Well, since 145 is about 1/3rd of 447, let's see how it comes out. 145.46 * 3 = 436.38 MHz. 447.575 - 436.38 = 11.195 MHz
Let me guess; the IF in that receiver is close to, or exactly that frequency! I'm sure the radio uses a much lower frequency crystal and multiplies it up to get to 450 MHz. The last stage is probably a tripler; the ones before it are probably doublers or triplers as well. You might be able to add some shielding around the multiplier stages, if none is there already. Lowering the gain in the stage that's producing the 145 MHz signal might also reduce its output enough to help. Changing to the opposite injection will definitely help, but then you'd need to go through the whole calculation again to find out what other frequency it'll wipe out. Bob M. ====== --- Nate Duehr <[EMAIL PROTECTED]> wrote: > Hi guys, > > Built a link radio out of a MASTR II mobile a while > back. 444.575 TX, > 447.575 RX. > > It is NOT duplexed and the RX section turns off > during TX, just a normal > MASTR II mobile setup. The only modification done > was to by-pass the PA > and run the exciter output over to the Low-Pass > Filter board in the PA > section directly -- didn't need much power to make > this link work with a > 6 or 7 element yagi mounted outside, pointed at the > repeater it's > linking into. > > After having the link installed in my basement for a > few days, I > realized that it's throwing a fairly strong dead > carrier on VHF at > 145.460 or thereabouts, but ONLY when it's sitting > idle in Receive. > When the radio is transmitting the carrier generated > by the receiver > disappears. > > It's not strong enough to receive it further than > about one house away > on an HT down the street, and I don't hear it one > block over, but there > in the house... permanent carrier on 145.46. > (Unfortunately this is the > output frequency of one of our club repeaters that's > over 40 miles and > behind a ridge from my house, and the repeater > "loses" completely to the > carrier coming from the link radio in the basement.) > > I attempted to figure out the mix math to see if > that would be a > "normal" thing to see when using that particular UHF > RX frequency, but > I'm honestly not very good at that. I figured I'd > post and see if any > of the list's gurus might have an explanation of why > it might be doing > this. Any thoughts? > > I might (just to see what happens) stuff the > crystals in another MASTR > II, tune it up, and see if the same thing happens, > but if this could be > explained mathematically, that would be more > "interesting". > > Hmm, what other info might you need... ahh... > thinking back, the > crystals might not have been ordered with high-side > injection... I'd > have to look at the ICM packing sheet, and it's at > home. > > Nate WY0X ____________________________________________________________________________________ Yahoo! Music Unlimited Access over 1 million songs. http://music.yahoo.com/unlimited
