HF newbie questions

[POD]

g'day all, as mentioned in the thread in General Chat, there's obviously a lot of knowledge of HF in the community here, so here's the first of my silly newbie questions;
Radio is a Codan 8525 with remote head, Jenal SC-2 microphone, moonraker auto-tune antenna with Codan controller.
When I make a voice call, the Tx light in the radio does not seem to glow at all. I have done a beacon call with the SC-2 and the tx lamp glowed very brightly, also glows when tuning the antenna so the LED itself is clearly intact. Is the brightness (or lack thereof) of the tx light any indication of transmitting power? Could not make myself heard any further away than about 100km in sked the other night.

[rover-56]

The brightness of the tx led is directly proportional to tx power in a Codan. The radio is clearly transmitting, so it looks like there may be a problem inside the mic, maybe ptt switch, loose connection, or faulty microphone element.
Carbon elements can lose effectiveness if they are old, or have been exposed to moisture. They are easy to replace.

Since you were able to be heard nearby, I would suspect the mic element.

Cheers,
Terry

[POD]

The Jenal SC-2 mic was given to me by DeanoH (thanks Dean!) and wired into the radio by me with guidance from Alan of Jenal communications (can't speak highly enough of how helpful he was, fantastic product support for something he probably sold years ago), the tx light behaves the same way with 2 standard Codan microphones as well, but all 3 mics are probably pretty old.
What exactly is the element, would it be a generic component? Just a matter of a couple of screws and a couple of wires to fit a new one?

[rover-56]

Could be an electret type which is a small cylinder about 1 to 2 cm dia x 1cm long, or a carbon insert type which is much bigger, more like 4 or 5 cm diameter, fairly obvious when you get the handpiece open. Both are generic 2 wire or solder connections, not polarity sensitive.
You just need to get a replacement which physically fits. Jaycar and Oatley and probably RS Components usually stock them.

Terry

[POD]

Will open the mics up tomorrow and make visit to Jaycar, time permitting, they have a branch near my work. Last time I went in there a couple of weeks ago, the bloke who served me was the 8th dwarf, Surly. I'll look for someone else this time!

[rover-56]

Will open the mics up tomorrow and make visit to Jaycar, time permitting, they have a branch near my work. Last time I went in there a couple of weeks ago, the bloke who served me was the 8th dwarf, Surly. I'll look for someone else this time!

Another possibility I just thought of is that Codans have a microphone amplifier inside the main box. If the radio is misbehaving with several microphones it could be that the amp isn't working. It is possible to still be heard faintly without the amplifier, but not have enough microphone power to give full radio output on voice tx.

Bit more complicated to fix but worth keeping in mind.
Lara Electronics are good with Codans.
30 McIntyres Rd, Lara VIC 3212, 0407531588

Terry

[Kevin B]

Could be a much simpler fix than that, first need to know where/how its installed, is it in vehicle or are you bench testing, HF modulation is very susceptible to stray RF where as a CW tone which is generated to tune your antenna is not so much.

[Kevin B]

Could not make myself heard any further away than about 100km in sked the other night.

That is not uncommon in HF operation and could be conditions, there have been many an instance were I have been working a HF band and could not be heard between 500km and 2000km away yet have no prlem being heard 10000km away in the same same sked, 10 mins later it changes, thats HF propogation for ya.

[DeanoH]

Hi POD, from memory (although it was a few years ago) the Jenal mike has a built in (set once) 'volume control' so that it's output level can be correctly set to suit different HF sets. I think this was also mentioned on the Jenal web site, but as I said it was a few years ago.

Hope it woks out OK. :)

Deano :)

[Kevin B]

microphone Drive Level

Newer versions of the SC2 and SC3 (PCB Version 3 on) have an adjustable in-built microphone pre-amp. This pre-amp is also fed with a fixed level of selcall signal so that setting the voice level output power to a suitable position should result in an adequate selcall output power level.

Have a look here
Intersting microphone.

http://www.jenal.com/page102.ht

[POD]

microphone Drive Level

Newer versions of the SC2 and SC3 (PCB Version 3 on) have an adjustable in-built microphone pre-amp. This pre-amp is also fed with a fixed level of selcall signal so that setting the voice level output power to a suitable position should result in an adequate selcall output power level.

Have a look here
Intersting microphone.

http://www.jenal.com/page102.ht

This mic has software version 2, looking at the programming manual there doesn't seem to be any adjustment for voice level, only for selcall output level. Beyond that, all the instructions about testing output level etc are a bit over my head and involve equipment that I don't have.

[Kevin B]

Has this Microphone been used previously on you radio?, the programming instructions a little hazy in explanation, however looking at the Schematic it indicates to me that VR1(Variable Resister 1) does adjust the Audio level not just the Selcall level, and by bridging LK2 (Link 2) removing Resister 17 from the circuit it would give about 70% extra gain on the microphone as the instructions say it does, looks like they have written it arse about though to me as both Selcall and audio are on the same pin adjusting 1 would directly effect the other.

Sorry if that sound technical...

Buy a new mic :wasntme:

[DeanoH]

Kevin, the mike was previously connected to an old RFK 101 ? HF set which worked OK into VKS 737 Adelaide (from Gippsland) when last used about 9 months ago.

Deano :)

[Kevin B]

Your first point of checking should be to find an "original known working" mic and plug it in to test, find someone in your area that has one and plug it in and give it a go.

Just looking at the Mic specs and it says mic needs

6 to 13.8 Vdc nominal, 55 mA maximum, approx 8mA idle
(30 mA with backlight LEDs)

Now this could be a problem too if pin 1 on your radio does not supply power or enough of it, it does not mean it would not work just the mic insert will not operate powered as it should, this could cause low audio on transmit and low RF power as well, a previous poster said that "The brightness of the tx led is directly proportional to tx power " that is technically half correct the other half is "the TX power level is directly proporional to the modulation" meaning the louder you talk the more TX power is generated, thats why you get a solid light when you tune up, the radio is sending a TONE so it is a contant signal to tune to (those with codans test this by whistling into your mic while keying up, you will see your transmit light go solid, mimicing a CW tone), i wont get into the Specifics of how SSB works but suffice to say if you mic insert is not getting enough power then you wont generate enought modulation and in turn enough TX power.

check the voltage on pin 1 of your codan and see if it falls with in the Mic's required specs.

[POD]

Your first point of checking should be to find an "original known working" mic and plug it in to test, find someone in your area that has one and plug it in and give it a go.

Just looking at the Mic specs and it says mic needs

6 to 13.8 Vdc nominal, 55 mA maximum, approx 8mA idle
(30 mA with backlight LEDs)

Now this could be a problem too if pin 1 on your radio does not supply power or enough of it, it does not mean it would not work just the mic insert will not operate powered as it should, this could cause low audio on transmit and low RF power as well, a previous poster said that "The brightness of the tx led is directly proportional to tx power " that is technically half correct the other half is "the TX power level is directly proporional to the modulation" meaning the louder you talk the more TX power is generated, thats why you get a solid light when you tune up, the radio is sending a TONE so it is a contant signal to tune to (those with codans test this by whistling into your mic while keying up, you will see your transmit light go solid, mimicing a CW tone), i wont get into the Specifics of how SSB works but suffice to say if you mic insert is not getting enough power then you wont generate enought modulation and in turn enough TX power.

check the voltage on pin 1 of your codan and see if it falls with in the Mic's required specs.

This is something I did whilst fitting the Jenal mic to the radio, I had to make new connections at the mic socket in the remote head, including taking a wire from the 12v power input inside the remote head and connecting it to the mic socket to supply 12v to the mic. I'm very confident there is 12v there.
Part of the process of fitting the jenal mic meant that I can no longer plug a standard Codan mic into the radio other than the 2 mics that I have which have been slightly modified to suit. The standard arrangement has the internal speaker connected via 2 unused pins on the mic socket, the mic plug has a bridge from pin 5 to pin 7 so that the speaker only works with the mic connected, this is apparently so that a base station headset can be used. As there are not enough pins left to run the jenal with this arrangement, I bypassed this connection internally, and accordingly broke the bridge between pins 5&7 on the two Codan mics that I have. Hope that all makes sense, the upshot is that I can't try a 'known good' standard mic on my radio, only option would be to try my mics on another codan set, would have to track one down.

[Kevin B]

This is something I did whilst fitting the Jenal mic to the radio, I had to make new connections at the mic socket in the remote head, including taking a wire from the 12v power input inside the remote head and connecting it to the mic socket to supply 12v to the mic. I'm very confident there is 12v there.
Part of the process of fitting the jenal mic meant that I can no longer plug a standard Codan mic into the radio other than the 2 mics that I have which have been slightly modified to suit. The standard arrangement has the internal speaker connected via 2 unused pins on the mic socket, the mic plug has a bridge from pin 5 to pin 7 so that the speaker only works with the mic connected, this is apparently so that a base station headset can be used. As there are not enough pins left to run the jenal with this arrangement, I bypassed this connection internally, and accordingly broke the bridge between pins 5&7 on the two Codan mics that I have. Hope that all makes sense, the upshot is that I can't try a 'known good' standard mic on my radio, only option would be to try my mics on another codan set, would have to track one down.

Yes makes perfect sense POD, mate this is gonna sound silly but its not meant to be, but have you checked and rechecked your solder joints, even the best techy gets caught out by a dry one every now and again, yes your mic on another radio would be the best option, if you could find one around

[POD]

Your first point of checking should be to find an "original known working" mic and plug it in to test, find someone in your area that has one and plug it in and give it a go.

Just looking at the Mic specs and it says mic needs

6 to 13.8 Vdc nominal, 55 mA maximum, approx 8mA idle
(30 mA with backlight LEDs)

Now this could be a problem too if pin 1 on your radio does not supply power or enough of it, it does not mean it would not work just the mic insert will not operate powered as it should, this could cause low audio on transmit and low RF power as well, a previous poster said that "The brightness of the tx led is directly proportional to tx power " that is technically half correct the other half is "the TX power level is directly proporional to the modulation" meaning the louder you talk the more TX power is generated, thats why you get a solid light when you tune up, the radio is sending a TONE so it is a contant signal to tune to (those with codans test this by whistling into your mic while keying up, you will see your transmit light go solid, mimicing a CW tone), i wont get into the Specifics of how SSB works but suffice to say if you mic insert is not getting enough power then you wont generate enought modulation and in turn enough TX power.


check the voltage on pin 1 of your codan and see if it falls with in the Mic's required specs.

Probably displaying my ignorance, but does this mean that there is no 'carrier' signal? This is a term I remember from a mate who was into CB radio back before it was even legal, as I understood it the radio was transmitting an unmodulated signal any time the mic PTT was activated. If I understand the above, would that imply that the Tx lamp will fluctuate with voice volume? Might the low signal strength problem be just that i'm not speaking directly enough into the mic? Just trying to get my head around what is all pretty new to me, I'm someone who likes to fiddle and problem solve my own stuff but electronics is still a dark art for me. Appreciating all the advice, don't know what we did before the interweb!

PS will also check those solder joints, won't get a chance before Monday though.

[superquag]

Yes, you're correct. There is no 'carrier' when you key the xmit without speaking. Therefore no output - and no modulation LED. Put simply, SSB only produces AND amplifies / transmits the information-carrying RF energy. This makes it eight times more efficient than AM, where the carrier is always produced/transmitted, but conveys no info.

This means that you can't check SWR whilst on SSB mode by keying the mic, it needs a tone or set it back to AM mode.

[POD]

I have finally had a chance to get back to this wireless today, I checked all the connections that I have made to ensure no dry solder joints, all seems okay. I called in on the skeds this evening and found that I was not being received at all with the Jenal mike, but getting out okay with a standard Codan mike. Did a couple of beacon calls before sked time and the Jenal mike is selcalling with plenty of power but the Tx lamp does not even illuminate when I voice call with it.

I've had a good look at the internals of the Jenal and I can't figure out how one bridges the appropriate link- more accurately, I can't figure out where the points on the PCB are to link to make LK2 in order to increase mike output. Can anyone point me to a way to interpret the schematic into the actual layout of the PCB?

[POD]

I've made some progress with this thing since last posting, largely thanks to an exchange of emails with Alan of Jenal Communications. As I was getting strong selcall output with the Jenal microphone but no voice output, and getting strong voice output with the standard codan microphone, Alan outlined a diagnostic test to determine whether this was due to a dead mic element or, as he put it, I might have one of the 'very few' 8525's that were set up for data transmission. well just my luck, I have one of the Very Few, thus a small modification to the radio is necessary to enable voice transmission with the Jenal SC-2. The test involved shorting the PTT output direct to earth whilst depressing the PTT and making a voice transmission; in this manner I was able to make contact (albeit faintly) with Meekatharra base the other night from my place near Drouin, which I found pretty encouraging.
Alan has sent me a schematic of the microphone preamp circuit in the radio, along with instruction to bridge across the terminals of C22 on the preamp board, which will apparently then enable voice transmission with the SC-2 microphone.
Two problems with this; I don't know which is the microphone preamp board in the radio, and I don't know how to locate C22 on the board! Is this something that someone may be able to help me identify? I'm sure I can make the appropriate solder connections, but determining what is what inside the radio is outside of my skill set. Would be great if there's someone out there who can point me in the right direction.

[rover-56]

Hope this helps.
This is a part scan of a later 8525/8528 Circuit, yours should be similar.

Follow the wires from the mic socket and they should lead you to the mic amp part of the board.

C22 is on the input to the 1st transistor, it will be labelled on the circuit board.

Good luck:)

Terry

[POD]

Hmmm....this must be how someone who can't read feels every day.
I've identified which board is the microphone amp but only a very few of the components are labeled on the board. There appear to me to be 3 capacitors linked to the transistor, all different types. Think I'd better take it to someone who knows about this stuff or I'll let all the smoke out.

[POD]

I took the remote head of the radio to a friend-of-a-friend who runs an electronics design and manufacturing outfit near me, he identified the appropriate capacitor and bridged the terminals as instructed. Tonight I got a chance to call in during sked time and get a radio check from VKS-737 Alice Springs base, the radio is working a treat:) Going to renew the element in the microphone just to be sure it is optimal.

[rover-56]

Excellent! Glad you got it sorted:)

Terry