Drake AM reception

Discussion in '"Boat Anchor" & Classic Equipment' started by KD5TXX, Apr 23, 2012.

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  1. KD5TXX

    KD5TXX Ham Member QRZ Page

    First off I know it is not an ideal AM rig.... I have a TR4C that works great on SSB. When I turn it to AM It seems like it loses its ears. I was trying to hear a couple of QSOs today and the sound was real bassy. I know of no way to adjust this. Sounds fine on SSB. Is that just AM or is there something I can do?
  2. K9STH

    K9STH Ham Member QRZ Page

    You need an i.f. filter that is considerably wider than the 2.1 kHz SSB filter that is standard in the unit to receive AM. The better equipment from that era (Collins S-Line, Heath SB-Line, Drake 4-series, etc.) have i.f. filters with excellent "skirts" that work very well for SSB. Unfortunately, for AM they are way to narrow to get any decent audio response. Filters with a bandwidth around 6 kHz work very well and give good audio response.

    Glen, K9STH
  3. WB2WIK

    WB2WIK Premium Subscriber QRZ Page

    As Glen said, you really need an AM filter. The SSB filter is way too narrow to produce any sort of fidelity that's understandable.

    One thing that kinda-sorta works is tuning your receiver intentionally off-frequency, which will make the signal somewhat weaker but boost the high frequencies so they're a bit easier to understand. Not a great solution.
  4. KA4DPO

    KA4DPO Ham Member QRZ Page

    Unfortunatlely there is no AM filter for the TR4C, at least Inrad doesn't make one. That rig uses seperate filters for Upper and Lower sideband and in AM mode it goes to LSB. The filter bandwidth is 2500 HZ so it will not sound too good. Like Steve said, you can tune to the low side of the filter to get more high frequency but it was never really intended as an AM rig. I had the same problem with my TR4CW and the only AM I ever listened to on it was WWV.
  5. WB2WIK

    WB2WIK Premium Subscriber QRZ Page

    Actually, although I never did this with a TR-4(C), you can probably bypass the filter altogether (with a jumper rather than a filter) and make it sound very good on AM. I have a TR-7 and that's a very common "work around" in lieu of an AM filter: You just use jumpers on the board where another filter would go, and now you have about 8 kHz bandwidth which sounds quite good. I'd have to research the TR-4(C) schematic to see how plausible that really is, but I'll bet it's been done.

    Might contact WB4HFN or another Drake expert to find out.
  6. KA4DPO

    KA4DPO Ham Member QRZ Page

    You might be able to do that but I have a feeling the mixer images would be a killer. The TR4/TR4C and CW were single conversion 9MHZ IF. It would be interesting to see what it would sound like if you did bypass the filter. Even though they will transmit poor quality AM I don't think they were really intended for AM operation. My T4XB will transmit AM but it is not very clean. The R4B on the other hand is great AM receiver and is far more pleasant to listen to than my Jap radios.
  7. N2EY

    N2EY Ham Member QRZ Page

    What does "loses its ears" mean?

    You need to understand the difference between the modes.

    A typical AM signal consists of lower sideband, carrier, and upper sideband. About 6 kHz wide for good voice communications.

    A typical SSB signal consists of just one sideband - the carrier and other sideband are removed. A bit over 2 kHz wide. The TR-4C is designed for SSB.

    So what you need to do is to tune in AM signals so that the receiver allows one sideband. What you are probably doing is just tuning for maximum S-meter reading, which gives you part of both sidebands and the carrier, but not a complete voice signal.

    Try this: When you find an AM signal, put the rig in SSB mode and listen. You'll hear the carrier heterodyning with the BFO. As you tune the rig, you'll hear the carrier tone get higher and lower. Tune so the carrier tone goes lower and lower, until it disappears. Then switch to AM mode.

    73 de Jim, N2EY
  8. W8ZNX

    W8ZNX Subscriber QRZ Page

    Ahoy Curling Fans

    few bits

    in AM mode TR-3 / TR-4 line of xceivers receive AM poorly

    receives AM best in SSB/exalted carrier

    for the TR-4 CW there is a mod to replace CW filter with a wider AM filter

    I do not want to give up the CW filter

    use receiver that works better on AM

    hook it to the TR-4


  9. W4OP

    W4OP Ham Member QRZ Page

    I modified my TR-4CW/RIT by adding an INRAD 6KHz filter. I machined a bracket and the filter fit right behind the CW filter (from memory). I then replaced the RIT control with one that had a push/pull on/off switch. Reed relays mounted on a custom PCB that also held the filter, switched the relay in when you selected AM. ALso, when that switch was pulled out, it illuminated both the LSB and USB lamps to indicate that both sidebands were now being passed. I think I have a full set of photos if anyone is interested.

    Dale W4OP

  10. KO6WB

    KO6WB Premium Subscriber QRZ Page

    There is another possiblity. There is a 6Khz AM filter for a 9Mhz IF. It should work with no modifications except of course putting it in place of another filter.
    It's at; http://www.inrad.net/product.php?productid=116&cat=147&page=1.
    I see from Dale's posting that he uses exactly this same filter.
    Hope this helps
    Last edited: Apr 29, 2012
  11. KA4DPO

    KA4DPO Ham Member QRZ Page

    There is one problem with that. There are only two filters in the TR4C, there is no CW filter and no provision for one so in order to use the 6KHZ AM filter he would have to give up USB or LSB, or find a way to switch them without causing any blow by.
  12. KO6WB

    KO6WB Premium Subscriber QRZ Page

    Yes I did mention that one of the filters would have to be removed. The one that makes the most sense would be the LSB filter. This is the filter selected when the TR4C is receiving AM. That would make sideband operation on 160, 75 and 40 impossible. However it does not preclude the operation of DSBSC which is allowed. As well as conventional AM operation. Granted, operating like that may not make you a lot of friends, it still means you can operate. Unless there are nearby stations then it is doubtful any SSB operator would notice the extra sideband if they have already tuned you in on LSB.
    The installation of the filter and still having the use of the original filters would require some doing. The addition of more shielding and a switching technic that is better than what a relay would offer. Some have had good results with diode switching. You would have to select the diode for this purpose very carefully.
  13. W4OP

    W4OP Ham Member QRZ Page

    Perhaps I should have been more clear on my posting of adding the AM filter to my TR-4CW/RIT. No filter was removed. The INRAD AM filter was selected when the mode switch was in the AM position. Separate reed relays for input and output enabled this relay. As I was able to fit this PCB into the CW/RIT model, it should be even easier on the non CW model.

    Dale W4OP

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