCB is also easier to put together.
Have fun with it
Lajos (HA0DR, AA1BW)