View Full Version : President HR2510 10 Meter AM FM Rx problem query

08-28-2012, 01:58 AM
Greetings I wished to post a question if anyone in the past has had the same problem. On the RX on both AM and FM modes there is a steady "blanking" as if the radio is receiving a S3 'dead key', but there is not an incoming signal thus there is no audio output to the speakers.

On the USB, LSB, and CW modes the receive is working fine, and receives very well.
On all modes the TX is working fine also.
I did not know if this a common problem for these radios, so I am asking if anyone else has had this issue before.

I have a general license, but working on radios is not my trade. I can replace parts as needed, *(past soldering experience) but not sure what to even to look for, even with a schematic, nor have any 'real' test equipment, apart from a volt-meter.

I have tested the RX with another radio close by transmitting and was able to determine that the RX on the AM and FM only does not respond properly, and even while transmitting does not "exceed" the S3-4 RX dead key level, but can receive just fine on the SSB modes and CW.
-Thanks for your time.

08-29-2012, 06:23 PM
Try tightening all the screws that hold the circuit boards to the chassis. Also, unplug and then plug in again all of the connectors. That cures a lot of problems in many units including the HR-2510.

I have two HR-2510 units, one is the i.f. for my 432 MHz transverter and the other is used for various things including i.f. for transverters and mobile. From time to time, they get a little "flakey" and tightening the screws and the connectors usually fixes the problems.

Glen, K9STH

08-30-2012, 01:22 AM
I will try that this weekend. Thanks for the suggestion.

08-30-2012, 11:34 AM
It sounds like an AGC fault.
If you look at the schematic HERE


You can see that the radio switches in a different time constant to the AGC in AM/FM using D119.


The design here is poor because the voltage across C41 and C159 (arrowed in red) can change polarity.
So Uniden use a pair of back to back 47uF 10V electrolytic caps C41 and C159. A cheap and nasty design solution on a
particularly nasty model of CB radio. These radios are technically BAD for so many reasons...

If these caps fail and go leaky over time then there will be a positive bias leaked into the AGC circuit via these parts on
AM/FM and you will see the AGC voltage at IC101 pin 14 (arrowed in dark blue) will go UP even with no signal. Normally this voltage will be less than 1V with no signal on all modes. But with this fault you could see several volts at pin 14 on AM/FM and this will make the radio go deaf. You also see an S meter reading even without a signal because the leaked bias also gets into the s meter drive circuit via R39 and this is why you see an S meter reading)

Try removing C41 and C159 and test them for DC leakage. If this is the cause of the fault then my guess is the radio will begin to 'work' if you just remove these two parts but you really should replace them with new parts or a modern equivalent non polarised cap. eg 22uF ceramic.

08-31-2012, 01:12 AM
Parts replacement I can do. Thanks for the info, and will try this also. Parts are common and cheap, I will post if this works after i try it.

08-31-2012, 12:26 PM
OK Bob, hope it helps.

I've seen this kind of fault report now on three of these radios and in every case it was C41 and C159 going leaky and spoiling reception on AM/FM only. I think that once one of them leaks the other follows soon after because the voltage polarity can flip across these caps.

These days you can replace the two 47uF series electrolytic caps with a single (non polarised) 22uF 16V ceramic cap and this fault would be cured for good. If you refit 47uF 10V caps as per the original circuit it could possibly fail again in a few years.


09-03-2012, 07:20 PM
Thanks Jeremy,
I was able to swap those 2 caps out this morning with a day off *(labor day) and the RX came right up. It took some doing in finding the components since not everything is labeled, but after just looking the compoent side over I did see some 10 volt caps, and thought "who would put 10 volt caps in a radio that requires 12-14 volts, input" and the rest is history, lol.
Did not have the exact value of 22uF disc cap to replace but used a 10uF and 15uF in parallel, and figured it would be close enough. The (2) 47uF Caps in series having a 23.5uF capatance -In formula theroy-.

I did see a few more 10volt caps in other locations and figure in time they should be repaced just to avoid a future breakdown.
Thanks again for the quick reference with this problem, and will logg it away for the future. Schematics are useful, but unless you half way drew them its difficult to know what the circuits mean, apart from tracing signal paths.

K9STH Thanks also for the suggestion, also. Since the rig was apart its a good idea to break and make the connections, and even rechecking the screw connections. I fould that to be a problem in some old CBs and handed it back to the driver and just said "You had a screw loose." , and the Driver did not know if I was talking about the radio or him. :cool:


09-04-2012, 04:27 PM
Good to hear it's now fixed :) Yours must be the third or fourth radio I've diagnosed 'online' with this fault.

As you can probably tell from my first post I'm not an admirer of these radios. They do look the part but they are quite grim technically.

09-05-2012, 02:06 AM
LOL. well if I have a President HR 2510 that should should show its age. Once upon a time I was a CBer, and not afraid to admit it, and was able to make a trade for the radio, and figured I would make it a good base station, since it has 5 modes and wide freq range. Last year when 10 Meter was 'open' I was able to make several contacts, with little to no equipt. Its more of a 'classic' rig, not a workhorse.
I do thank you again for the input, and help.

09-05-2012, 07:46 PM
One of my HR-2510 units I obtained through a Uniden vice president. Before being acquired by Vetex, the national headquarters of Uniden America was at the south end of the Dallas / Fort Worth International Airport. I wanted an HR-2600 because of the FM repeater split being available. However, the engineering staff at Uniden actually refused to let the VP get an HR-2600 saying that the receiver in the HR-2510 was considerably better.

Since I was authorizing purchase of up to 100 Uniden commercial two-way units at a time, the VP had no qualms about getting me an HR-2510 at employee price which was less than 40-percent of the retail price.

Frankly, I have had absolutely no problems with the HR-2510 when using it as my 10-meter mobile. In fact, I have over 100-countries worked from my 10-meter mobile using a Larsen NMO-27 (27 MHz to 30 MHz) shortened whip that has basically a negative 3 dB gain. The other HR-2510 that I own is used as the i.f. for my 432 MHz transverter. Again, no problems with the performance.

I wonder if many of the so called problems with the HR-2510 are caused by the expanding of the frequency coverage and, even more so, by the "golden screwdrivers" of people using the HR-2510 either illegally on 47 CFR Part 95 Subpart D ("CB") radio service or by "freebanders" who operate outside of the legal "CB" frequencies. I know that the 2nd HR-2510 that I obtained had been "golden screwdrivered" and had all sorts of problems. As such, I got it for like $10! Fortunately, no components had been damaged but the unit definitely required a serious re-alignment to get it back to where the performance was again satisfactory.

Glen, K9STH

09-06-2012, 09:43 PM
Hi Glen
I think the reason people fall for these radios is because they look so good and have continuous tuning and a frequency
readout etc. They look good so they must be good :)

Note that I'm judging the radio technically both from doing a few basic bench tests using test gear and also from looking at
the circuit design.

It's basically an export CB radio with a ropey synthesiser and a pretty LCD front panel but it has technical issues that make
it worse (to me) than much older CB radios.

So I'm not judging it against regular ham gear. It's such a nasty design I'm slating it compared to CBs made 30 years ago.
eg, bad (as in easy to overload) receiver on FM, poor synthesiser performance, dirty/noisy transmitter, bad MIC amp circuit on Tx, thin audio from the speaker.

These radios look like they were rushed into production with lots of initial design flaws. Uniden have a track record of doing this with their export CB radios.

I do like some of their classic export CBs a lot and can forgive some of the flaws because the overall experience with the radio is a very good one. But this is not the case with the 2510/2830. It's a CB radio that has tried to grow into being a regular looking 10m ham radio but it actually compromises its RF performance in order to achieve the design goal of 26-30MHz coverage and I can't accept the compromise in Rx and Tx and synthesiser performance as being worthwhile.


09-06-2012, 11:17 PM
I have measured the performance of both my HR-2510 units and the performance actually checks out pretty good. Now my original HR-2510 was bought before they became popular for the expanded frequency coverage and definitely came with only 28.0000 MHz to 29.6999 MHz coverage. One unit was made in 1993 in Taiwan and the other was made in 1995 in the Philippines.

Now the receivers are not as good as the more expensive units. However, as checked on my service monitors, etc., the receivers are as good as, and in some cases better than, a number of the lower priced transceivers made by the "big three" that are used by a lot operators around the world. I have no idea as to if those units imported into North America are any different than those imported elsewhere. Another possibility is that, at least for the unit that I got through the Uniden vice president, the HR-2510 may have gotten some "special treatment" to make sure that it worked well.

Glen, K9STH

09-07-2012, 09:40 PM
Just to put my views into perspective, Uniden made lots of SSB CB radios and some of them were quite good. eg some of the 40 channel USA models. But the illegal 120+ channel export radios that flooded the market in the 1980s are full of basic design flaws because the makers came up with cheaper and nastier ways of expanding the CB radios way beyond 40 channels. Themakers like cybernet and Uniden knew the average illegal CB user wouldn't care about design integrity because there was no competitive alternative anyway.

I guess the Lincoln/2510/2830 was the ultimate version of this type of radio in the late 1980s. Behind that pretty front panel is a radio that was rushed into production to grab a slice of the demand for 11m SSB CB radios with a frequency readout and small tuning steps. These model numbers are all CB radios and they are designed to fill a niche area of CB called freebanding. But technically they are poor radios.

In terms of 'expanding' it to cover the 11m band I'm not sure what you mean in terms of how this makes the performance worse. It is first and foremost an export CB radio and all of them are factory designed to cover at least 26-30MHz ( I think they can also go down to the 12m band if you change the firmware) The only mod you have to do to unlock it back to the CB band is change logic levels on the MCU chip. No tweaking required. They also come with the usual CB extras like a roger bleep and a CB/PA button and this is a big clue as to who this radio is really aimed at.

They are locked to the 10m band when new and marketed as 10m radios to get over the fact they are really illegal export CB radios with a pretty LCD display. Most of them get modded straight away to unlock the full 4MHz range because I would think most buyers will be CBers who couldn't give a stuff about how poor the radio is technically. They just want the frequency readout and the continuous tuning coverage and the status of the radio compared to a conventional CB.

The receiver tests I did on it included input IP3 on FM mode, IF rejection, image rejection and resistance to blocking and IF capture. The performance is best described as woeful. It is a CB radio receiver but with the front end selectivity and dynamic range made even worse because they tried to make it cover about a 5MHz span. It is a very sensitive receiver but I'm not sure that it needs to be that sensitive for operation on 28MHz.
On transmit I looked at the (high) transmit noise floor, spurious levels and also the IMD levels from the PA at 21W PEP.

The noise floor of the transmitter is something like -126dBc/Hz and it puts out this noise across a 5MHz slice of the HF band. That's pretty bad for a CB radio. Basically these things will put out a high flat level of noise across the 12m to 10m bands and will interfere with any local users of these bands. Older CB radios don't put out noise like this.

Also the MIC preamp circuit is designed badly. It's based on an older established design but they managed to ruin the performance by adding the modulation detector circuit as this causes distortion terms to be injected back at the mic amp input. Not good!

The synthesiser suffers from annoying spurious terms every 10kHz or so as you tune it across the range. Most people probably never notice this but I can hear them appear and disappear as the main dial is tuned in 100Hz steps even on a quiet frequency. The spurious are easy to spot on test gear.

A typical old school service monitor won't be able to highlight some of the issues. Luckily these days it is quite easy to buy older lab grade RF test gear for very reasonable prices and set up a pretty decent RF workbench :)

09-08-2012, 04:07 AM
I don't have the 10 kHz problem on either radio! Also, don't have problems with noise on the transmitter! Noise on the transmitter would definitely be a problem with the unit that I use as an i.f. for my 432 MHz transverter which goes through a couple of linear amplifier stages with an output of about 175-watts. Around this area there are quite a number of "weak signal" 432 MHz operators including some very serious EME operators including Al Ward, W5LUA, who holds some very serious records on UHF and higher frequencies who lives less than 10-miles from me.

When those HR-2510 units sold in this country are "opened up", the coverage is 26.0 MHz to 29.6999 MHz and not to 30.0 MHz. I have "opened up" both HR-2510 to use with transverters. As such, when used with my 6-meter transverter I can get coverage from 50.0 MHz to 53.6999 MHz, with my 2-meter transverter coverage from 144.0 MHz to 147.6999 MHz, and with the 432 MHz transverter coverage from 430.0 MHz to 433.6999 MHz. Now I don't normally use either HR-2510 units for the i.f. on my 6-meter and 2-meter transverters. For 6-meters I have 2-different single band transceivers and for 2-meters, as well as 222 MHz, I use my Heath SB-301 / SB-401 combination. But, in a "pinch", I can use one of the HR-2510 units as the i.f. for all 3 of those bands.

The Radio Shack HTX-100 was basically the same unit (built by Uniden) except that it has only SSB and CW (no FM or AM). Most people who use the HTX-100 are very pleased with the operation. Again, I haven't heard of any real problems. One thing with the HTX-100 is that Uniden did make it harder to "open up" the unit. Instead of just cutting a jumper and installing a resistor, the crystal standard has to be changed to move it down to 26.0 MHz - 27.6999 MHz.

I really do wonder if the units sold in Europe and the far east are somewhat different!

Now I do admit that I primarily use the HR-2510 units on SSB with a little CW operation. I almost never use them for FM operation (I have a commercial Pace Landmaster II for 10-meter FM operation) and never on AM. So if there are any deficiencies on those modes I would never notice!

For my uses, I find the HR-2510 units quite acceptable. As for operation on 10-meters, the only time I do use the HR-2510 is mobile. For general operation on 10-meters I normally use my Collins 75S-3A receiver, Collins 32S-3 transmitter, and Tempo 2001 linear. I do have a Collins 75S-1 receiver and 32S-1 transmitter and the Eldico R-104 receiver and T-102 transmitter ("S-Line clones") that can be used with the Tempo 2001. Also, have the Heath SB-301 receiver, SB-401 transmitter, and SB-200 linear amplifier that can be used by just selecting the combination on my antenna switching console.

Glen, K9STH

09-08-2012, 10:44 PM
I believe there are different versions of the firmware and some radios do 26-30MHz and some do 26-29.7MHz.

I think all of these radios will have the noise issue because the noise is generated at the low level Tx mixer. The signals going into the mixer measure out OK but the little active Tx mixer chip produces a high noise floor at its output.

I can measure about -126dBc/Hz at the output (pin 9) of the mixer using an RF probe.

Once you look past the BPF that follows the mixer you can see a flat pedestal of noise that is 5MHz wide. This indicates the bandwidth of the BPF.

Put the radio output (via a 30dB attenuator) into a decent spectrum analyser eg an HP8568B and key it up on 10W and you will see the noise.
Then repeat the test on a decent CB radio and you will see a marked improvement in the wideband noise level!

If I get time tomorrow I'll repeat this test myself and post up some plots of the noise and the close in and far out synth spurious. You do need to have a good ear for spectral purity to hear the impact of the close in spurious terms. Most people won't notice this or be bothered.

The other issue with these radios for SSB/CW use is they have a 4.5kHz wide IF filter because of the need to support AM. So this impacts selectivity especially on CW mode.

BTW, I'm not suggesting everyone should stop using these radios on the ham bands. They aren't that bad. I'm just giving my personal opinion why I think they are poor quality radios :)

09-09-2012, 06:06 PM
I dug out an old President Lincoln CB today (same as the 2510) and took a quick Tx plot on an analyser. This radio is the later model with the MRF455 PA and revised PCBs.

This is taken via a 30dB attenuator so +10dBm on the analyser is about 10W. The plot is for an FM carrier just above 28MHz. You can see the big pedestal of noise that gets down to just below 25MHz. It is at about -126dBc/Hz as indicated by the marker

The noise comes from the low level Tx mixer. This mixer is quite weedy and is also a weak link in the Tx chain in terms of distortion levels. Not a good thing but then again this is just a CB radio.

Note that if the test is repeated with a clean +10dBm source into the analyser then the noise level is much lower so the noise pedestal is from the radio not the analyser. I have another one of these radios that arrived here as new and still anti tamper sealed and still on 10m and it is just the same.

I guess it's up to the individual to decide if the above noise level is a problem. If there's no one local on 12m or CB or 10m then I guess it doesn't matter.

I also did some receiver tests to see how easy it was to overload and it was pretty bad. Much MUCH easier to totally jam out compared to a decent CB radio.


09-10-2012, 09:13 PM
What does the noise level look like on SSB?

Glen, K9STH

09-10-2012, 10:56 PM
It should be about the same on a whistle on SSB but I haven't tested it yet. I'll have a look tomorrow :)

To crudely assess the nusiance value of this noise I can do a few quick sums as below.

If a 10W FM carrier is transmitted (+40dBm) and the noise floor power is -126dBc/Hz then the absolute noise power will be 40-126 = -86dBm/Hz.

If we assume a nominal comms channel BW of 2500Hz then the noise power in that channel is -86 + 10*log(2500) = -86 +34 = -51dBm.

So for every 2500Hz slice of spectrum across 25-30MHz it will be transmitting -51dBm of noise power.

This doesn't sound a lot but it could cause an annoying raised noise floor on a quiet band at maybe 1km away if both stations were pretty much line of sight and had decent aerials.

09-10-2012, 11:22 PM
Sorry about the huge size of the last image by the way as it has messed up the page.

Here's a plot of another signal source set to 28MHz and +10dBm on the same analyser settings. You can see the noise is lower. I do have other analysers that have a lower noise floor than this one but luckily this one is OK for this task.

It's my favourite analyser for general RF stuff and it is extremely big and heavy so swapping to another analyser means a lot of trolley wheeling and creaking floorboards :)